Studies show that prey availability within a habitat is important in determining foraging site selection by wading birds (Gawlik 2002, Safran et. al. 2000, Frederick and Spalding 1994). Prey availability, used interchangeably with food availability, is the major factor limiting reproductive success in wading birds (Powell and Powell 1986). However, factors affecting prey availability are poorly understood (Frederick and Spalding 1994).
The idea that prey availability limits wading bird population sizes is termed the “prey availability hypothesis” (Gawlik 2002). This hypothesis draws from studies showing that reproduction is driven by the availability of food, which is in turn driven by hydrologic conditions (Gawlik 2002). Prey availability is a combination of prey density and the vulnerability of that prey to capture. Vulnerability to capture is affected by characteristics of the predator, prey, and environment. The factors affecting wading bird prey availability and foraging success can be explored in a conceptual model (Figure 1). In this experiment, vegetation, prey populations, and water depth are all controlled variables which in the Everglades are controlled mainly through hydrology and nutrients. These variables, in combination with additional characteristics of the wading birds, prey, and the environment, contribute to the formation of high-quality patches. Through analysis of wading bird response, specific levels of the treatment variables will be identified that contribute to high-quality patches.
In this study, 10 x 10 m enclosures will be established in the experimental macrocosms at the Loxahatchee Impoundment Landscape Assessment site (LILA), part of the ARM Loxahatchee National Wildlife Refuge. Enclosures will be subjected to two water depths and three vegetation density treatments in order to determine how these habitat characteristics affect wading bird foraging. Mosquitofish (Gambusia holbrooki) will be stocked in the enclosures at a density of 20 fish/m2. This density will be maintained throughout the experiment by marking a subset of fish with Visible Implant Elastomer (Northwest Marine Technology) and determining density through mark-recapture.
Objectives
Quantify the effects of submerged vegetation density and water depth on wading bird prey availability and foraging success.
Quantify the effects of emergent vegetation density and water depth on wading bird prey availability and foraging success.
