Detection of American alligators in isolated, seasonal wetlands

Abstract

Although the American alligator has been well-studied in coastal marshes and large reservoirs, very few studies have taken place in the isolated, seasonal wetlands that occur within the inland portion of the alligator’s range. Understanding alligator populations in these systems is important because, although they are subject to the same management strategies and regulations as their more well-studied counterparts, they may have markedly different population dynamics and densities. Additionally, understanding patterns of alligator presence in isolated, seasonal wetlands is important to understanding how alligators may affect these critical habitats as ecosystem engineers. However, survey methods designed for large, open water systems may not work in these small, vegetated wetlands, and their efficacy in this habitat has yet to be documented. We conducted eyeshine surveys for alligators along walking transects through isolated, seasonal wetlands in southwest Georgia. We used a double-observer method with a Huggins closed capture analysis to determine the detection probability of this method, to model the effects of observer and wetland type on that parameter and to estimate abundance. We found that detection probability for eyeshine surveys under the best-supported model was 57%, between 2 and 5 times higher than documented in other habitats. We then compared eyeshine surveys with systematic trapping to ascertain which components of the population were more likely to be detected by each method. Both methods were effective in detecting a range of size classes in the wetlands; however, the two methods were most effective when used in concert. Wildlife biologists studying population trends and establishing harvest quotas can use this information to design surveys in the inland portion of the alligator’s range. © Koninklijke Brill NV, Leiden, 2009