Habitat selection

Understanding the foraging and nesting ecology of Wood Storks will play an
important role in Everglades restoration because this species has specific resource
requirements during the breeding season which ultimately affect nest success. I
conducted a foraging habitat use and selection study, which indicated that Wood Storks
from coastal colonies, Paurotis Pond and Rodgers River Bay, require a narrow range of
water depths in the mangrove-saltwater marsh ecotone near their colonies as well in the
freshwater marsh habitats of the inland Everglades. Wood Storks nesting at the inland
colony, Tamiarni West, relied heavily upon nearby freshwater marsh habitat and selected
foraging sites associated with shrub swamp habitat as well as optimal water depths. The
observational nesting ecology study of Wood Storks showed marked differences in
parental nest attendance and food delivery rates between the two years of study, 2005 and
2006, which had different hydrological patterns.

The first of five chapters describe the study area and study species, including a short description
about the impetus for this research. The second chapter describes a unique hydrologic model for application
in tidal ecosystems. The second chapter represents new information on the effects of various abiotic and
biotic factors on foraging wading birds in this highly dynamic environment. The third chapter identifies
important factors affecting the abundance of foraging wading birds in intertidal environments. The fourth
chapter presents a study of the foraging habitat preferences of two wading bird species in intertidal
environments. The fifth chapter describes a conceptual model of wading bird foraging ecology and a
predictive model of foraging habitat in intertidal zones. The conceptual model captures the major drivers
and linkages between the abiotic and biotic variables thought to affect wading bird foraging abundance in
intertidal habitats. The conceptual model also identifies major knowledge gaps in our understanding of
foraging ecology of wading birds in coastal intertidal areas. The predictive model of foraging habitat is
meant to be used by resource managers, but its framework may be useful for ecological studies in general.
The final and sixth chapter provides a summary of all the major findings. Each chapter has been written so
as to be independent of the other chapters. As such, a full background, along with a discussion of the
relevance of the chapter's findings is provided for each chapter.

Understanding where and why organisms are distributed in the environment are central themes in ecology. Animals live in environments in which they are subject to competing demands, such as the need to forage, to find mates, to reproduce, and to avoid predation. Optimal habitats for these various activities are usually distributed heterogeneously in the landscape and may vary both spatially and temporally, causing animals to adjust their locations in space and time to balance these conflicting demands. In this dissertation, I outline three studies of Procambarus fallax in the ridge-slough landscape of Water conservation Area 3A (WCS-3A). The first section outlines an observational sampling study of crayfish population distribution in a four hectare plot, where I statistically model the density distribution at two spatial scales. ... Secondly, I use radio telemetry to study individual adult crayfish movements at two study sites and evaluate habitat selection using Resource Selection Functions. In the third section, I test the habitat selection theory, ideal free distribution, by assessing performance measures (growth and mortality) of crayfish in the two major vegetation types in a late wet season (November 2007) and early wet season (August 2009).

Trade-offs in traits conferring success in permanent and ephemeral habitats are often at odds with few species being able to persist in both types of environments. I examined the effect of sunfish predators on two species of south Florida crayfish to establish the mechanism that limits one species, Procambarus alleni, to short-hydroperiod environments. The crayfish assemblage response to a gradient of sunfish predators and the effect of predation on P. fallax alone was examined. I also examined the effects of sunfish on crayfish growth and quantified activity levels and risky behaviors of both crayfish species. P. alleni dominated at low sunfish densities but dominance shifted with increasing sunfish density. P. alleni was more active and likely to initiate risky behaviors, suggesting that sunfish predators remove the more active P. alleni, reducing their numbers disproportionally to those of P. fallax and allowing P. fallax to dominate crayfish assemblages in long-hydroperiod wetlands.

Successful foraging by avian predators is influenced largely by prey availability. In a large-scale experiment at the Loxahatchee Impoundment Landscape Assessment project within the Arthur R. Marshall Loxahatchee National Wildlife Refuge, I manipulated two components of prey availability, water depth and vegetation density (submerged aquatic vegetation and emergent vegetation), and quantified the response by wading birds in terms of foraging habitat selection and foraging success. Manly's standardized selection index showed that birds preferred shallow water and intermediate vegetation densities. However, the treatments had little effect on either individual capture rate or efficiency. This was a consistent pattern seen across multiple experiments. Birds selected for certain habitat features but accrued little benefit in terms of foraging success. I hypothesize that birds selected sites with shallow water and intermediate vegetation densities because they anticipated higher prey densities, but they did not experience it here because I controlled for prey density.

Seasonal variation in food availability is one of the primary limitations to avian populations, particularly during the breeding season. However, the behavioral responses between species may differ based on foraging strategies. I examined the influence of food availability on landscape-level habitat selection, patch-level habitat selection, and movements of two wading bird species with divergent foraging strategies, the Great Egret and White Ibis. On a landscape scale, there appeared to be a relationship among resource availability, the temporal scale of the independent variable, and whether the response was similar or different between species. At the patch level, results demonstrated a relationship between resource availability and the spatial scale of the independent variables selected by birds. Species movements were consistent with the differing strategies. This study is the first to make the link between landscape hydrology patterns, prey availability, and responses in wading bird habitat selection at multiple spatial scales.

A challenge to ensure the health of wading bird populations is to have a better understanding of the altered habitats that we must now consider part of their natural history. Throughout their range endangered Wood Storks (Mycteria americana) have been reported to forage in ditches, a disparate category of linear man-made waterways. In a 52-kmP 2 P study area on the east coast of central Florida, the characteristics of hydrologically diverse ditches were quantified, and their use by Wood Storks documented during their non-breeding season. Logistic regression analyses were carried out using the ditch characteristics as independent variables and Wood Stork presence/absence as the dependent variable. This study confirms the use of these marginal wetlands, and identifies the significance of emergent vegetation on the foraging habitat selection of Wood Storks in the dry season.