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Project Summary Sheet

U.S. Geological Survey, Greater Everglades Science Program: Place-Based Studies Initiative

Fiscal Year 2003 Project Summary Report

Project: Effects of Hydrology on Wading Bird Foraging Parameters

Project Start Date: 2000 Project End Date: 08/01/2003

Web Sites: ATLSS.ORG

Location: The Greater Everglades ecosystem

Funding Source: Critical Ecosystems Studies Initiative

Principal Investigator: Dale E. Gawlik and Fred H. Sklar, Everglades Department, South Florida Water Management District, 3301 Gun Club Road, West Palm Beach, FL 33406 (561) 682-6712, FAX 561-682-6442, dale.gawlik@sfwmd.gov

Project Personnel: Donald L. DeAngelis, Phone: 305-284-1690 e-mail: ddeangelis@umiami.ir.miami.edu

Other Supporting Organizations: USGS/BRD, NPS

Associated Projects: Component of ATLSS Program

Overview & Status: The recovery of wading bird populations has been identified as a key component of successful Everglades restoration. Proposed causes for the decline in wading bird numbers have in common the notion that current hydropatterns have altered the availability of prey. The relative importance of each component of food availability (i.e., food abundance and vulnerability to capture) is a precursor to understanding the effects of specific hydrologic regimes on wading birds. The purpose of this project is to fill data gaps by examining the response of wading birds to various components of prey availability using experimental ponds and treatments of water depth and various prey community characteristics. Prey community characteristics include fish density, fish size, and fish species. The species of wading birds examined in this study are the Wood Stork, White Ibis, Great Egret, and Great Blue Heron The objectives of the study are to: 1. Calculate prey intake rates and determine the proximate effects of water depth and fish density on wading bird foraging parameters. 2. Calculate prey intake rates and determine the proximate effects of water depth and fish size on wading bird foraging parameters. 3. Calculate prey intake rates and determine the proximate effects of water depth and fish species on wading bird foraging parameters. Capture rate (fish/min) and the mean time interval between prey captures were plotted against predicted fish density for visual and tactile feeding wading birds. After visually inspecting the data, it appeared that prey density did not influence capture rates for visually feeding birds. In other words, wading birds had similar capture rates at low and high predicted fish densities. Sample sizes were too small to draw conclusions about the tactile feeding species. Several of our experiments showed a strong numerical response to prey density by wading birds, in contrast to the apparent lack of functional response shown here. In other words, once these birds were at the ponds, capture rates were similar. One possible explanation for constant capture rates is that wading birds will leave a patch before intake rates decrease substantially. As a result, no decreasing intake rates can be detected.

Needs & Products: Study milestones and results are as follow: Development of a conceptual model of wading bird foraging behavior that allowed for quantification of time-activity budgets (1998). Prey intake rate and the associated variability was reported for 4 wading bird species at 2 prey densities and 3 water depths (January 2000). Foraging costs (as measured by the giving-up density of the prey) and associated variability was reported for 4 wading bird species at 3 water depths (January 2000). Prey intake rates and foraging costs were higher for the wood stork and white ibis than for the great egret and great blue heron (January 2000). Foraging costs for all species generally increased as a function of water depth (January 2000). Prey depletion rates in ponds increased with decreased water depths (January 2000). Analyses of prey intake rates as a function of water depth and prey size were initiated in 2001. Analyses of prey intake rate as a function of fish species were completed in 2002. The next step in this project will be integration of the results into a model of wading bird energetics.

Application to Everglades Restoration: Because this project focuses on the influence of several fish community characteristics (fish size, density, species composition) and hydrology, it demonstrates a close linkage among wading birds, lower trophic level models, and hydrologic models, and it provides a basis for integrating them.

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