—_. = —_ — — —— ~ ll HI llllllfllyfllllllflllfllw Willi!" THESiS 3 LIBRA R Y I ' Michigan Sac: This is to certify that the thesis entitled 'IHEEFFECI‘OFCOLDEXPOSUREON'I‘HE SODILMANDWATERBALANCEOF'IIE PORCUPII‘IE,EREI‘I-HZONIX)RSATUIVI presented by Stephen Paul Rogers has been accepted towards fulfillment of the requirements for M. S . degree in ZOO-logy /% /4J642/ Major professm Date %”MW 079/ /7/1 7 U I 0-7639 OVERDUE FINES; 25¢ per day per item RETURNING LIBRARY MATYPFALS: Place in book return to remrve charge from CerUI“‘”u :ec-rn< Lam ‘-\\\\ t ‘ Q4r~lfr ‘3‘."l/I 1 24¢ _-—-.—- .«fi—‘H—w‘ '1‘- THE EFFECT OF GOLD EXPOSURE ON THE SODIUM AND WATER.BALANCE OF THE PORCUPINE, ERETHIZON DORSATUM By Stephen Paul Rogers A.THESIS Submitted to IMichigan State University in partial fulfillment of the requirements for the degree of MASTER.OF SCIENCE Department of Zoology 1981 ABSTRACT THE EFFECT OF COLD EXPOSURE ON THE SODIUM AND WATER BALANCE OF THE PORCUPINE, EREI'HIZON IIDRSATUM By Stephen Paul Rogers The impact of winter on the sodium and water balance in the porcupine was evaluated by the collection of animals prior to winter (November) and in late winter (March), and subsequent analysis of various body parameters. Serum sodium concentration in juveniles and pregnant females were seen to decrease by late winter, although adult males maintained serum sodium to be within normal mammalian physiolog- ical limits. This, along with a net increase in sodium retention via the fecal and urinary routes, suggested that some factor was responsible for increased sodium stress during the interim. Analysis of porcupine winter foods, combined with a separate laboratory study, indicate that sodium levels in the natural foods were adequate to naintain a net sodium balance. In response to winter, porcupines were found to in- crease the relative medullary thickness of the kidney, increase urine osmolality and decrease fecal water content. This indicated that the porcupines were probably either undergoing water stress or using these neans to decrease water turnover rate. I would like to thank my advisor Dr. Richard W. Hill, who provi- ded lab space and equipment for this study, as well as valuable criti- cism at crucial nmments of this research. I also wish to thank the other menlbers of my guidance committee, Dr. Glenn I. Hatton and Dr. Rollin H. Baker for their assistance and generous lending of equipment. I express my gratitude to A. L. Bennett, M. Armstrong, and R. Leslie of Texas Gulf Sulfm: Inc. for permission to conduct the field portion of my studies on the Wilcox unit of Armstrong Forest. My appreciation is extended to the Michigan State Museum and the Zoology Department for partial support of this research. I especially thank my father who was my able field assistant and guide through all phases of my field work, and to my mother who didn't get too upset about finding porcupine quills in the living room. And lastly, I am indebted to that an'ry little ball of quills called the porcupine. TABLE OF CONTENTS ACKNOWLEDGEMENTS ....................... LIST OF TABLES ........................ Description of study area . . . ............ Field Study Methods .................. laboratory Study .................... RESULTS AND PRELIMINARY DISCUSSION .............. CONCLUSION .......................... LITERATURE CITED ....................... ii iv <2 9000on 42 52 LIST OF TABLES Table Page 1 Sodium and potassium concentrations of vegetation samples collected from the field and laboratory 19 sites ......................... 2 Seasonal values of porcupine necropsy data ...... 23 3 Seasonal values of serum sodium and potassium levels from field collected porcupines ............ 25 4 Summary of the laboratory study of sodium balance in captive porcupines held at room temperature and exposed to winter weather conditions ......... 37 5 Hematocrit, kidney RMI‘, urine osnolality and sodium retention abilities of captive porcupines ....... 40 iv LIST OF FIGURES Porcupine field study area ............... Laboratory animal collection site ........... Porcupine mean kidney weight vs. body length ...... Daily mam'mum and mininum temperature recorded from the outside holding enclosure ............. Bag 7 9 32 36 INTRODUCTION The survival of a mammal in the natural environment is dependent on its ability to maintain itself against environmentally adverse condi- tions . One such condition inherent to herbivorous mammals is that of limitation of sodium. In general, terrestrial plants do not require or accumulate sodium (Epstein 1972). Passive movement of sodium into vege- tation is often limited in regions where rainfall continuously leeches sodium from the soil and litterfall. Many terrestrial environments throughout the world have so little sodium that this ion may actually be a limiting factor to mammalian population size (Aumam 1965, Blair-West e_t_ a_]._. 1968, Jordan _e_t_ a]: 1973, Belovsky 1978). Animals deficient in sodium have been shown to seek the ion actively. Deficient darestic and laboratory animals select specifically for sodium (Danton and Sabine 1961) and have been shown to ingest pro- per quantities to regain sodium balance (Novakova and Cort 1966). Herbivores often search out mineral licks , apparently to obtain neces- sary amounts of dietary minerals, primarily sodium (Weeks 1978) . A seasonal spring peak in sodium appetite has been noted in a wide variety of herbivorous mammals: elk (Dalke e_t_ Q. 1965, Knight and Mudge 1967), deer (Weeks and Kirkpatrick 1976), motmtain goats (Hebert and Cowan 1971), moose (Botkin g a_l_. 1973, Jordan e_t §_1_. 1973) , rabbits (Blair-West e_t_ EE- 1968) , porcupines (Campbell and LaVoie 1967), woodchucks and fox squirrels (Weeks and Kirkpatrick 1978) . 2 The salt appetite noted is cannon to all ages and sexes, although it is undoubtedly influenced by pregnancy and/ or lactation. Various explanations to account for this seasonality of sodium appetite are all based on studies conducted on domestic animals. Frens (1958) has shown that a diet of new growth grass increased the fecal loss of sodium by cattle to a point where symptoms of sodium deficiency were detected. Suttle and Field (1967) working with sheep found that increased potassium content of forage and increased water intake could lead to sodium deficiency. These two factors have been repeatably cited to explain the spring peak in sodium appetite (Blair-West _e_t 31. 1968, Hebert and Cowan 1971, Weeks and Kirkpatrick 1976). An additional factor, which at this time has not yet been impli- cated in seasonal salt balance, is the effect of winter cold. labor- atory studies have shown cold exposure to have profound effects on salt and water balance. Fregley (1968) , working with rats, found that exposure to cold for 10 days resulted in dehydration of the body, coupled with a net loss of sodium and potassium. Identical results were observed by Neff (1966) in chipmunks. Ringens __e_t_: _al_. (1977) also noted a cold diuresis in tundra voles, but failed to measure sodium balance. In rats, dehydraticn appears to be maintained for as long as the animal remains in the cold cmditions (Box it _a_l_.. 1973, Fregly _el: al. 1976) . Field studies of seasonal body water camposition in shrews (Myrcha 1969) and black-tailed deer (Izmglmrst ti a1. 1970) corroborate these data. The literature is fairly confusing on the effects of cold ex- posure on the sodium concentration of body tissues. Only three pub- lications could be fomd addressing this subject. Clausen and 3 Storesund (1970) studying hibernating hedgehogs found a significant decrease in sodium concentration in liver and heart tissue, but a non- significant decrease in skeletal muscle. Yunosov and Gitel'men (1973) studied the effect of different environment temperatures on the re- distribution of potassium and sodium in rat tissues. At an environ- mental terperature of O—5° C the quantity of sodium in the majority of tissues dropped by 24.6-41.1‘70, but potassium changed little. Smith it _a_l_. (1978) fomd a significantly elevated sodium concentration in thigh muscle in winter-collected yearling male and juvenile and adult female snowshoe hares, versus those collected in surmer at a time of sodium stress. Three possible explanations can be proposed to explain a loss of sodium as a result of cold exposure. First, dehydration in itself would cause sodium loss, assuming that the sodium concentrations of tissues and body fluids remain at fixed physiological levels. Re- hydration results in sodium appetite when the animal atterpts to re- store the sodium required to maintain homeostasis (Fitzsimmons 1975). The use of the sodium pump has recently been shown to be an important means of elevating heat production in non- shivering thermo- geiesis of a variety of tissues (Ismail-Beigi and Ehdelman 1970, Horwitz 1973, Stevens and Kido 1974, Horwitz and Eaton 1977, Asano 91: 3;. 1976, Guernsey and Stevens 1977). The present belief concerning thermogenesis by active sodium transport is based on the hypothesis that, by some means, the membranes of the cells are made leaky to sodium and ATP is consumed in a futile cycle by purping sodium to maintain the normal concentration gradient. There may be a possible repercussion in utilization of this cycle leading to a net loss of sodium fram the body. Third, the stress of winter may be sufficient to complicate sodium retention abilities. It has been shown in voles (Aumann and leen 1965) that stress from increased population density influenced the various zones of the adrenal glands in such a way as to increase sodium loss from the body and increase sodium appetite. Cold exposure may affect the zones of the adrenal glands or other sites in the body important to sodium balance. The general aim of the present study is to determine the effect that cold exposure and natural winter conditions have on the salt balance of a mammal. To my knowledge, this is the first study of this kind to combine field measurerents with a simultaneous laboratory study. It was felt that documentation of the disturbances of salt and water balance resulting from cold exposure would shed light on overall yearly sodium balance. The animal clnosen for this study was the American porcupine, Erethizon dorsatum, for the following reasons. Most previous labora- tory studies on sodium and water balance have been done on rodents . Porcupines are strict herbivores, their winter food habits are well documented, and they are noted throughout the continent for an intense craving for salt. They also appear to be cold stressed in winter (Clarke and Brander 1973) . Ease of collection, size, and apparent ability to adjust to laboratory confinement (Bloam gt _a_];. 1973) also entered into this decis ion. The specific aims of the present study may be stated as follows: 1. To determine the effect that the natural winter environment has on the primary routes important to sodium balance. 