Fallen Nestlings and Regurgitant as Mechanisms of Nutrient Transfer from Nesting Wading Birds to Crocodilians


Positive interspecific interactions can shape fundamental wetland ecosystem dynamics, including energy transfer and spatial distribution of nutrients. Birds, by foraging in one location and nesting in another, commonly act as between-ecosystem nutrient vectors. However, the distribution of nutrients within nesting areas and mechanisms of transfer to other trophic levels are poorly understood. We report on measurements of available food transferred from nesting long-legged wading birds to American alligators (Alligator mississippiensis) in the Everglades of Florida, USA. Using throughfall traps, a historic dataset on nesting success and a literature-parameterized alligator energy budget, we estimated the potential food available to alligators via regurgitant and nestling carcasses, and compared that to alligator food requirements. Although dropped regurgitant is of little importance to scavenging alligators, we estimate that nestling carcasses throughout the ecosystem could support the energetic requirements of hundreds of alligators for periods of several months. This resource occurs during the dry season, when alligator thermoregulatory opportunities are relatively scarce and female alligators are mobilizing resources for egg-laying. Our results indicate that through fallen nestlings, wading bird nesting colonies have strong potential to benefit alligators. This facilitative exchange may be globally widespread, forming a keystone process in many tropical and subtropical wetlands.