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Project Summary Sheet

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

Fiscal Year 2002 Project Summary Sheet

Project: Effects of Hydrology on Wading Bird Foraging Parameters

Web Sites: ATLSS.ORG

Location (Subregions & Counties): The total system

Funding (Source): Critical Ecosystems Study Initiative (CESI), South Florida Water Management District

Principal Investigator(s): 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,

Project Personnel: Donald L. DeAngelis, Phone: 305-284-1690, e-mail:

Supporting Organizations: USGS/BRD, NPS, SFWMD

Associated / Linked 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 Across Trophic Level System Simulation (ATLSS) program integrates such information and provides predictive power for future management decisions. Currently, the biggest information gap limiting the wading bird component of ATLSS is foraging success as a function of prey availability and water depths. The purpose of this project is to examine 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 those in the ATLSS wading bird model: 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.

Needs & Products: Information from this project directly supports the development of the ATLSS Wading Bird Model. Uses and information needs for the ATLSS wading bird model are addressed elsewhere. The most prominent missing information for the ATLSS Wading Bird Model is foraging success in relation to prey availability. Foraging parameters from this study, with species-specific responses to prey availability at levels found within the Everglades, will be used to replace values derived from the literature or generalized from studies of other species and other levels of prey availability. Study milestones and results are as follows: 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. A preliminary step in that analysis was to assess the potential for sampling bias with throw traps as a function of fish size. A rigorous analysis of the data showed that although prey density estimates from throw traps varied considerably among experimental cells, there was no bias in fish density estimates associated with fish size. Prey intake rate and associated variability as a function of water depth and fish size are currently being calculated for the 4 wading bird species. In June 2002, analyses of prey intake rate as a function of fish species will be initiated.

Application to Everglades Restoration: This project will provide a rational, scientific basis for ranking the hydrologic scenarios as input to the Everglades restoration planning process, and through this to aid development of appropriate monitoring and adaptive management schemes. 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.

Study Milestones
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
Familiarity         x x x x      
Design         x            
Field Work         NA            
Data Analysis         x x x o o    
Initial Reporting         x x x o o    
Quality Assurance         x x x x o    
Results Published                 o    
Synthesis                 o    
Note: "x" indicates task completed during quarter, and "o" indicates task planned, but not completed

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