Parkes, Michael Lawrence (2007-08). Residential cattle egret colonies in Texas: geography, reproductive success and management. Master's Thesis. Thesis uri icon


  • 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.

publication date

  • August 2007