Evaluating the conservation and agricultural applications of orchard nest boxes for a declining raptor

Human activities over the past 50 years have caused changes in ecosystems that have led to gains in economic development at the cost of biodiversity loss and degradation of ecosystem services, the functions and processes of ecosystems that benefit human well being. For example, agricultural expansion and intensification has degraded wildlife habitat by removing sources of nesting and roosting cavities, particularly mature trees, which can negatively affect abundance and diversity of animal taxa that provide regulating ecosystem services, such as pest reduction. Many cavity-dependent species will use nest boxes in areas where natural cavities are scarce, thus nest boxes are an easily implemented landscape enhancement. In this dissertation, I drew from theoretical frameworks of population dynamics, foraging ecology, parental care, and predator-prey interactions to assess the potential benefits of nest boxes in terms of conservation of a declining raptor and enhancement of pest reduction services in a fruit-growing region. Although the American Kestrel (Falco sparverius) is the most common falcon in North America, multiple monitoring programs have detected significant and widespread population declines. While the causes of these declines at the continent-wide scale are not yet understood, at the local scale, many breeding kestrel populations are limited by availability of nest sites. In Chapter 1, I monitored 18 new nest boxes installed in cherry orchards (Prunus spp.) in northwestern Michigan and found that kestrels made nesting attempts in 100% of the boxes and showed high reproductive rates. Furthermore, models of daily survival rates for nests and brood size at fledging for successful nests indicated that kestrels were highly tolerant of both traditional monitoring techniques (opening the box) and newer camera technologies (a pole-mounted video camera and nest-box video cameras). In Chapter 2, I used roadside transect surveys and multi-season occupancy modeling to determine that the installation of nest boxes has increased the presence of kestrels in the region between 2013 and 2016. Chapters 1 and 2 indicate that orchard nest boxes can benefit the local conservation of kestrels by increasing breeding populations, which may in turn benefit agriculture by promoting kestrel presence, and therefore predation on pest species, in and around orchards. In Chapter 3, I used nest box video cameras to determine that kestrels provision their nestlings with known orchard pests, including grasshoppers, voles, and frugivorous birds; furthermore, I observed generalizable trends in kestrel prey removal based on nestling age, seasonal timing of prey availability, brood size and sex ratio, weather, and adult female movements relative to the nest box. In Chapter 4, I used transect surveys to determine that fruit-eating bird counts were lower in orchards with active kestrel nest boxes, thus kestrel activity associated with nest boxes likely acts as a reliable cue of predation risk that, in combination with direct consumption, reduces fruit-eating bird abundances in orchards. Finally, in Chapter 5, I used live-trapping to determine that summer small mammal abundances were lower in orchards with active kestrel boxes and orchards that had been more recently mowed; however, these differences did not carry over as differences in winter presence in orchards, when mammal damage to trees is most likely. Based on the results, I recommend that future projects utilize a consistent surveying protocol across seasons, conduct winter surveys in orchards without rodenticide use, and combine small mammal surveys with fruit and tree damage assessments in order to identify which species are responsible for damage throughout the year and under different conditions (e.g., with variation in snowfall).