Differences in Reproductive Ecology and Behavior of the Polymorphic Reddish Egret (Egretta rufescens)




Holderby, Zachary P.

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Assessing and maintaining genetic diversity is a concern for the conservation and management of a species, since variations within a species dictate its evolutionary potential. The Reddish Egret Egretta rufescens is a relatively rare heron species that exhibits white-dark plumage polymorphism. Different regions within the Reddish Egret's geographic range have different ratios of dark and white morphs. This may imply different microevolutionary processes affecting the frequency of the two morphs in different habitats and populations. I investigated how this phenotypic difference influences the behavior and reproductive ecology of the white and dark morph Reddish Egrets in the upper Laguna Madre of Texas. On dredge spoil islands in the Laguna Madre, Reddish Egret nesting pairs were observed during forty minute focals as they courted, built nests, and raised young. I collected time-spent behavioral data, reproductive ecology information, and characterized vegetation of nests and the surrounding area. Regurgitant from chicks was collected opportunistically to determine differences in diversity and abundance of prey fed to young. Nest vigilance and nest initiation did not differ between morphs or nest sites, but nest attendance varied between morphs depending on nest site. Feeding time of chicks differed between morphs and is potentially related to foraging efficiency and time of day. Nest cover did not vary between morphs within sites, but varied significantly between sites and between random points and nests within sites. This indicates strong selection of nest sites within colonies. The information obtained provides valuable insights into the ecological diversity of polymorphic species, and information on nest site selection and prey diversity that could be considered for the conservation of this rare waterbird.



reproduction, egretta, herons, polymorphism, zoology


Holderby, Z. P. (2009). Differences in reproductive ecology and behavior of the polymorphic reddish egret (Egretta rufescens) (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.


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