5 Measured were: kidney size and concentrating ability, urine osmolality and sodium and potassium concentration, and fecal moisture and cation concentrations. To determine effects of winter on the sodium and potassium concentration of blood serum, liver and skeletal muscle. To determine the effect of cold exposure in the laboratory on overall sodium balance in the porcupine, and to assess this influence on the above mentioned body parameters. MATERIALS AND METHODS The investigation had two divisions. A field study was conducted which involved measurerents of various body parameters of wild-collected porcupines at two times of the year, prior to initiation of winter (November 10-25) and late winter (March 2-15) . Second, a laboratory study was performed on the effects of cold exposure on salt balance. Porcupines for this study were collected at the beginning of winter (December 21-23) and divided into two groups, the members of which were housed individually in outdoor and indoor enclosures , respectively. They were allowed to adjust to captivity for five weeks, after which precise measurements were taken on sodium balance of each animal for a 22-24 day period. At the completion of this monitoring period, the animals were autopsied and measured for the same parameters as in the field study. Description of Study Area The field portion of this study was conducted on the Wilcox Unit of Armstrong Forest lands (division of Texas Gulf Sulphur Company) in Elk and McKean counties of northwest-central Pennsylvania (see Figure 1). This region falls within the high Allegheny Plateau discussed by Rough and Forbes (1943). These forests were harvested around the ten of the century, and since then have progressed to a mature second growth forest, primarily canposed of beech, maple, hemlock and black cherry. Hemlock is generally confined to creek bottams, wet areas, ‘\ / \ A // \\ l \\ r/ \\ //(°o. \ ,\\‘l Ru" I / ’0‘ \ l 93‘" / ° \ | /’F‘- I ‘9 | / ‘ K ., , V I I I ’I 1 Buck R I U" I L—-——J 3 7, ‘¢ _McKeueeuTL. __ _. ELK COUNTY East Branch Clarion N I PENNSYLVANIA 0 (15 1 I l J C'— l _I Scale miles Figure 1. Porcupine field study area. 8 and north and east slopes. Porcupines abound on the study site. De- spite persecution and slaughter by local foresters, lumberman, trappers and hunters, the porcupine hold their own and were present during this study in populations estimated to be 30-40 animals per square mile. The laboratory animals were collected on areas approximately 15-20 miles southwest of the study site used in the field investigation. The area used falls within State Game lands no. 44 in central Elk County. See Figure 2. The two study sites were sufficiently close for the porcupines to be considered parts of the same breeding population (George M. Kelly, personal communication). Separate field and labora- tory sites were required because of the living habits of the porcupine. The laboratory-site animals resided in dens along dissociated rock outcrops. Nightly foraging trips from the dens were taken to and from feeding areas. Once an animal was tracked to its deming site, it could readily be caught in a leghold trap when it came out for the following night's activities. Porcupines on the field site resided in station trees throughout the year. This allowed daylight collection but prevented live trapping. Field Study Methods Porcupines were collected for field study with a twenty gauge slnotgun between the hours of 9:00 AM and 3:00 PM EST. Most animals collected in this manner were killed instantly. A total of 16 animals was collected in Noverber (4 juveniles, 6 pregnant females, 6 adult males) and 19 porcupines in March (7 juveniles, 6 pregnant females, 1 non-pregnant female, 5 adult males). A thorough autopsy was preformed on each animal. Immediately following death a blood sample was taken from each ELK COUNTY //‘ Squirrel Hollow I PENNSYLVANIA 0 0.5 1 'r i j Scale miles Figure 2. Laboratory animal collection site. 10 porcupine by deeply slicing the throat region with a five-inch stain- less steel skinning knife (R. H. Forschner Co. Switzerland). The blood flowed freely and was collected directly in three to six serological test tubes. During initial coagulation the clot was loosened from the mall by use of a nichrome innoculating needle. The sample was then left undisturbed to continue clotting. After a period of approximately 10 mnirmntes, a clear serum supernatant appeared. This liquid was poured off into a plastic vial, sealed with Scotch plastic electrician tape no. 88, and frozen for later analysis. Serum sodium and potassium con- centrations were measured using a Model 143 Flame Photometer (Instru- mentation laboratories Inc, Boston) with lithium as an interrnal standard. Simultaneous to the collection of the blood in the serological tubes, a sample was collected for micro-hematocrit measurement by use of Red Tip no. 2629-B Heparinized Capillary Tubes (Sherwood Medical Industries Inc.). Three to five tubes were collected from each animal, packed in clay, and prevented from being frozen in the field. The tubes were then centrifuged at 2000 rpm and the packed cell volume (PCV) noted. This speed was sufficient to pack the cells thoroughly, and duplicate readings were usually recorded from the same animal. When PCV readings varied slightly , they were averaged. Gross body data obtained at autopsy included the typical mam- malian museum measurerents, i.e. sex and reproductive status, total length, tail length, right ear and foot length, and total weight. The skull from each porcupine was cleaned, aged using criteria of Dodge (1967) and Earle (1978) , and preserved in the MSU Museum at East lansing (catalogue nos. 33032-33087). 11 Urine was collected directly from the bladder by use of a dis- posable plastic syringe. For storage, it was placed in a plastic vial, sealed with tape and frozen until analysis. Sodium and potassium con- centrations were measured on the Model 143 Flame Photometer. Because sodium concentrations were low, an initial dilution of only one to ten was required to measure this ion accurately. This solution was diluted additionally to obtain a reading on potassium. Osmolality of the urine was assessed with a Wescor Model 5100-A Vapor pressure Osmmeter. Readings were taken on all samples at one time to minimize machine fluctuations and human error. Data obtained from the kidneys included relative medullary thick- ness (RMl‘) , weight and moisture content. In the field the left kidney was utilized in measurement of RMI‘. This index to the renal concen- trating ability of the kidney was developed by Sperber in 1944, and is defined as: M = 10 (r) [(0 (h) (1)] ‘ 0'33 where t represents kidney thicknness, h is height, 1 equals length, and r stands for the radial extension of the medulla. The gross di- mensions of the kidney were obtained using a finely calibrated ruler. The kidney was then exposed by making a careful mid-sagittal cut with asharpknife such that themaximumareaof themedulla fromtlne cortical-medullary boundary to the tip of the renal papilla was visible. Five measurerents from the renal papilla to the cortical- medullary boundary were recorded and averaged to obtained the radial extension of the medulla. After these measurenents were taken, the kidney was placed in a pre-weighed vial , later weighed and stored frozen. At a later time the moisture content was determined on this 12 sample by drying to constant weight at 60° C (Napco Model 620 drying oven). Dnm'ing autopsy the right kidney was excised and placed in AFA re- agent (1070 formaldehyde, 10% glacial acetic acid, 30‘7o ethyl alcohol and 507° distilled water). It was anticipated that only a small difference in the RMI‘ measurerents might occur in the field-measured kidneys from the fall and late winter periods, in which case the fixed tissues were to be sliced with more precision in the laboratory with a microtane. However, examination of the data at the end of the field study indicated that a significant difference did occur between fall and late winter kidneys sectioned by hand. Therefore the fixed kidney of each por- cupine was used to obtain a second measurenent of RMI‘ for each animal by hand metlnods and the values averaged. The liver was excised during autopsy and placed in a pre-weighed ziplock bag. After return from a field day, the liver samples were weighed, all air was squeezed out, each bag was sealed in two ad- ditional heavy-duty plastic bags, and stored frozen. Sodium and po- tassium concentrations were measured on a cubic centimeter section of the tissue weighing approximately one gramn, which was cut from the central core of the liver. The sample was wet-ashed overnight in concentrated reagent-grade nitric acid and diluted appropriately to obtain readings on the ions. Moisture content was measured on a one-centimeter-thick central slice cut through the dorso-ventral plane of the liver. Skeletal muscle tissue was analyzed in much the same manner as liver. During autopsy a sample of skeletal muscle was collected from the Lpper thigh. All fat was trimmed off and the sample stored frozen 13 in a vial. A one-cubic-centimeter subsample was utilized to obtain ion concentrations by wet ashing. Moisture content was measured on the remaining tissue. During autopsy fecal samples were collected directly from the large intestine. This was accorrplished by severing the distal end of the colon and squeezing out a number of fecal pellets into a pre- weighed vial. The vial was then sealed and frozen until later analysis. Each sample was dried at 80° C to constant weight to obtain moisture content. Approximately two grams of the dried sample were placed in a clean Coors crucible, placed in a cold muffle furnace, brought slowly to 500° C and ashed for two hours. After cooling, 10 mnl of 6 molar HCl was added to the crucible containing the ash, heated to 100° C for 10 minutes, and filtered through a Whatmnan no. 42 filter paper into a 100 ml volumetric flask. The crucible and filtering apparatus were rinsed three times and the washings added to the flask, which was then brought to volume. From tl'e resulting solution sodium could be measured directly with the flame photweter, but a second dilution was required to read potassium. An additional factor important to the annual sodium balance of a ferale is the loss of sodium due to reproduction. In order to obtain a rough estimate of this loss, three fetuses and one placental complex were collected from the late winter period. These samples were cut at the imbilical cord and stored frozen within three layers of plastic bags. For analysis the materials were cut into smaller pieces and homogenized for five minutes in a clean Waring blender. A lS-gram subsample was extracted, placed on a disposable plastic petri plate and dried at 60° C for 48 hours to obtain average body moisture. 