Alligator presence influences colony site selection of long-legged wading birds through large scale facilitative nest protector relationship

Abstract

Positive ecological relationships, such as facilitation, are an important force in community organization. The effects of facilitative relationships can be strong enough to cause changes in the distributions of species and in many cases have evolved as a response to predation pressure, however, very little is known about this potential trend in vertebrate facilitative relationships. Predation is an important selective pressure that may strongly influence breeding site selection by nesting birds. The American Alligator (Alligator mississippiensis) facilitates a safer nesting location for wading birds (Ciconiiformes and Pelecaniformes) by deterring mammalian nest predators from breeding sites. However, alligators do not occur throughout the breeding range of most wading birds, and it is unclear whether alligator presence affects colony site selection. We predicted that nesting wading birds change colony site preferences when alligators are not present to serve as nest protectors. Within the northern fringe of alligator distribution we compared colony characteristics in locations where alligator presence was either likely or unlikely while controlling for availability of habitat. Wading birds preferred islands that were farther from the mainland and farther from landmasses > 5 ha when alligator presence was unlikely compared to when alligators were likely. These findings indicate that wading birds are seeking nesting locations that are less accessible to mammalian predators when alligators are not present, and that this requirement is relaxed when alligators are present. This study illustrates how a landscape-scale difference between realized and fundamental niche can result from a facilitative relationship in vertebrates.

Antipredator benefits of heterospecific colonial breeding for a predominantly solitary bird

“…Mixed-species groups are common across many taxa and may enhance anti-predatory benefits more than single-species assemblages (Stensland et al 2003;Sridhar & Guttal 2018;Boulay et al 2019;Goodale et al 2020). This may occur because species have different sensory or behaviour capabilities; for example, individuals may aggregate with more vigilant, vocal, or aggressive species that are more effective at driving predators off (Quinn & Ueta, 2008;Sharpe et al 2010;Campobello et al 2012;Goodale et al 2019;Gabel et al 2021).…”