Social and Physical Influences on Wading Bird Foraging Patch Selection

Aguiar, Amie Beth, Department of Environmental Sciences, University of Virginia
Erwin, Mike, Department of Environmental Sciences, University of Virginia
Porter, John, Department of Environmental Sciences, University of Virginia
Scanlon, Todd, Department of Environmental Sciences, University of Virginia

The aim of this study was to clarify social foraging, habitat use and choice of cohabitating Ciconiiformes on Virginia's Eastern Shore. In a 2006 study I used two approaches, a manipulative experiment and an observational study. At Chincoteague (37˚ 56'N, 75˚ 25'W), I manipulated prey density and social cues using plastic decoys to address the relative importance of social features versus prey density. I also recorded feeding durations of birds at the different treatments. The observational portion also occurred at Chincoteague at six sites along a causeway from the mainland marshes east to Assateague Island. A second area was Hog Island (37˚ 27'N, 75˚ 40'W), a barrier island about 50 km south of Chincoteague. At both areas, I observed wading bird foraging in different habitats and recorded feeding efficiency, flock size and species use, and attempted to answer the following questions: how were species distributed across habitat types, how did feeding efficiency vary among species and habitat types, and how did tide and season affect habitat use, flocking and feeding efficiency? Multi-way ANOVAs were performed to analyze feeding efficiency data and  2 analyses of goodness-of-fit and association were performed on the flock and species use data. Species' use of habitats differed significantly at both locations, with generalists being more widespread than specialists. Ponds and impoundments were selected for foraging most often by most species. Generalist species tended to have lower feeding efficiencies while species specialized for particular habitats had higher average efficiencies at those locations. Overall, generalists tended to be more widespread but have low efficiency, but specialists had high efficiencies in fewer habitat types. Tidal and seasonal effects were less than habitat and species differences, presumably because of the high caloric demands on birds ii during the breeding season. There were insufficient data to meaningfully analyze the experiment results, however the limited data suggested that all the species responded more to social cues than to prey densities. A similar experiment of increased scope and duration should be attempted, perhaps using mesocosms with more controlled prey densities. An important conservation-related finding was high late-summer use of impoundments for almost all wading birds. These habitats are probably especially attractive to recently fledged young from nearby colonies.

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MA (Master of Arts)
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