14 Two granns of this dried sarple were ashed for three hours at 550° C in a Coors crucible, dissolved in 15 ml 6 molar HCl and diluted to 1 liter. Sodium and potassium levels were obtained on this solution. Amniotic fluid from four porcnpines was also analyzed for these ions. All field specimens were roughly examined to estimate their para- sitic tapeworm and roundworm levels. This was accomplished by a visual inspection of the intestinal contents. Two sarples of tapeworms, approximately 20, probably Monoecocestus, were collected for sodium determination of the dried sarples. Because of the small size of the abundant neratodal parasite, probably Wellcomia, and difficulty in separation from intestinal contents, no ion determninations were at- terpted. Thirteen major food plant species were collected in the fall and winter periods. Bark tissue was collected from areas adjacent to recent feeding, by slicing bark with a stainless steel knife to fall directly into a plastic bag which was used in frozen storage. Hemlock foliage was sampled by collecting needles from branches in close proximity to those which had been clipped and the needles consumed, or by reroving the few needles remaining on the fallen branches. Ash and sodium and potassium concentratians were analyzed in the same manner as fecal sanples. Food species being utilized by each animal was noted by visual observation, but no atterpt was made to quantify amounts of foods ingested on a daily basis. laboratory Study PorCLpines used in the laboratory study were collected by use of no. 1 1/ 2 and no. 2 Victor coilspring steel leghold traps. Initially smaller traps had been tested, but these were found to be incapable 15 of holding the porcnpines. Transport of the mammals from the trap site to a waiting vehicle was accomplished by use of a holding cage (50 cm x 50 cm x 32 en, weight 14 kg) strapped to a backpack frame. In the case of there being two or more animals on a given trapping circuit, the additional porcnpines were carefully placed in bnm‘lap bags for transfer. Even 9 kilogram specimens were transferred by this latter method, although with extrene difficulty. The laboratory facility used in this study allowed porcupines to be maintained in two adjacent roams under different terperature con- ditions. (he half of the animals were kept inside under controlled terperature (18 : 3° C) and lighting (a 150 Watt flood larp was manually controlled to manual daylength). A second group was housed in an outside enclosure which was open to tie sky so that they encountered winter conditions. Tenperature was monitored with a Taylor maximum- minimum thermometer. All porcupines were housed individually in stainless steel cages, 90 cm x 60 cm x 32 cm (Unifab Corporation, Kalarazoo Michigan). Food and water were provided ad lib. in stainless steel bowls (11 cm in diameter and 8 cm deep). The food diet provided was modeled after a low sodium mixture formulated by Grace, et a1. (1979). The sodium concentration approximated the level found in the natural winter foods. The diet contained: 35% soybean meal, 30% coarse ground corn, 127° alfalfa meal, 12% coarse ground oats, 57.. wheat bran, 57.. corn oil, 17.. Ca003, 0.6% vitamnin D, 0.17.. methionine and 0.0257. vitamin A. Water was changed daily for the inside animals to prevent mnicrobial growth. Outside water containers were changed twice daily to allow access to liquid water in the subfreezing terperatures. 16 After a five-week period of adjustment, the flow of sodium through each porcupine was monitored for 22 to 24 days. This was accomplished by careful measurements on food consumption, and feces and urine pro- duction and sodium concentration. Porcupines were supported on coarse screen which permitted passage of fecal pellets and urine to a stain- less steel pan below. Urine was collected under mineral oil for the inside animals. In the outdoor enclosure, urine was allowed to freeze in the bottom of the pan and was thawed to obtain urine production data. Tests with control pans showed very little deliquescence to occur, and absolute values of sodium were unchanged. On a daily basis approximate- ly 30 m1 of urine and 15 gramns of feces from each animal were sampled, sealed in vials and stored frozen. Sodiumn concentration was determined on these sarples. Fecal moisture obtained on the subsarples was used to correct to dry feces production per day. From the beginning the laboratory study was beset with problems . During capture of the first porcupine on Decerber 21, one of the author ' 3 fingers mas broken . This severely hampered field operations , which only succeeded due to help of the author's father. After two additional trap nights the snow cover melted which made further trap- ping unprofitable. Fifteen animals were collected in the three-day trapping period but one escaped on Christmas eve . During transport of the animals to Michigan on Christmas Day, the fuel purp of the vehicle failed, forcing an unscheduled layover in Cleveland. This was probably most important because of the additional stress placed on the animals. After final transfer of the porcupines to Michigan State, one died of natural causes within two days and a second was dispatched because of a severe mange infection. Division of the renaining 12 animals left 17 six in each terperature regime. They were slowly adjusted from a diet of acorns obtained from the laboratory site to the artificial diet. Conversion required four weeks for eight animals , but the remaining animals never adjusted and ate no food diet during the entire study. Unfortunately, all four of these animals were from those maintained inside, leaving two as a sample size for this tenperature condition. Following conpletion of the monitoring period all porcupines were autopsied in the sane marnner as in the field study. Frozen samples from the autopsy were lost in a freezer malfunctiOn. As a result of the setbacks, the only information obtained from the laboratory study was: 1) Corplete salt balance data for eight por- cupines - six maintained outside, two maintained inside. 2) Data ob- tained during autopsy - organ weights , RMT values , and hematocrit. Statistical procedues involved use of the Stulent' s t test to evaluate differences between means. RESULTS AND PRELIMINARY DISCUSSION Porcupines on the field study site consumed a wide variety of tree barks during the fall, but by late winter generally restricted their diet to hemlock with only an occasional deciduous tree. The importance of hemlock in winter food consumption has been noted in a number of studies conducted in the hardwood-hemlock forests of the northeast (Curtis and Kozicky 1944, Shapiro 1949, Dodge 1967, Brander 1973, Earle 1978 and Kelly 1979). Hemlock is the preferred station tree (Curtis and Kozicky 1944), and the majority of the porcupines were collected from this species, 75% of the fall animals and 95% in winter. However, it was evident in the fall that porcupines would feed on adjacent de- ciduous trees as well as the hemlock in which they resided. Daring winter they often remain in the sane hemlock for a week, even up to a month (Silve, personal communication), feeding solely on this food source. This shifting to hemlock may be a result of the food quality value of that species (see Gill and Cordes 1972, for a discussion of porcupine food quality evaluation), or it may be due to difficulty of snow travel conpled with the energy savings of being stranded in an evergreen versus a deciduous tree (Clarke and Brander 1973). Data obtained from the vegetation analysis appear in Table 1. Sodium concentrations in bark tissues remain constant on a seasornal basis (likens and Bormann 1970, Day and lvbnk 1977), so data from fall 18 3830mm one 5 now do? COHHUHHOU hfimuommfi mfi so mom—5960 Eco p.83 omega .. a. 19 Hana N: m HHS moo .+. 85. m .. mama HmH 5 8% Re gone one} 3.3 H each 330593 «38832 H533 Hum: one H 958 «mama? amuse Head: Seem «NH H 258a lanes mamas H63 Sam N: H amp 305% mama. Hana No.3 8.3 H VHHB gear, 3ng Hum: H98 3:2 H H3 .558 .83. Hana 8.3 can H VHHB SE88 8% 392 3.2.. mom H vamp mHamufiamHHm 38mm HaHaN one: Sa H and SSH 333 He: Ram a: H VEB SHE/Hagan 5 Huge ale 5: H vamp «Enema 89E Heme a} a. mHam mac a A: a is mHHoaaHamm and H186 38 can H VHHB u8m .. .. HASH New? N: H aha .. .. Han: {H m. Rafi 2H .... a; a «.388 $98355 away +wz "be . an m me am H my a mHofim magnum H3 be wet/Ham: 4.3 be .3358: +V~ +1...z .mouam genome.” wow 3on $5 Eoum nouomfloo meQHHmm coauflmwg mo gaumflcouooo Swmmmuon mam aha—vow 2H 3an 20 and late winter samples were combined. The bark values presented in Table 1 can be used to estimate the sodium concentration of food items consumed from October to April, but no species distinctions can properly be made because of the small sarple sizes, the large number of factors which determine nutrient concentration both between and within a species (Srivastava 1964, Day and l’bnk 1977), and the sanpling schere used (Auchmoody and Greweling 1979) . The concentration of sodium in bark is generally higher than in herbaceous vegetation (likens and Bormann 1970 , Day and Monk 1977). However, even using bark data, porcupine food sodium levels on the field study site (Y = 6.6 mequiv/kg dry weight, n = 12) approximate those judged to be deficient in other studies con- ducted on sodium balance of herbivores: Blair-West et al. in 1968 (range 0.91 to 1.65 mequiv/kg dry weight); Hebert and Cowan in 1971 (X = 1.8 mequiv/kg dry weight); Weeks and Kirkpatrick in 1976 (range 1.68 to 4.47 mequiv/kg dry weight) and 1978 (range 0.61 to 9.1 mequiv/kg dry weight); Smith «35 a]: in 1978 (range 4.5 to 22.7 mequiv/kg dry weight). It must be mentioned that these studies judged an environment to be deficient in sodium based on research conducted with laboratory and domestic animals. Weeks and Kirkpatrick (1978) noted that the sodium reeds of wild fox squirrels and woodchucks are obviously lower , and the retension efficiency under normal conditions is higher than those of the laboratory rat, because mean sodium levels of almost all their plant foods are at least five to ten times lower than the minimum requirement for rats . Therefore, it is questionable if these en- vironments are deficient or merely low in sodium, especially since minimum requirements have not been established for wild species. High potassium concentration and a high potassium-to-sodium ratio 21 have often been considered more important to sodium balance in herbi- vores than actual food sodium concentration. Potassium concentration of tree bark is generally much lower than in herbaceous vegetation (Likens and Bormarmn 1970, Day and Monk 1977). Thus data obtained from this study on potassium concentration (range 33.2 to 114.3 mequiv/kg dry weight) and potassium-to-sodiun ratio (4.9 : 1 to 20.2 : l) of porcupine foods are lower than values from other studies, where po- tassium rnaged up to 680 mequiv/kg dry weight and the potassium-to- sodium ratio reached 60 : l to 295 : 1 (Weeks and Kirkpatrick 1976, 1978). Smith 3t 11. (1978) found levels of sodium, potassium, and the potassium-to-sodium ratio in snowshoe hare food to be almost iden- tical to those obtained in this study. Porcrpines obtained from the laboratory site were consuming almost exclusively acorns. This food source, which did not occur on the field study site, is low in sodium and high in potassium, resulting in an extrenely high potassium-to-sodium ratio (Table 1). Weeks and Kirk- patrick (1978) found similar values in acorns and used these data to explain a secondary peak in sodium appetite in fall observed in fox squirrels. However, they do not consider increased squirrel activity resulting from recently weaned animals, or the increased need for sodium in growth of juveniles, as alternate explanations of this fall peak. It was noted in this study that porcnpines collected from the laboratory site were extrenely fat, much more so than the field-site specimens . Two animals autopsied a week after capture had extrerely high levels of internal and subcutaneous fat, the latter being in excess of 2.5 cm thick on the lower back. In contrast, all field