Beerens, James M.

In south Florida, the Greater Everglades ecosystem supports sixteen species of
wading birds. Wading birds serve as important indicator species because they are highly
mobile, demonstrate flexible habitat selection, and respond quickly to changes in habitat
quality. Models that establish habitat relationships from distribution patterns of wading
birds can be used to predict changes in habitat quality that may result from restoration
and climate change. I developed spatio-temporal species distribution models for the
Great Egret, White Ibis, and Wood Stork over a decadal gradient of environmental
conditions to identify factors that link habitat availability to habitat use (i.e., habitat
selection), habitat use to species abundance, and species abundance (over multiple scales)
to nesting effort and success. Hydrological variables (depth, recession rate, days since
drydown, reversal, and hydroperiod) over multiple temporal scales and with existing
links to wading bird responses were used as proxies for landscape processes that influence prey availability (i.e., resources). In temporal foraging conditions (TFC)
models, species demonstrated conditional preferences for resources based on resource
levels at differing temporal scales. Wading bird abundance was highest when prey
production from optimal periods of wetland inundation was concentrated in shallow
depths. Similar responses were observed in spatial foraging conditions (SFC) models
predicting spatial occurrence over time, accounting for spatial autocorrelation. The TFC
index represents conditions within suitable depths that change daily and reflects patch
quality, whereas the SFC index spatially represents suitability of all cells and reflects
daily landscape patch abundance. I linked these indices to responses at the nest initiation
and nest provisioning breeding phases from 1993-2013. The timing of increases and
overall magnitude of resource pulses predicted by the TFC in March and April were
strongly linked to breeding responses by all species. Great Egret nesting effort and
success were higher with increases in conspecific attraction (i.e., clustering). Wood Stork
nesting effort was closely related to timing of concurrently high levels of patch quality
(regional scale) and abundance (400-m scale), indicating the importance of a multi-scaled
approach. The models helped identify positive and negative changes to multi-annual
resource pulses from hydrological restoration and climate change scenarios, respectively.

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.