The Effects of Water Depth and Emergent Vegetation on Foraging Success and Habitat Selection of Wading Birds in the Everglades

Wading bird foraging success and habitat preference can be greatly affected by prey availability, which encompasses both prey density and the vulnerability of prey to capture. Two components of prey vulnerability, water depth and emergent vegetation, were manipulated within 10 m × 10 m enclosures to determine the relative effects on foraging habitat preference for eight species of wading birds and foraging success for a subset of four species that strike their prey. All species showed a strong preference for shallow water, and within this water depth showed a preference for the sparse vegetation density treatment. The preference for foraging habitat with a sparse or intermediate vegetation density has been documented in other studies, and may represent a tradeoff between selecting more heavily vegetated areas, which have a higher prey density, and more open areas, where prey are more vulnerable to capture. Almost all foraging occurred in the shallow water treatment, suggesting that preferred water depths constituted high quality habitat for wading birds. The weaker selection for sparse vegetation density and lack of an effect of vegetation density on capture rate and capture efficiency (p>0.05 for all tests, except Snowy Egret (Egretta thula) capture efficiency) suggested that emergent vegetation is of secondary importance to water depth as determinants of wading bird habitat quality.