ll 22 specimens had little or no internal fat, and backfat neasurenents never exceeded 0.6 on in thickness. It appears that porcupines on the labor- atory site tolerate potential ion imbalance to feed on the nutritionally superior acorns. In addition to acorns it was noted that mnany porcupines actively sought and consured fronds of hay-scented fern (Dennstaedtia gmctilobula). This food item, while being high in potassium, is quite high in sodium, resulting in a favorable potassiLm-to-sodium ratio (Table 1). It is not known to what degree this food source supplerented sodium intake , since no measurenents were made of food quantities con- sured. Weeks and Kirkpatrick (1976) suggested that consurption of fungi, which are rich in sodium, supplerented intake of this ion in white-tailed deer. Peak consumption of fungi and animal matter in squirrels coincides with reproduction, lactation and peak sodium appetite (Bakko 1975, Weeks and Kirkpatrick 1978) . Jordan et _ai. (1973) studying moose on Isle Royale, concluded that were it not for sumer consumption of aquatic plants, which are 50 to 500 times higher in sodium than terrestrial foods, tlnese animals could not maintain a yearly balance of this ion. Dodge (1967) observed that large quantities of aquatic plants were consumed by porcupines in sumner, tlnough no importance was attached to this behavior. Data obtained from the autopsy of porcupines in the field study are summarized in Table 2. Each parameter will be discussed individual- 1y. In response to natural winter conditions a significant decrease in sodium concentration of serum and corresponding increase in potassium concentration was noted in the porcupines (Table 2). This was somewhat umou u m .uoooam mo om: H3 Hot/ma .8. 0 m5 um ugoamflcwaw powwow at.» noon u m .uCooBm «0 mm: can ago.” no. o one up unmoawflowwm powwow a 23 H: 3.0 H m0. 0H 3 RH H meme 0H 0:ng Hm: 233095 +e - Hz 2H H 0w. mm 0H m: H 8.3 0H 35ng 83 23.35 +2 .. H: 2.0 H 0m. 0H 0H 0m.0 H 2.00 0H H888 EH2 H. - H85 He H00 H 00.8 0H 2.0 H N20 0H 32ng Ha: 23585 e .. He N90 H 25H 0H HHH H 2.8 0H Gamma Has 2338.5 +2 - Ha 0H0 H 3% HH 8.0 H 00.2 0H H828 H32 H. .. 38:0 HfimHsHm mm.0H . H 0H.0H . H - Hr... H: H H. mmH HWH a. 3 H :8 0H 35ng b0 2\>u.wwe.+2 - r. 3.0 H N0. w HH S. H H NEH 0H mamas be wHHEHHama +2 .. H... 3.0 H 8. 3 HH 3. H H 8.2 H H888 .32 H. - H82 H: 0.3 H 3: 0 H.0H H H.0HH H 25:35 E .. as $0 H SH 0 00.0 H new H 355095 +2 - ...c... an” H 0% 0H Sm H 0H0 0 2328505 DHHmHsmo - HHS Hz 2.0 H 09R 3 2.0 H 0a.: 0H H828 has H. - H. 8.0 H $5 0H 8.0 H mum 0H H8832. Edam: H>HHHH2 - .0802 H... 0H...H H 20 2 mm. H H 500 0 HHH8HHBHH .. H... $0 H «0.: H 00. 0 H QHH 3 23:85 re .. r. Hum H H.0HH wH NH. H H .22 HH Hit/mama +2 - 083 Gm H we a firm H. my G on? .. 395m H853 82 HH2 .38 announced mafia—Hung mo 8ng Hmnommmm .N 3an 24 surprising considering that most mammals regulate these levels to be within fixed physiological limits. Division into separate sex and age groups shows variable response to winter (Table 3). Only juveniles and.pregnant females were found to have a significant decrease in sodium.concentration.and increase of potassium.concentration of serum. Juveniles would require extra sodium for growth (though no increase in 'mean juvenile weight was noted), and should cold exposure be a factor, they would be most cold-stressed.because of size. Pregnant females require sodinm for the developing fetus, placental conplex and amniotic fluid. NOn-pregnant females and adult males would be least stressed. The majority of laboratory studies on the effects of low salt intake and cold exposure on plasma electrolytes conclude that neither stress results in.any modification of plasma sodium or potassium.con- centrations (Bass and Henchel 1956, Coghlan.et_al: 1960, Kemg§t_§l. 1975) . Some researchers, however, have shown that a diet deficient in sodium can reduce the level of plasma sodium (Erdosova and Kraus 1976, Ybung §t_al: 1976). In response to cold exposure in rats, Hannon e§_al: (1958) feund a slight but significant increase in.the level of plasma sodium, but suggest that this was an artifact brought about by hemo- concentration. Baker and Sellers (1957), in contrast, found no change under similar conditions in the rat. Neff (1966) noted an immediate decline in plasma sodium and increase in potassium in cold-exposed chip- munks, reaching its lowest point on the fourth day of cold treatment. Though levels returned.to those of control animals by the end of the first week of exposure, at the end of the thirty-day-study, sodium concentration in plasma again fell below levels of control animals. Field observations of serum electrolyte concentrations are 33 M H.H8H.Bm Ho 8: HH HemH H00 an H HRHHHHHH 002:0 - rs HHS H HLBHHBm H0 mm: .3 HemH 8.0 mm H HRHHHHHH 82:0 - H. 60:meer Hosanna use mcowumaomno Hmsoog Mom ammo m @25an mo coaugendm Cmmav woo new 5.3000 93 fie» 82.580 mos mocmowmeawam r H» 25 He no H mm H 0.H H HHH 0 23285 +2 8.8m 8 as H 95 H H.H H HamH 0 HHHHEHHame +2 52 22 HHaa 0.2 H Hit/Heme .9 :22 38mm 0.HmH H 33:35 +2 gm HegemHHHé2 H 2. H H.0H 0 0.H H 0.HH 0 Hit/Hugo Eaten. mam—HEW r. an H 0.H: 0 NH H .HHHH 0 933020 +2 Sam Hammad H 0.H H 0.0.H H 0.H H mHH 0 23:35 la gm H 0.0 H H.00H H 3 H «.mNH m HHS/Hugo +2 8.3m HHHSBH. Amrm H .00 a Amm H W0 o 93an .. cowumowflmmflo .532 82 :2 .mmfinbouon @3838 3on Beam magma gwmmmuon one Since gm .uHo 83er Hmoommom .m 3an 26 somewhat limited. Again, most studies conclude no modification in the blood electrolytes result frcm low sodium enviroments or seasonality (Bakko 1975, Hebert and Cowan 1971, Weeks and Kirkpatrick 1976). Blair- West (31; a_l_. (1968) found a depressed concentration of plasma sodium (139 mequiv/l) in kangaroos from a low sodium environment versus one containing adequate sodium (148 mequiv/l). Smith gt; a_l. (1978) working with snowshoe hare found similar data in evaluating blood electrolyte levels during periods of sodium stress (April through July) caused by increased potassium-m-sodium ratio and potassium concentration of food items versus winter values (January through March). With the ex- ception of juvenile males, their data indicated that all age and sex groups had a lower sodium concentration in blood during periods of stress, though only in yearling males were the levels significant (144.3 mequiv/l in January to March versus 124.2 mequiv/l in April to July). Examination of their data indicates high levels of individual variation occurred, an observation likewise noted in porcupine measure- ments of this study. Packed cell volume of the animals in the field was shown to in- crease significantly from the fall to the winter (Table 2). The mag- nitude of this increase cannot be compared with other studies because of use of a non-standardized centrifuge, though methods used indicated a rise did occur. Sealander (1964) and Mclean and Lee (1973) both noted a seasonal peak in hematocrit occurring in winter. Withers gt _a_l_. (1979) found that arctic mammals have a higher hematocrit in relation to cmparab 1e tarperate-zone mammals or to the same species fram lower latitudes. Hagsten and Perry (1975) noted an increase in packed cell volume of lambs in response to a low sodium diet. 27 Porcupine urine osmolality was found to increase in winter rela- tive to samples collected in the fall, but no difference was noted in sodium or potassium concentrations (Table 2) . Very few researchers have made field measurements of trese parameters in salt-stressed herbivores. Blair-West e_t 31. (1968) monitored sodium and potassium levels in urine collected from sodium-stressed rabbits throughout the year. They fomd seasonal variation in urine electrolytes with a winter peak of sodium concentration (6 mequiv/l) relative to spring, summer or fall (0.59, 0.53, and 2.6 mequiv/ 1 respectively). No attempt was made to explain the seasonal variation in sodium concentration, but it was not correlated with potassium concentration, which was high in all seasons (range 209 to 466 mequiv/l). It is possible that seasonal change in food levels were responsible. Weeks and Kirkpatrick and Smith also noted low sodium and high potassium concentrations in field- collected urine during all seasons. White—tailed deer had urine sodium concentrations ranging from 0.4 to 7 mequiv/ 1, with potassium 160 to 230 mequiv/l (Weeks and Kirkpatrick 1976) . Snowshoe hares were fomd to contain urine sodium concentration below one mequiv/ 1 while po- tassium ranged from 23 to 305 mequiv/ 1 (Smith gt a_]_._. 1978). In an unprecedented study by Bakko (1975) , urine osmolality and potassium, sodium and urea concentrations in red and gray squirrels were monitored throughout the year. The peak sodium concentration of urine in red squirrels occurred in the January-February period (58.8 mequiv/l) with much lower levels in all other months (range 3.4 to 11.6 mequiv/ 1, means). Gray squirrels had elevated urine sodium from March through July (11.0 to 14.3 mequiv/l, means) in camparison to other portions of the year (3.4 to 8.7 mequiv/l, means). Bakko (1975) 28 suggested that the variation seen could be explained by variation in food items, though he did not measure this parameter. Peak osmolality of urine in red squirrels occurred in November—December and in gray squirrels March-April, though osmolality remained high throughout the year, except for July in both species. Potassium and urea were found to be the major solute constituemts. Both followed the same seasonal pattern as total urine concentration, but potassium was found to cor- relate much better with fluctuations in osmolality. Porcupine urine in the winter period had a higher osmolality than in fall, but no in- crease in potassium. Though urea was not measured, it is likely that this solute was responsible for the increase in osmnlality noted. It is apparent fram the meager data available in the literature that many more field studies will be required to understand the in- flueme of urine on salt and water balance in mammals. laboratory studies may be invalid in this endeavor, because as soon as a wild an- imal is placed in the laboratory, it is subjected to an artificial e1- vironment and its responses in such a situation may well mask features that are important for success in the natural elvirorment (Bellamy and Weir 1972, Bakko 1977). loss of sodium via the fecal route may well be more important to sodium balance in a mammal than sodium lost via the urine. Most laboratory studies on salt balance have neglected to monitor fecal loss of sodium (Grace e_t_: a_l_. 