Impact of censusing and research on wildlife populations

Abstract

Population monitoring and research are essential for conserving wildlife, but these activities may directly impact the populations under study. These activities are often restricted to minimize disturbance, and impacts must be weighed against knowledge gained. However, few studies have quantified the effects of research or census-related visitation frequency on populations, and low visitation rates have been hypothesized to have little effect. Hibernating bats have been hypothesized to be especially sensitive to visitation because they have limited energetic stores to survive winter, and disturbance may partly deplete these stores. We examined the effect of site visitation frequency on population growth rates of three species of hibernating bats, little brown bats (Myotis lucifugus), Indiana bats (Myotis sodalis) and tri-colored bats (Perimyotis subflavus), both before and after detection of the disease white-nose syndrome. We found no evidence that more frequent visits decreased population growth rates for any of these species. Estimated coefficients were either the opposite sign as hypothesized (population growth rates increased with visitation frequency) or were very small (difference in population growth rates 0.067% [SE 2.5%]–1.8% [SE 9.8%]) relative to spatial and temporal variation (5.9–32%). In contrast, white-nose syndrome impacts on population growth rates were easily detected and well-characterized statistically (effect sizes 4.4–8.0; severe population declines occurred in the second and third years after pathogen detection) indicating that we had sufficient power to detect effects. These results indicate that visitation frequency (for M. sodalis: annual vs. semi-annual counts; for M. lucifugus and P. subflavus: 1–3 three research visits per year) had undetectable impacts on bat population growth rates both with and without the additional stress of an emerging infectious disease. Knowledge gained from censuses and research may outweigh disturbance due to human visitation if it can be used to understand and conserve the species.