BROOD PARASITISM IN A NORTH AMERICAN POPULATION OF WHITE-FACED IBIS

In 2007 while monitoring reproductive success among various overwater nesting birds at J. Clark Salyer National Wildlife Refuge in North Dakota, I observed parasitism of a white-faced ibis nest by a cattle egret. I located a nest on 23 May 2007 that contained four white-faced ibis eggs and one cattle egret egg. The nest was located in the middle of a small colony of nesting white-faced ibis (approximately 35 pairs) and black-crowned night herons (approximately 30 pairs). On 3 June 2007 all of the eggs were still present in the nest, but two of the white-faced ibis eggs began hatching on 5 June 2007. I returned to the nest on 10 June 2007 and observed three white-faced ibis chicks and one cattle egret chick in the nest. The fourth ibis egg was in the water beside the nest. I estimated two of the ibis chicks to be 4-5 days old and the other ibis chick and the egret chick to be 2-3 days old based on the plumage and size of other white-faced ibis and cattle egret chicks of known age that I observed in the colony. The nest was still active (with all four of the chicks present) on 15 June 2007. I did not monitor the nest after 15 June 2007 because nests with 10-day or older ibis chicks are no longer visited to prevent flushing chicks away from the nest site. All nest monitoring was conducted in accordance with North Dakota State University Institutional Animal Care and Use Committee (#A0759)