1979), though it has been shown that sodium levels in feces and urine normally decline during periods of sodium stress (JOnes §§_al, 1967). Though no change was noted in urine electrolyte concentrations , a decrease was observed in both sodium and potassium conceitration of feces (Table 2). This observation, along 29 with the modification in blood electrolytes , may indicate that some factor occurring between the fall and winter sampling periods created an increased need for sodium retention. No sex or age related dif- ferences were noted in the fecal electrolyte concentrations. The levels of ion constituents in winter (8.0 '3; 0.48 mequiv Na/kg dry weight and 135.4 1': 7.27 mequiv K/kg dry weight) were very close to those oc- curring in hemlock needles (9.4 i 1.5 mequiv Na/kg dry weight and 133.8 : 12.4 mequiv K/kg dry weight), which made up the bulk of the winter food. However, fall fecal concentrations (14.52 i 1.84 mequiv Na/kg dry weight and 234.7 '3: 15.8 mequiv K/kg dry weight) were higher than all bark values collected during this period (range 3.58 - 12.41 mequiv Na/kg dry weight and 33 - 114.3 mequiv K/kg dry weight). But because of lack of snowfall, porcupine movements could not be documented, and other food sources may have been responsible for the discrepancy of values. It is of interest to note that the ratio of the ions remains the same for each period. Smith e_t a_l_. (1978) in a small sample of snowshoe hare feces, found both sodium and potassium levels to be below mean plant levels, though the exact food items consumed in the formation of the feces were not documented. Fecal moisture has been shown to be very important in sodium loss via the fecal route . The spring shift to lush foods in herbivores results in a change in feces fram hard ch'y pellets to soft amorphous masses or to diarrhoea (Jordan e_t_ a1. 1973, Hebert and Cowan 1971, Weeks and Kirkpatrick 1976) and has been shown to cause an increase in sodium loss and even sodium deficiency (Frens 1958, Hebert and Cowan 1971, Weeks and Kirkpatrick 1976) . Porcupines in this study had well formed pellets in both seasons, but moisture content decreased 30 in winter (Table 2). Skadhauge e_t a_l_.. (1980) studied the effect of dehydration on the water content and electrolyte concentration in the feces of the dik-dik antelope. They found a reduction in fecal water content when the animals were dehydrated (56°. to 45% water), but found no change in fecal sodium or potassium concentration. Porcupines were found to have a similar reduction in fecal water content, but had a significant decrease in sodium and potassium concentration, which in- dicates an increase in sodium and potassium retention. In terms of sodiumn retention and potassium excretion, it would be more favorable to excrete excess potassium via the urine. The amount of sodium ultimately lost is dependent not only on the quantity of sodium per unit of urine and feces, but also the amount of each produced relative to food intake. Little is known of water tum- over rates in free-ranging wild animals, but it is generally agreed that water flux is 2-3 times greater in sunmer than in winter (longlmrrst g a1. 1970). Observations in the snow below station trees indicated that very little urine was produced, wlnile large quantities of fecal pellets littered the ground. Since almost all water intake must came fran the food source, it would appear that porcupines may be water stressed during prolonged stays in station trees during winter. Modifications of the kidney RMI‘ noted in this study may be in response to this water stress. Sclmidt-Nielsen and O'dell (1961) found a close correlation between RMI‘ and the ability to concentrate electrolytes in the urine. Changes in osmolality of urine and EMT (Table 2) observed in this study are consistent with this data. Can- parison of mean values suggest age and sex differences. Juveniles were found to have an 8.67.. increase in RMF, females a 9.4% increase, 31 and males a 4.37.. increase in winter. To my knowledge, no prior study has measured changes in relative medullary thickness in response to cold exposure in the laboratory or field. Bakko (1975) found that red squirrels inhabiting river bottcxns had a significantly lower RMI‘ value than those collected from upland coniferous and mixed hardwood habitats. laboratory studies have sham that any condition or treatment which brings about a requirerent for conservation of water results in an increase in RMI‘ (Blount and Blount 1968) . Exposure of porcupines to natural winter conditions caused an increase in the size of the kidney (Figure 3). Relative to unit body length, the mean kidney weight increased from the fall to winter period by 367.. in juveniles, 57.. inn adult and pregnant females, and 287.. in adult mnales. laboratory investigations of cold acclimation in mammals have shown an increase in kidney weight in response to cold to be a cannon phenamenon. In the pioneering work of Emery _e;t_ _al. (1940) , female rats experienced a 12.7% increase in kidney weight and males an 18.5°.. increase. Neff (1966) noted a progressive increase in kidney weight in response to cold exposure in chipmunks, reaching 307.. over control animals at the end of his 30-day study. Brown lemmings of both sexes experience a 107.. increase in kidney weight in responnse to cold exposure, but in varying lemmings under the same conditions, females were seen to increase 307.. and males only 177.. (Berberich and Folk 1976). The im- petus for increase in kidney size in response to cold exposure is unknown. Measurements of the sodium and potassium concentrations arnd water content of skeletal muscle and liver showed no significant seasonal differences (Table 2) . No difference was noted in liver weight, 32 .fiwcmH moon .m> unwwots .383 5.9: mfimeoouom .m madman 8 - Home: .69... [F - mm P I n - Ohm P b - I “W b - h - OI? - I I - mm b - - om 33:82. .-----------..w. .2 :2 x n . . . \ \mw . \ \ modemm 53¢ . . s \ .8 3mm “enauvnnn: moamcom mowmggafiwh . _\<. 353 - x" H822 X _ - x x _ \ \ moan: uHSon. an X . 3mm. \m H 18 \ x x o - .0 I I _l I II T (ox 8H2 884 kuQHB .. nov 1 8 - :nq ,eM Aaup'pl ueepq 33 though increase in liver weight has been noted in a number of studies of cold exposure in the laboratory (see Chaffee and Roberts 1971). Yunusov and Gitel'man (1974) reported severe modifications of sodium content in rat tissues when these animals were exposed to cold. They noted a decrease of 24 - 417. in sodium content of the majority of tis— sues (liver, kidney, thigh muscle, etc.) in comparison to a control group. No such modification was found to occur in porcupine tissues measured in this study. The porcupine is unique among small North American mammals be- cause of the length of the gestation period, which parallels that found in members of the Cervidae. Most females collected in Novem— ber were found to be in the early stages of pregnancy, as evidenced by corpora lutea, swollen uteri and young embryos. By March, the developing young had grown to approximately one third of their birth weight of 400 to 600 gramns (Shadle 1951). iny a single young is ever produced per fenale, but high fecundity is a rule. Fetus sam- ples collected for analysis weighed 166, 192 and 194 grams. Mois- ture content averaged 80.5 i 0.8 7., sodium concentration 78.8 i 3.5 mequiv/kg wet weight and potassium 42.2 i 0.4 mequiv/kg wet weight. The placental cunplex analyzed accompanied the 192-gram fetus and weighed 68 grams . Moisture content was 837., sodium con- centration 63.8 mequiv per kg wet weight and potassium 46.0 mequiv/kg wet weight. Four amniotic fluid samples showed a high de- gree of variability; the sodium and potassium concentrations in mequiv/l were: 76 and 6, 91 and 5, 80 and 6, and 134 and 10.5. No explanation is offered to qualify this high degree of variation though it may be an indication of the stress placed on females in 34 reproduction. Salt balance in porcupines may be complicated by their large para- site loads. Symons (1960) suggested that parasites inhabiting the in- testinal system could jeopardize sodium balance. During casual obser- vations in autopsy of field animals, it was noted that all animals were heavily parasitized with both Monoecocestus sp. and Wellccnmia sp. Fecal pellets often contained visible proglottids and whole adult roundworms. Curtiss and Kozicky (1944) examined nine porcupines in Maine and found a mean count per animal of 766 tapeworms (range 124 - 1528) and 2524 roundworms (range 353 - 5184). Olsen and Tolman (1951) estimated one porcupine they autopsied to contain 30,500 Wellcomia. Analysis of two tapeworm samples in this study found sodium con- centration to be 345 and 377 mequiv/kg dry weight. If a porcupine in the field contained 200 grams of parasite, the total sodium tied up in this matter would approximate 3.6 mequiv. This would be roughly equivalent to the sodium contained in 380 g of hemlock foliage, about two days consumption if absorptionn were 1007.. Since no study has docurented the turnover rate of tapeworms or ronmdworms in porcu— pines, no estimate can be made of their importance in sodium balance. Porcupines maintained in the outside holding enclosure used in the laboratory investigation appeared to be cold stressed. Pilo- erection was almost constant in all animals, and apparent shivering was noted on three occasions . The porcupines usually maintained the posture Clarke referred to as the ' lotus ' position, which is very effective at redncing heat loss through the poorly furred surfaces of tl'e thorax and abdomen, and protects the bare foot pads (Clarke 35 1969a). Daily maximum and minimum temperatures recorded in the enclo- sure are presented in Figure 4. The mean temperature for the 24-day study period was - 6.8° C (range - 16° to 5° C). Records obtained fran the National Climatic Center (National Oceanic and Atmospheric Administration, Ashville, North Carolina) indicate that no differ- ence exists between the October through March temperature profiles of lensing, Michigan and Ridgway, Pennsylvania. Clarke (1969b) recorded - 4° C to be the lower limit of the thermoneutral zone for porcupines collected in Massachusetts. In contrast, animals maintained in the inside enclosure expe- rienced little or no cold stress. After five weeks of captivity, one animal initiated a moult which continued until autopsy three weeks later. Only the wooly winter underfur was shed, no quills accanpanied the balls of fur collected frum the cage. A total of 52 grams of fur was collected, and the moult was not complete by autopsy. The stim- ulus for moulting could not have been day length, but light intensity and terperature may have been factors. No measurement was made of the sodium content of the fur, though this also may be relevant to salt balance. Franzman gt €11.- (1975) found sodium in moose hair to vary seasonally with an average of 34.7 mequiv/kg dry weight. Data fram the laboratory study on salt balance are summarized in Table 4. Information obtained from individual animals is presented in order to illustrate the large variation observed between animals. Porcupine food consunption compared favorably with that ob- served in a laboratory study by Bloan e_t _a_l_. (1973). They found daily consumption of Purina laboratory chow to be 135 - 150 grams daily for porcupines weighing 7.2 to 10.5 Kg. In this study, 36 6&5ng wfidaon mowmuoo m5 Ecum— umosouon 8.83.898”, 3.5.52 tam. gonna 3H3 .q madam erg Eh. flow fine 53 fin ”Ham ”Ham £3 ~HL_._H__P_.__.__pL__._.__r_...pp._—T_. _ . . u 0 O u D vomHl O _ O O O — O o . I u o noOHl m _ o e . . . m l . . . roml .o _ o _ m u . . . . H. “ voO m. QQHHme H€35 .V. o o . _ _ 10m ogmamgmugauo mflfimuuefiugauno 37 60:33 5538 so go 983 muggy: mmaomue £033 5 oofifle hwouNN .m Scum one $35.me mama n H... OO.O + OH ON.O NO OO.H OH.OH OO.H OOH OH.O «N ONH O.H O HHH: HHsO< NH HO.HH+ OO N¢.O OH H¢.H HO.HN OO.H OOH NH.O OO ONH O.O O «Hm: HHae< HH OH.H + NO OH.N OH HO.H OO.HH NH.H ON OH.O NH NO H.O O HHHamO .Om>:O OH NO.H - ON OO.H OO NN ON HO.ON NO.e HON H0.0 OO OOH H.O O HHHz HH=e< O OH.N + OO OO.O HO OH.OH OH.ON OO.N HOH OO.N HO OOH O.O O HHHz n HHOO< O OH.NH+ HO OO.O Oe OO.N NO.OH OO.O NHH O0.0 ON NOH H.O O HHMEHH N . mum HO.O - ON NH.O NO HH.H OO.O NN.H NO O.OO OH OH H.H H HHHEHH .woum 1» HH.O +. OO OO.N OH OO.H HH.HH OO.H HN OO.O OH OO O.O H . HHHz O .mfiuwocoo aged,» House,» on oomoexo one ofifimumflfiu :68 on Bus mofiesouoe HON/Human 5 woomHmn Egon mo bosom 3893an 93 mo gm .1» 0.33. 