Body size measurements and stomach contents of Alligator mississippiensis on Jekyll Island, Georgia

Human-driven land use change can fundamentally alter ecological communities, especially the diversity and abundance of large-bodied predators. Yet despite the important roles large-bodied predators play in structuring communities through feeding, there have been only a few investigations of how the feeding patterns of large-bodied predators change in human-dominated landscapes. One group of large-bodied predators that has been largely overlooked in the context of land use change is the crocodilians. To help fill these gaps we studied the feeding patterns of juvenile American alligators (Alligator mississippiensis) on neighboring barrier islands on the southeast coast of Georgia, USA. Jekyll Island has multiple golf courses and substantial amounts of human activity, while Sapelo Island does not have any golf courses and a much smaller amount of human activity. We found that juvenile alligator populations on both islands ate the same types of prey but in vastly different quantities. Sapelo Island alligators primarily consumed crustaceans while alligators that lived on Jekyll Island’s golf courses ate mostly insects/arachnids. Furthermore, the Jekyll Island alligators exhibited a much more generalist feeding pattern (individuals mostly ate the same types of prey in the same quantities) than the more specialized Sapelo Island alligators (diets were more varied across individuals). The most likely explanation for our results is that alligators living on golf courses have different habitat use patterns and have access to different prey communities relative to alligators in more natural habitats. Thus, land use change can strongly alter the feeding patterns of large-bodied predators and, as a result, may affect their body condition, exposure to human-made chemicals, and role within ecological communities.

Methods
We conducted the study on Jekyll Island (31° 3’58” N, 81° 24’52” W), a barrier island on the southeast coast of Georgia, USA between March and August during 2019 and 2020. We located alligators on golf courses at night using handheld spotlights and captured them using a fishing pole and line with a modified treble hook attached. We then brought each animal to shore and taped its mouth closed before measuring total length (TL) and snout-vent length (SVL) dorsally to the nearest 0.1 cm. We determined sex via cloacal examination and then used the hose-Heimlich technique to collect stomach contents. This technique involves filling each alligator’s stomach with water and then applying pressure to the alligator’s flanks until the water, and any prey items inside, exit the mouth. We collected all water and prey items in a bucket and, following release of each alligator at the capture site, we sieved the prey items and stored them in jars filled with 95% ethanol. In the laboratory we identified all prey items to the lowest possible taxonomic level and weighed each item to the nearest 0.1 g (wet weight).