Evidence of intrapopulation differences in rattlesnake defensive behavior across neighboring habitats

Frequent human encounters, even if benign, can influence fight-or-flight decisions in animals. Understanding how these responses are linked to human activity provides important insight into the ecology and conservation of populations, particularly those that may interact with humans. To this end, we compared the defensive behavior (rattling) of rattlesnake populations at two study areas containing habitats with contrasting levels of human activity. Immediately after capture in the field, we subjected rattlesnakes to the approximation of an approaching hiker and recorded the distance that they first rattled. To accommodate for zero inflation in our analysis, we developed a two-part model. We first assessed the probability of rattling occurring via a logit model, followed by a log-normal regression model to assess the distance to initiation of rattling as affected by covariates (site, temperature, time of year, snake size, etc.) for all non-zero values. Snakes occupying areas subject to high levels of human activity allowed investigators significantly closer before rattling (P < 0.001). Compared to areas of low human activity, these snakes were 6.17-7.61 times less likely to engage in rattling behavior at all. We argue that the uniform response recorded among rattlesnakes in areas of high human activity suggests population-level habituation to human presence. The behavioral differences we detected over relatively short distances have implications for land management, including the impacts of recreational areas with a high degree of human activity. Our findings are consistent with studies of other taxa on the impact of human activity on animal behavior, suggesting this pattern may be widespread. Significance statement The influence of human activity on the behaviors of wildlife is difficult to quantify but of significance for conservation and management. We studied how the defining defensive behavior of rattlesnakes, tail rattling, differs according to environmental conditions. Rattlesnakes in areas of high human activity displayed a highly uniform, muted response to an approaching investigator when compared to snakes in areas of negligible human activity. Our results suggest that the level of human activity on a landscape may influence the expression of a core behavior in rattlesnakes, and that behavioral shifts may become evident in habitats subject to contrasting levels of human activity within a relatively short period of time. With replication, this type of survey could serve as a less costly alternative to traditional population impact studies for rattlesnakes.

Automated summary

Frequent human encounters can influence fight-or-flight decisions in animals. This study compared the defensive behavior of rattlesnake populations in areas with contrasting levels of human activity, finding that snakes in high human activity areas displayed a more muted response to approaching humans compared to snakes in low human activity areas.