38 consumption ranged from 48 - 188 grams dry weight daily for 3.3 to 9.1 kg porcupines. Shapiro (1949) measured hemlock twig and foliar con- sumption to be 408 grams per day in a pregnant female (weight not given), but this figure represents wet weight and is only a rough approximation. Measurements of urine production from this study do not agree with the work by Bloom e_t 341: (1973) , who found urine production to be 347 to 371 ml per day. This discrepancy may be due to the difference in diet composition. Purina laboratory crow is 38 times higher in sodium than the diet provided in this study. The elevated water turn- over rate observed by Bloan and his colleagues may have been in re- sponse to potential salt loading. Though they did not measure sodium concentration of urine, Fregly (1968) observed in rats fed a similar diet, a urinary sodium concentration averaging 160 mequiv/l. This illustrates a point. Because of the food diet used in trust studies of salt balance, many comparisons with the state of animals in the wild are invalid. Even with the limited sample size of this study, comparison of the data obtained on food consumption and feces and urine production shows definite trends with the maintenance conditions. Daily food cmsumption of the outside animals was greater, averaging 26.3 g food/kg body weight compared to 17.8 g food/kg body weight in the in— side animals. This observation would be expected in light of the increased energy needs induced by cold exposure. The efficiency of food utilization in the outside animals was also greater; l9. 2% of the dry food intake was excreted as dry feces in the outside animals versus 24.2% in the inside animals. Urine production per gram food 39 intake was 0.93 ml in the outside animals, similar to 0.96 ml/gram food intake in the inside animals. Sodium conceitration of the feces was low in all animals except no. 4 (Table 4). Autopsy revealed that this porcupine was undergoing resorption of its fetus. Average sodium cmcmtratim of the feces in the remaining sevei animals was 6.53 mequiv/kg dry weight, slightly above the food sodium conceitration of 5.68 mequiv/kg dry weight. Urine sodium concentration was geierally low in all animals (Y = 2.01 mequiv/l), only slightly lower than in the field specimeis. Six of the eight animals in this study were able to maintain a positive so- dium balance in the presence of low sodium and high potassium levels in the food diet. Successful strategies included either low fecal sodium concentration or low urine conceitration or both. Because of inadequate sample size, no canparisons can be made between the cold- exposed and room-temperature porcupines in these regards. The limited autopsy data obtained from the laboratory animals are preseited in Table 5. Hematocrit was high in all animals, though the higher values were recorded fran the outside enclosure. Relative medullary thickness was relatively high in all animals, similar to values obtained from the March field collection. No increase in kid- ney weight was observed in either temperatm'e condition, all weights being similar to the Noverber field collection. The peak efficieicy of sodium retmtim while consmfing the laboratory diet was calculated to be 64 - 65% (Table 5). Urine osmolality was measured only on January 25 samples. Urine was collected within an hour of excretion, sealed and stored frozen. Osmolality was higher in all outside animals (Table 5) than field mound-Maw £585 on“ .3 nope/“Op Buomflxm OBOE...“ mo “.855. mg on mummmm .. On .N. NO O0.0 + OOOH ONO OO @388 mHmz “HOE NH .N. S HO.HH+ OONH OOO «388 3...: £23. HH .N. OO OON + OOOH OOO NN mafia OHQBO OHHEBH. OH NO.H - SHH HOO OO weaned 3m: #52 O .N. OO OH.N + «NHH OOO NO @338 «HO: “HOE O .N. «O OH.NH+ OOOH NN.O O.NN OOHOOOO mHmBO Ofiswfim N N0.0 - O0.0 OO OBOE flame 668mm O .N OO «HO + OOO OO 835 mHmz OHNBBO O OEHOBOQO 883m HON 83 amazes 888mg Seems 8383388 .02 SHOOO .N. Seem OVHN woe EH3 3&8qu “Oz b33058 83.3mm 8H»: .985 . $5938 63.”qu Oo OOUHHHOO 83:88 8%8 Ham .UHHOHQBO 3.9. 62 .882 .fiboumam .O «Heme 41 osmolality in either season (Table 2), though the composition of the food diet may have been a factor. Bakko (1977) noted a large dispar- ity between urine collected from red squirrels shot in the field (X = 309 nflsmoles/l) and those trapped and held in captivity for l - 3 hrs (X = 2074 n'Osmoles/l). CONCLUSION The spring peak in sodiun appetite has been attributed to the in- creased water content, potassium concentration and potassiLm-to-so- dium ratio of spring foods relative to those consumed in winter (Weeks and Kirkpatrick 1976, 1978). Although porcupine spring foods were not sampled in this study, earlier work by Leaf and Bicklehaupt (1975) in Armstrong forest can be used to estimate changes which occur in the spring shift from bark to foliage consumption. They measured sodium and potassium concentration of black cherry and sugar maple foliage for four surmers. When comparing their data to those obtained in this study, all ion concentrations are seen to increase in the spring shift (winter black cherry bark - 7.3 mequiv Na/kg dry weight and 58 mequiv K/kg dry weight, summer black cherry foliage - 16 mequiv Na/kg ck'y weight and 289 mequiv K/kg dry weight , winter sugar maple bark - 5.36 mequiv Na/kg dry weight and 50.1 mequiv K/kg dry weight, sunmer sugar maple foliage - 8 mequiv Na/kg dry weight and 174 mequiv K/kg dry weight). The ratio of potassimn to sodium also increases (black cherry bark 8:1 to 18:1 in foliage, sugar maple 9:1 in bark to 22:1 in foliage). Were this the extent of this study, conclusions similar to those of Weeks and Kirkpatrick (1976, 1978) may have been reached in order to explain the seasonal attraction to sodium. However, data obtained frcm the lab study indicate that porcupines are able to maintain sodium balance at levels of potassium as high as in the 42 43 spring foliage (292 mequiv K/kg dry weight in the food diet) and at a higher potassium-to-sodium ratio (51 : 1). Work by Grace e_t_ .11. (1979) showed that rabbits were able to adjust quickly to a change in the po- tassium-to-sodium ratio of 2 : 1 to 43 : 1, attaining near balance conditions in three days. In most if not all herbivores , increased potassium concentrations in spring foods do occur, but the influence this has on the sodium balance in the natural environment has not yet been substantiated. The attraction and apparent craving of porcupines to items con- taining salt has been noted extensively. In the natural emiron— ment they often consume discarded antlers (239 mequiv Na/kg in wlfite- tailed deer antlers, Weeks and Kirkpatrick 1976) or bones of dead cervids (130 i 18 mequiv Na/kg in moose bones, Botkin _e_t_: a_l_.. 1973) . Porcupines are best known for their incessant gnawing of man-made objects and structures containing the attractant (Spencer 1950, 1962, Dodge 1967). The use of salt on winter roads may also effect this behavior. Brander (in Earle 1978) noted increased porcupine roadkills and activity along roadsides from mid April to mid June. This coincides with peak sodium appetite in porcupines (Campbell and laVoie 1967) and may be related to the road licking behavior which Weeks and Kirkpatrick (1978) observed in this season in fox squirrels and woodchucks. Same investigators have suggested that sodium appetite may sim- ply be a cannon response of all mammals to the flavor of sodium and not be in response to sodium deficiency (see Denton 1967) . This argument can be discounted in porcupines by the work of Bloom et a1. (1973) who showed that when maintained on an adequate sodium diet, 44 porcupines exhibited a negative preference for solutions containing NaCl. Furthermore, they found that porcupines could distinguish be- tween deionized water and solutions at least as dilute as 0.5 mequiv. Na/l, which was the lowest level tested. The high degree of sodium attraction noted in porcupines is therefore probably in response to sodium deficiency coupled with their high responsitivity to sodium. To date, no researchers have attempted to qualify or quantify any specific plant feeding habit designed to obtain a higher intake level of sodium. Gill and Cordes (1972) suggested that fat content of food was very important in food species selection in the natural winter environment. Spencer (1950) noted a specific feeding pattern enabling porcupines to ingest bark containing higher levels of sugar. The microenvironmental changes among and within trees, as well as their individual status, would provide infinite variation in mineral con- tent of vegetation (Day and ank 1977, Aucl'moody and Greweling 1979) and tlms would caIplicate similar studies of this nature on sodium attractants. Dehydration in response to cold may have a major influence on the seasonal salt appetite. Water content of skeletal muscle, liver, and kidney in this study was not modified by the cold winter con- ditions, though total body water content was not measured. Longhurst et al. (1970) found that thigh muscle mnisture content of black- tailed deer also was not modified by winter, but found that the per- cent body weight as water changed significantly from 73. 57. in summer to 63.47. in winter. This indicates extracellular dehydration. In the laboratory, dehydration in response to cold has been observed in a mmmber of mammals , always accampanied by the loss of sodium 45 required to maintain hameostasis of body fluid composition (Fregly 1968, Neff 1966, Ringens 2; BA. 1977). This dehydration appears to be maintained in the cold (Box e_t 31. 1973, Fregly _e_1_: 31. 1976). Following extracellular dehydration, simple consumption of water which is low in sodium would be insufficient to rehydrate the body. When water is consumed, the body fluids become increasingly dilute, and water consumption must thus be stopped before fluid volume balance is restored. In this case, a sodium appetite is manifest, as the an- imal is attampting to restore not only the fluid but also the miner- als within it, sodium being the major ion (Fitzsimmons 1975). If the total body water in a white—tailed deer decreased as much as that measured by longhurst 91; a_l. (1970) , the sodium necessary for re- placement of isotonic body fluids in a 50—kg doe would be 12.3 grams, a considerable amount since only 19 grams is required for production of twin fawns in that species (Weeks and Kirkpatrick 1976). By using the data of Weeks and Kirkpatrick (1976) on deer food sodium levels for the period of March to May, and a rough estimate of daily food consurption of 2.0 kg/day, at 10070 efficiency, approxiamtely 105 days would be required to rehydrate the body. Indeed, the difficulty of increasing the body water pool may actually create a greater stress on sodium balance than reproduction, since it may occur in a shorter time span. The statement by Weeks and Kirkpatrick (1976) that in April there are "no intrinsic, suddenly imposed stresses cammon to all ages and sexes" may be mfounded. This study has demonstrated that no intracellular dehydration of tissues occurs in porcupines (Table 2) . Unfortunately, extracellular dehydration was not investigated, though, because of their sedentary 46 habits and ease of capture, porcupines would be excellent study an- imals for replication of work by Longhurst ti a_l_. (1970). Fregly e_t _a_l_. (1976) suggested that cold-induced dehydration may be beneficial for survival in the cold, but offered no mechanism. Ringens 25 a1. (1977) cited an obscure paper by Reader (1952) in.sug— gesting that thermal conductivity of tissues decreased with decreasing water content. The changes in the kidney noted in this study may be due to the probably water stress of porcupines, or primarily for reduction in ‘water turnover rate. Longhurst_§t.