Roads are a mortality source for federally threatened eastern massasauga rattlesnakes (EMR; Sistrurus catenatus) in Michigan, yet we lack a clear understanding of EMR space use and habitat selection near roads. Identifying when, where, and why EMR use spaces near roads could inform decisions to reduce risk of road-related mortalities. Objectives of this research were to survey for EMR at sites along roadsides, report on occupancy probability, demonstrate how weather influences EMR visibility during visual encounter surveys, and explore environmental factors resulting in high EMR space use near roads. During 54 surveys (following previously published survey protocol) 35 sites, five EMR were detected at two distinct sites. Individual EMR surveys had low site-level detection probability (mean = 0.16 (SE = 0.11)), but repeated surveys increased detection probability to near 1.00 at some sites, and visual encounter surveys should be conducted during optimal temperature ranges (~30-40° C in this study). The 24 telemetered EMR at occupied sites were relocated 1-5 times per week, and the percentage of body visible and burrow use was recorded. Body exposure and burrow use were modeled with a Bayesian beta regression to discern when EMR are most visible in active season (April-October; 2020-2022). Estimated body exposure ( ̄x = 42%, SE = 3%, range = 0-100%) increased from ~25% exposure at ~15° C to ~55% at ~40° C. Probability of burrow use was related to Julian day broadly represented the transition from inactive to active seasons, with low probability of use (<0.10) from June to August. Male EMR were less likely ( ̄x = ~0.02%, range = ~2 - 4%) to use burrows than females ( ̄x = ~8%, range = ~2 - 42%). Brownian Bridge kernel home ranges for four (3 – female, 1 – male) telemetered EMR with ≥20 relocations were combined into a single spatial layer representing intensity of snake use. A Bayesian beta regression model predicted intensity of snake use based on environmental covariates. At Site 1, probability of use was greatest ≥70m of the road and correlated negatively with canopy cover (use decreased from 45% at 0% canopy cover to 20% at 90% cover). At Site 2, EMR probability of use increased by 5% (42% to 47%) as distance from the road approached 100m, but use declined sharply by 23% (50% to 27%) approaching 300m from the road. Core use areas for EMR were close (e.g., ≥20 m) to roads, likely due to vegetation management (e.g., mowing), and the physical properties of the roadbed (i.e., warmer below ground temperatures).
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