Wetlands and the animals they support have experienced a dramatic decline as human pressures have increased. Over 53% of wetlands in the U.S. were lost between the 1780s to the 1980s (Mitsch and Gosselink 2007). Many other wetlands remain intact but their functionality has been reduced through eutrophication and drainage (Mitsch and Gosselink 2007). One large wetland system that historically supported large numbers of nesting wading birds was Lake Okeechobee (hereafter the Lake) and surrounding marshes (David 1994a). Beginning in 1884, rivers flowing into the Lake were channelized and the flow was diverted to the east and west into the St Lucie and Caloosahatchee River, respectively. Lake water, regulated since 1931, now serves as the primary water supply for South Florida's expanding human population. Altered flows and water management infrastructure have led to increased nutrient transport, eutrophication, and a reduction in the spatial extent and heterogeneity of the associated wetlands (Dovell 1956; Havens and Gawlik 2005). High water levels reduced water clarity, triggering a loss of submerged aquatic vegetation, a reduction in the production of aquatic fauna, drowned willow heads, and a drop in numbers of nesting wading birds (David 1994b; Havens and Gawlik 2005). The collapse of the Lake's food web also compromised the economic health of the surrounding area because the Lake supported high levels of ecotourism and recreational fishing (Steinman et al. 2002; Johnson et al. 2007). Concern for the ecological integrity of the Lake ecosystem led to subsequent modifications of water management regimes to better mimic natural hydrologic fluctuations (Havens and Gawlik 2005).
Although the quality of foraging patches is important, their spatial and temporal distribution, as well as the connectivity of patches, is critical for successful wading bird nesting (Strong et al. 1997). While flight distance does not constrain birds, distance determines whether a foraging location is energetically efficient. During the breeding season, a wading bird will be constrained by its nest, which it must return to every day. Nests of colonial breeders are typically located within inundated willow heads and spoil island nesting sites, locations where mammalian predation on nests is likely to be reduced (Frederick and Collopy 1989; David 1994a; Smith and Collopy 1995). During rearing, more energy is invested and the presence of quality foraging locations within range becomes increasingly important as locations must have a prey concentration high enough to compensate for the energetic cost of flying that distance (Bancroft et al. 1990; Smith 1995). By comparing habitat suitability within the adults’ foraging range to nest success, we can attempt to link reproductive success with surrounding environmental factors (Hall et al. 1997).
Link the nesting response of three species of wading birds to habitat conditions on the Lake. Specifically, I will estimate nesting effort and success and relate it to the quality and distribution of foraging habitat predicted by the HSM.