§l. (1970) measured a decreased water turnover rate in winter deer, 1.75 l/day in 33 kg animals, com- pared to 3.33 l/day in 32 kg animals in summer. Reduction in water turnover rate would benefit thermal balance, while at the same time possibly reducing sodium loss via the urine because of reduced.volume. The most available water source in winter is ice and snow. When one considers that this source must be melted and warmed to the temper- ature at Which it is lost, a process which.at - 10° C would require approximately 166 calories/g, the benefit of reduced water turnover rate is Obvious. The modification.in.hematrocrit noted in this study and others may also be in response to water stress combined with thermal stress. Fregly (1967) noted that evaporative'water loss from.rats is nearly doubled during exposure to cold. 'Withers et a1. (1979) calculated that expired air is a significant avenue of heat loss and can.comr prise 107. or mere of the metabolic heat production, even at low ambient temperatures. Blood with.higher hematrocrit and.hemoglObin content has a greater oxygen extraction ability and thus possibly 47 can reduce both heat and water loss (Withers g a_l_. 1979) . Thus the water, sodium and thermal balances of a mammal are inti- mately interrelated. It appears fram this study and review of the literature that sodium appetite would be greatest in spring. However, in the porcupine there appears to be a sodium stress in winter which is not caused by increased water intake, attelpts at rehydration or shifts in food diet which occurs at a later time. The cause of this stress can only be speculated upon. Neff (1966) noted that mechanisms responsible for the active restoration of sodium and potassium to normal levels, following modifi- cation occurring after cold exposm'e, were triggered only after suf- ficient violation of ion homeostasis. His data suggested that the sud- den alterations in metabolism resulting from acute cold exposure caused a temporary ion imbalance. This effect may be compounded by the continuous fluctuations of temperatme in the natural winter en- vironment. Throughout its range , the porcupine experiences temper- atures far below the recorded thermeneutral zone (the minimum terper- ature on one field collection day in Permsylvania was - 24° C), and a fluctuation of 30° C in a 24 hr period is not uncommon. In many areas, dens are not available, and occupation of station trees in- creases heat loss by wind and radiation. These conditions necessi- tate constant changes in metabolic rate, which may be the cause of the socium stress observed. The shifts in metabolic l'eat production which may cause ion im- balancemaybe due to theuse of the sodiumpump, whichappears tobe a means of increasing cellular thermogenesis (Himms-Hagen 1976). No research has been atterpted at monitoring sodium balance in a 48 continuously fluctuating environment, and thus the relationship be- tween cold exposure and sodium balance is mknom. Observations of porcupines in their natural winter environment, coupled with data obtained frem this study, provide an excellent op- portunity to estimate late winter sodium and water balance. During this time, porcupines are almost exclusively consuming hemlock foliage and bark. They often rerain for up to a month in this species as a station tree, during which almost all water must come from this food source. A small amount of water would be present in the form of snow, but much of the time this source is not available. If we assure in late winter that a 5 kg porcupine consuIes 200 g dry weight of hemlock foliage per day, a crude estimate can be made of the urine output and net sodium balance. The 200 grams of hemlock foliage (using Table 1) would contain 1.88 mequiv sodium and 26.76 mequiv potassium. If 207. of the dry food intake was excreted as dry weight feces, which data fram the lab study indicate is a good ap- proximation, using winter feces data (Table 2) , the daily 40 gram feces output would contain 5.42 mequiv potassium, 0.32 mequiv sodium, and about 40 ml water. The remaining potassium, which would exit the body via the urine, would require 191 ml of urine and contain 0.50 mequiv sodium (Table 2) . Net sodium gain, by these rough approxi- mations, would be + 1.06 mequiv/day, for an efficiency of 567.. No estimate of tie respiratory water loss in the porcupine exists, but at least 231 ml of water would be required daily for maintenance of this 5 kg porcupine. A similar computation was made using a daily food intake of 200 grams dry weight of hemlock bark. Fran this calculation, only 11 ml 49 of urine would be required to maintain equilibrium in potassium balance, and therefore approximately 51 ml of water would exit via feces and urine. The net sodium balance, while censuming 100‘7o hemlock bark would be + 0.196 mequiv sodium per day for 36% efficiency. These data can only attain relevance wl'm combined with an esti- mate of the sodium required in reproduction and yearly growth. The average birth weight of a porcupette has been recorded to be approxi- mately 500 grams (Shadle 1951) . Data collected from 11 fall-winter juvenile porcupines in this study shomd a mean weight of 2.65 kg, an increase of 2.15 kg over birth weight. Average fall-winter yearling might of 5 animals was 4.75 kg, an increase of 2.1 kg over juvenile might. Ten animals judged to be 2 1/2 years old were found to weigh 6.25 kg, an increase of 1.5 kg in body tissue. However, yearling fe- males may become pregnant, and the sodium required in reproduction would be roughly equivalent to 0.6 mequiv. By these data, it appears that the first three years of growth and reproduction would require sodium for production of 2.1 kg of body tissues per year. Beyond this age growth slows down and sodium stress would decrease. For mammals, sodium is a major canstituent, comprising about 0.15% of live body might. The value of 2.1 kg of body tissue would thus contain 137 mequiv of sodium. This quantity, if spread equally through the year, would necessitate a net requirexent of + 0.375 mequiv/ day. Fran the above calculations , it was shown that a porcu- pine consuming 200 grams ch'y might of hemlock bark per day, would only obtain 0.196 mequiv sodium and thus could not maintain sodium balance through the year on this food source. Hemlock foliage, at 50 + 1.06 mequiv/ day, would provide the necessary sodium required for growth. Analyzing the data obtained frum the necropsy samples there ap- pears to be a severe sodium stress imposed between the fall and late winter periods. This occurred in light of the diet composed primarily of hemlock foliage and the reduced growth rate in winter. Between the two sampling periods, some unknown factor must have acted upon the porcupines causing this sodium stress . By mid-winter the stress may have sufficiently threatened survival to a point where all efforts to retain sodium mre maximized. This could explain the efficiency noted by late winter in this study, and the high death rate in wintering juveniles (Smith 1977). At normal porcupine food consumption, many food sources would not contain adequate sodium to maintain a net balance with the environment. A porcupine consuming acorns with 64% efficiency in extracting sodium, would need to consume 600 grams dry weight of acorns per day, over three times normal consumption. Selective feeding, similar to that observed in moose by Jordan (1973) must definitely exist. The potential for sodium stress in the porcupine is very real. It has been shown in this study that cold exposure can affect sodium balance in many ways . The oumard manifestation of sodium deficiency in a mammal would most likely be reduced productivity and increased abortion. Shapiro (1949) suggested abortion was common in porcupines, though Dodge (1967) found little evidence of prenatal death (only two females of more than 200 autopsied had indications of resorption of the fetus). In this study, 10 adult field collected females in mid-term mre examined and one of these was in the process of 51 resorption. Because of high fecundity, in porcupines, net produc- tivity could easily be examined by total coverage of an area and comparison of the number of juveniles to adult females. Because of these easily measured parareters, their food habits and long gestation period, the porcupine would present a convenient sized analogue to the large cervids. Though certain problems do exist, as they do in all research, further investigation into the various aspects of sodium balance in the porcupine may prove to be very enlightening. LITERATURE CITED LITERATURE CITED Asano, Y., U. A. Liberman, and I. S. Endelman. 1976. Thyroid thermo- genesis. J. Clin. Inv., 57:368-379. Auchnmody, L. R., and T. Gremling. 1979. Problems associated with chemical estimates of bicmass. Northeastern Forest Experiment Station, Allegheny Naticnal Forest, Warren, Penna. 20 pp. Aumann, G. D. 1965. Microtine abundance and soil sodium levels. J. Mamm., 46:594-604. Aurann, G. D., and J. T. Emnlen. 1965. Relation of population density to sodium availability and sodium selection by microtine rodents. Nature, 208:198-199. Baker, D. G., and E. A. Sellers. 1957. Electrolyte metabolism in the rat exposed to a low enviremrental tenperature. Canadian J. Biochem. Physiol., 35:631-636. Bakko, E. B. 1975. A field water balance study of gray squirrels (Sciurus carolinensis) and red squirrels (Tamiasciurus hudsonicus) . Comp. Biochem. Physiol., 51:759-768. Bakko, E. B. 1977. Influence of collecting techniques on estimate of natural renal functian in red squirrels. Amer. Midland Nat. , 97:502-504. Bass, D. E. and A. Henshel. 1956. Responses of body fluid compartments to heat and cold. Physiol. Rev. , 36:128-144. Bellamny, D., and B. J. Weir. 1972. Urine composition of some hystri- comorph rodents confined to metabolism cages. Carp. Biochem. Physiol. , 42:759-771. Belovsky, G. E. 1978. Diet optimization in a generalist herbivore: the moose. Theor. Pop. Biol., 14:105-134. Berberich, J. J., and G. E. Folk, Jr. 1976. Cold acclimation in arctic lemmings. Carp. Biochenn. Physiol., 54:175-178. Blair-West, J. R., J. P. Coghlan, D. A. Denton, J. F. Nelson, E. Orcl‘ard, B. A. Scoggins, and R. D. Wright. 1968. Physiological, morphological and behavioral adaptation to a sodium deficient environment by wild native Australian and introduced species of animals. Nature, 217:922-928. 52 53 Bloam, J. C., J. C. Rogers, Jr., and 0. Maller. 