White ibis

Avian reproduction is generally resource dependent, and resource availability can vary through time and space. Wading birds breeding activity in southern Florida wetlands is limited by availability of aquatic prey, which is largely influenced by seasonal hydrodynamics. Restoration of natural hydrologic patterns is expected to increase populations and return breeding activity in the southern Everglades, but which prey support successful breeding at coastal colonies is unknown. To address this, I examined prey use of nesting White Ibis (Eudocimus albus) at coastal colonies in Everglades National Park (ENP) in a two-year observational study. I also examined ibis diets at nesting colonies located in three regions of the Everglades to better understand regional variation in trophic support of ibis reproduction. I found that crayfish and fish were used extensively in ENP in a year with exceptional ibis breeding activity, and I provide evidence that lengthened hydroperiods in higher elevation marl prairies may enhance crayfish production and availability in the southern Everglades. I found that crayfish were the most important prey type in all regions of the Everglades when reproductive effort was highest. These results add to the growing body of evidence that crayfish are important prey for ibis reproductive success in all parts of the Everglades, and suggest that increasing water flowing into the southern Everglades may incite greater nesting at historic colony locations. With this knowledge we can forecast how wading birds, and more generally wetlands of southern Florida, will respond to a changing environment and potential restoration scenarios.

The hydrological and topographical variation of wetlands can affect the behavior,
population growth, and local densities of aquatic species, which in turn can drive the
behavior and density dynamics of gleaning predators. Prey availability, primarily
determined by prey density and water depth in wetlands, is an important limiting factor
for nesting wading bird populations, top predators in the south Florida Everglades. The
Everglades is able to support large colonies of nesting wading birds because of the
microtopographic variation in the landscape. Some types of prey concentrate in flat,
shallow sloughs or become trapped in isolated pools as they move down from higher
elevation ridges with receding water levels. Manipulations to the hydrology and
landscape of the Everglades has negatively impacted nesting wading bird populations in
the past, and may continue to be detrimental by allowing flat, shallow sloughs to be
intersected by deep canals, a potential refuge for wading bird prey. In addition, the subtle
elevation differences between the ridge and slough landscape may be an important mechanism for increasing slough crayfish (Procambarus fallax) prey availability for the
most abundant and seemingly depth-sensitive Everglades wading bird, the White Ibis
(Eudocimus albus). I implemented a 2-year experimental study in four replicated manmade
wetlands with controlled water recession rates in order to determine the effects of
proximate deep water (akin to canals) on fish prey concentrations in the sloughs, as water
levels receded similarly to a natural Everglades dry season. I also calculated average
daily wading bird densities with game cameras (Reconyx PC800 Hyperfire) using timelapse
imagery over 60 days to determine when and where wading birds responded to
changing prey concentrations. I completed an additional observational study on White
Ibis and slough crayfish prey from the first year of data (2017). Crayfish make up the
majority of the diet for nesting White Ibis, and literature has suggested crayfish are most
abundant at slough depths much deeper than previously proposed foraging depth
limitations for White Ibis. This study specifically compared recent determinations about
crayfish movement dynamics in the ridge and slough system with White Ibis foraging
behavior and depth limits. Results from the first experimental study suggest that canals
might be an attractive refuge for relatively large prey fishes (> 3 cm SL) in sloughs, but it
is uncertain if the fencing blocked all prey fish movement. The second observational
study determined White Ibis foraging activity was primarily driven by a down-gradient
crayfish flux from ridge to slough, with the majority of foraging activity occurring at
much deeper slough depths than previously suggested water depth limitations for White
Ibis. Results from both of these studies support the importance of preserving the ridgeslough
landscape of the Everglades to sustain high prey availability for wading birds.