Residential cattle egret colonies in Texas: geography, reproductive success and management

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Title: Residential cattle egret colonies in Texas: geography, reproductive success and management
Author: Parkes, Michael Lawrence
Abstract: A phenomenon of large , upland breeding colonies of cattle egrets in residential areas of Central Texas has been observed since the early 1960s . These large concentrations of breeding birds can be a nuisance to nearby residents and their management has been difficult . To help understand why cattle egrets choose upland , residential breeding sites , and predict where these might occur , the geographic extent of the phenomenon was bounded within Texas , a habitat suitability model constructed , and reproductive success compared by breeding habitat type to evaluate if residential nesting confers an adaptive advantage . . Records of upland cattle egret colonies were found only in Central Texas , not other parts of the state . The habitat suitability model was constructed using total edge of three land use classes : water , forest , and developed classes . The model classified 78 .6 % of upland colonies in very high or high suitability classes and 7 .1 % of colonies in low or very low suitability classes . This distribution was significantly different than expected considering the overall ratio of suitability scores in the entire raster model (p = 0 .036 ) . Nineteen active colonies were found in or bordering the Post Oak Savannah and Blackland Prairie ecoregions . Colonies were in residential , urban , island , and flooded tree and shrub habitat . Nests were found in 12 different tree and shrub species . Residential colonies had more breeding pairs , greater nest survival , and were less productive than non -residential colonies on average , but these differences were not statistically significant . Colonies where nest substrate was removed were not reused and no breeding was initiated nearby the next year . Propane cannons discouraged reuse of colony after prolonged application . Herons and egrets likely use residential sites when wetland habitats are limited . Their overall breeding distribution reflects state wide rainfall and wetland availability patterns with upland nesting in Central Texas , wetland nesting in eastern and coastal regions , and little large scale nesting in western Texas . Egrets and herons may use edges of development as breeding sites to limit predation by ground predators when flooded tree and shrub or island habitats are absent , but this hypothesis needs more testing .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1639
Date: 2009-05-15


Residential cattle egret colonies in Texas: geography, reproductive success and management. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1639 .

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