1973. Taste respon- ses of the North American Porcupine (Erethizon dorsatum) . Physiol. Behavior, 11:95-98. Blount, R. F., and I. H. Blount. 1968. Adaptive changes in size of renal papilla with altered function. Texas Rep. Biol. Med. , 26:473-484. Botkin, D. B., P. A. Jordan, A. S. Dominski, H. S. Lowendorf, and G. E. Hutchinson. 1973. Sodium dynamics in a northern ecosystem. Proc. Natl. Acad. Sci., 70:2745-2748. Box, B. M., F. Montis, C. Yeomans, and J. A. F. Stevenson. 1973. Thermogenic drinking in cold-acclimated rats. Amer. J. Physiol. , 225: 162-165. Brander, R. B. 1973. Life-history notes on the porcupine in a hard- wozd-hemlock forest in upper Michigan. Michigan Academia, 5: 25-433. Campbell, D. L., and G. K. laVoie. 1967. Chemicals for porcupine control. Armnual Progress Report, Wildlife Research Work Unit F-45.2, Denver Wildlife Research Center. 7 pp. Chaffee, R. R. J., and J. C. Roberts. 1971. Tenperature acclimation in birds and mammals. Ann. Rev. Physiol., 33:155-202. Clarke, S. H. 1969a. Thermal energy exchange with the zenith by porcupines (Erethizon dorsatum) . Special Report, Dept. of Forestry and Wi Idl'ife Management, Univ. Massaclmsetts, Amherst, 40 pp. Clarke, S. H. 1969b. Thermoregulatory responses of the porcupine, Erethizon dorsatumn, at low environmental temperatures. Special Report, Dept. of Forestry and Wildlife Management, Univ. Mas- saclnusetts, Amherst, 61 pp. Clarke, S. H. , and R. B. Brander. 1973. Radiometric determination of porcupine surface temperature under two conditions of over- head cover. Physiol. Zool., 46:230-237. Clausen, G. , and A. Storesund. 1971. Electrolyte distribution and renal functian in the hibernating hedgehog. Acta Physiol. Scand. , 83:4-12. Coghlan, J. P., D. A. Denton, J. R. Coding and R. D. Wright. 1960. The control of aldosterone secretion. Postgrad. Med. J. , 36:76. Curtiss, J. D., and E. L. Kozicky. 1944. Observations on the eastern porcupine. J. Mamm., 25:137-146. 54 Dalke, P. D., R. D. Beeman, F. J. Kindel, R. J. Robel, and T. R. Williams. 1965. Use of salt by elk in Idaho. J. Wildl. Mgmt., 29:319-332. Day, F. P., and C. D. ank. 1977. Seasonal nutrient dynamics in the vegetation on a southern Appalachian watershed. Amer. J. Bot. , 64: 1126- 1139. Denton, D. A. 1967. Salt appetite. Pp. 433-459, _in Handbook of physiology, Section 6: Alimentary Canal, Volume 1: Control of Food and Water intake, C. F. Code (Ed.) Amer. Physiol. Soc., Wash. D. C., 459 pp. Danton, D. A., and J. R. Sabine. 1961. The selective appetite for Na+ shown by Na+ - deficient sheep. J. Physiol., 157:96-116. Dodge, W. E. 1967. The biology and life history of the porcupine (Erethizon dorsatum) in western Massachusetts. Unpubl. Ph.D. dissert. , Univ. Massachusetts, Amherst, 162 pp. Earle, R. D. 1978. The fisher-porcupine relationship in upper Michi- gan. Unpubl. M.S. thesis, Michigan Tech. Univ. , Houghton 113 pp. Emery, F. F.,, L. M. Enery, and E. L. Schwabe. 1940. The effects of prolonged exposm'e to low temperature on the body growth and on the mights of organs in the albino rat. Growth, 4:17-32. Epstein, E. 1972. Mineral nutrition of plants: principles and per- spectives. John Wiley & Sons Inc. , New York, 412 pp. Erdosova, R. , and M. Kraus. 1976. Effect of sodium intake on a1- dosterone and corticosterone production, the serum sodium con- centration and body weight in infant rats during weaning period. Physiol. Boheroslov, 25: 106 . Fitzsimons, J. T. 1975. Thirst and sodium appetite in the regulation of the body fluids. Pp. 1-7, in Control mechanisms of drinking (G. Peters, J. T. Fitzsimons, arnd L. Peters-Haefeli eds.). Springer-Verlag , New York. Franzman, A. W., A. Flynn, and P. D. Arneson. 1975. levels of some mineral elements in Alaskan moose hair. J. Wildl. Mgmnt. , 39:374-378. Fregly, M. J. 1967. Effect of exposure to cold on evaporative loss frum rats. Amer. J. Physiol., 213:1003-1008. Fregly, M. J. 1968. Water and electrolyte exchange in rats exposed to cold. Canadian J. Physiol. Pharmacol., 46:873-881. 55 Fregly, M. J., B. J. Kaplan. J. G. Brown, E. L. Nelson, Jr., and P. E. Tyler. 1976. Effect of water temperature druing cold exposure on thermogenic drinking in rats. J. Appl. Physiol. , 41:497-501. Frens, A. M. 1958. Physiological aspects of the nutrition of grazing cattle. Eur. Ass. Anim. Prod. Pub. 6:93-104. Gill, D. , and L. D. Cordes. 1972. Winter habitat preference of por- gngpines in the southern Alberta foothills. Canadian' Field-Nat, :349-355. Grace, S. A., K. A. Munday, and A. R. Noble. 1979. Sodium, potassium and water metabolism in the rabbit: the effect of sodium deple- tion and repletion. J. Physiol., 292:407-420. Guernsey, D. L., and E. D. Stevens. 1977. The cell membrane sodium pump as a mechanism for increasing thermogenesis during cold acclimation in rats. Science, 196:908-910. Hagsten, Ib, and T. W. Perry. 1975. Effect of dietary sodium levels on blood levels, urinary electrolytes and adrenal histology of lambs. J. Anim. Sci., 40:1205-1210. Hannon, J. P., A. M. Iarson, and D. W. Young. 1958. Effect of cold acclimation on plasma electrolyte levels. J. Appl. Physiol. , 13:239-240. Hebert, D., and I. M. Cowan. 1971. Natural salt licks as a part of the ecology of the mountain goat. Canadian J. Zool. , 49:605-610. ' Himms-Hagen, J. 1976. Cellular thermogenesis. Armn. Rev. Physiol. 38:315-350. Hough, A. F., and R. D. Forbes. 1943. The ecology and silvics of forests in the high plateaus of Pennsylvania. Ecol. Mnnogr. , 13:299-320. Horwitz, B. A. 1973. Ouabain-sensitive canponant of brown fat thermogenesis. Amer. J. Physiol., 224:352-355. Horwitz, B. A., and M. Eaton. 1977. Ouabain-sensitive liver and diaphragm respiration in cold-acclimated hamster. J. Appl. Physiol. , 42:150-153. Ismail-Beigi, F., and I. S. Endelman. 1970. Mechanism of thyroid calorigenesis: role of active sodium transport. Proc. Natl. Acad. Sci., 6:1071-1078. Jones, D. I. H., D. G. Miles, and K. B. Sinclair. 1967. Some effects of feeding sheep on low-sodium hay with and without sodium sup- plement. Br. J. Nutrit., 21:391-397. 56 Jordan, P. A., D. B. Botkin, A. S. Daminski, H. S. Lowendorf, and G. E. Belovsky. 1973. Sodium as a critical nutrient for moose ofltlzng Isle Royale. Proc. N. Amer. Moose Conference Workshop, 9: - . Kelly, C. M. 1979. Porcupines. Pemnsylvarnia For. Res. Coop. Ext. Ser. no. 69, 4 pp. Ken, D. C., C. Gomez-Sanchez, N. J. Kramer, 0. B. Holland, and J. R. Higgins. 1975. Plasma aldosterone and renin activity in dexanethasone—suppressed normal and sodium-depleted man. J. Clin. Endocrinol. , 40: 116-124. Knight, R. R., and M. R. Mudge. 1967. Characteristics of some natural licks in the Sun River Area, Montana. J. Wildl. Mgmt. , 31:293-299. leaf, A. L., and D. H. Bickelhaupt. 1975. Possible mutual pre- diction between black cherry and sugar maple foliar analysis data. Proc. Soil Sci. Soc., 39:983-985. Likens, G. E., and F. H. Bormann. 1970. Chemnical analysis of plant tissues from the Hubbard Brook Ecosystem in New Hampshire. Yale Univ. Sch. Forest. Bull. 79. pp 1-25. longhurst, W. M., N. F. Baker, G. E. Cormolly, and R. A. Fisk. 1970. Total body water and water turnover in sheep and deer. Amer. J. Vet. Res., 31:673-677. Maclean, G. S., and A. K. lee. 1973. Effects of season, tenperature, and activity on some blood parameters of feral house mice _(ME musculus). J. Mamm., 54:660-667. Myrcha, A. 1969. Seasonal changes in caloric value, body water and fat in some shrews. Acta Theriol. , 14:211-227. Neff, W. H. 1966. Sodium and potassium levels in serum and urine of cold-exposed chipmunks. Unpubl. Ph.D. dissert. , Pennsylvania State Univ. , State College, 77 pp. Novakova, A., and J. H. Cort. 1966. Hypothalamic regulation of spontaneous salt intake in the rat. Amer. J. Physiol. , 211: 919-925. Olsen, 0. W., and C. D. Tolman. 1951. Wellcomia evaginata (Smitt 1908) (OxyuridaezNenatoda) of porcupines in mule deer , Odocoileus hemionus, in Colorado. Porc. Helm. Soc. Wash., Reader, S. R. 1952. Effective thermal conductivity of normal and rheumatic tissues in response to cooling. Clin. Sci., 11:1-12. 57 Ringens, P. J., G. E. Folk, and J. J. Berberich. 1977. Cold ac- climation in the tundra vole. Acta Theriol., 22:67-74. Schmidt-Nielson, B. , and R. O'dell. 1961. Structure and concentra- ting mechanism in the mammalian kidney. Amer. J. Physiol. , 200: 1119- 1124 . Sealander, J. A. 1964. The influence of body size, season, sex, age and other factors upon some blood paraneters in small mam- mals. J. Mamm., 45:598-616. Shadle, A. R. 1951. laboratory copulations and gestations of por- cupine Erethizon dorsatum. J. Mamm., 32:219-221. Shapiro, J. 1949. Ecological and life history notes on the porcupine in the adirondacks. J. W., 30:247-257. Skadhague, F., E. Clemens, and G. M. 0. Maloiy. 1980. The effects of dehydration on electrolyte concentrations and water content al the large intestine of a small ruminant: the dik-dik ante ope. J. Comp. Physiol., 135:165-173. Smith, G. W. 1977. Population characteristics of the porcupine in northeastern Oregon. J. Marm., 58:674-676. Smith, M. C., J. F. Leatherland, and K. Myers. 1978. Effects of seasonal availability of sodium and potassium of the adrenal cortical function of a wild population of snowshoe hares, ljpgs amnericanus. Canadian J. Zool., 56:1869-1876. Spencer, D. A. 1950. Porcupines-rarinling pincushions. Nat. Geo- graphic, 98:247-264. Spencer, D. A. 1962. The porcupine, its economic status and con- trol. Fish and Wildlife Service, Dept. of Interior. , Wildlife leaflet 328. 7 pp. Sperber, I. 1944. Studies on tl'e mnamnalian kidney. Zool. Bidrag. Fran Uppsala, 22:249-431. Srivastava, L. M. 1964. Anatomy, chemistry and physiology of bark. Pp. 203-277, in International Review of Forestry Research, Vol. 1 (J. A._R'amberger and P. Mikola, eds.). Academic Press, New York, New York, 404 pp. Stevens, E. D., and M. Kido. 1974. Active sodium transport: a source of metabolic heat during cold adaptation in mammals. Comp. Biochem. Physiol., 47:395-397. Suttle, N. F., and A. C. Field. 1967. Studies on magnesium in run- inant nutrition. 8 . Effect of increased intakes of potassium and water on the metabolism of magnesium, phosphorus, potassium and calcium in sheep. Br. J. Nutrit., 21:819-831. 58 Symons, L. E. A. 1960. Pathology of infestation of the rat with Nippostrongylus muris. Australian J. Biol. Science, 13:171-183. Weeks, H. P. , Jr. 1978. Characteristics of mineral licks and be- havior of visiting white-tailed deer in southern Indiana. Amer. Midland Nat. , 100:384-395. Weeks, H. P., Jr., and C. M. Kirkpatrick. 1976. Adaptations of white-tailed deer to naturally occurring sodium deficiencies. J. Wildl. Mgmt., 40:610-625. Weeks, H. P., Jr., and C. M. Kirkpatrick. 1978. Salt preferences and sodium drive phenology in fox squirrels and woodchucks. J. Mamm., 59:531-542. Withers, P. C., T. M. Casey, and K. K. Casey. 1979. Allometry of respiratory and haematological parareters of arctic mammals. Comp. Biochem. Physiol., 64:343-350. Young, D. B., R. E. McCaa, Y. J. Pan, and A. C. Guyton. 1976. Ef- fectiveness of the aldosterone-sodium and potassiumn feedback control system. Amer. J. Physiol., 231:945-953. Yunusov, A. Y., and E. I. Gitel'man. 1973. Changes of the potassium and sodium content in some rat tissues in relation to environ- mental temperature. (fram Abstract). Uzb. Biol. Zh., 17:69-70. “nnnmnmm