Reproductive Success of Colonial Tree-nesting Waterbirds in Prairie Pothole Wetlands and Rivers throughout Northeastern South Dakota

Abstract

The northern Great Plains of North America provides critical breeding habitat for many colonial tree-nesting waterbirds, but reproductive success and population parameters for these species are largely unknown within the Prairie Pothole Region, specifically in South Dakota. The objective of this study was to evaluate reproductive success of colonial tree-nesting waterbirds on selected wetlands and rivers in northeast South Dakota. During the 2008 and 2009 breeding seasons, nesting and fledging success of Black-crowned Night-Heron (Nycticorax nycticorax), Great Blue Heron (Ardea herodias), Cattle Egret (Bubulcus ibis), Great Egret (A. alba), Snowy Egret (Egretta thula), and Double-crested Cormorant (Phalacrocorax auritus) were estimated in 39 individual colonies. A total of 2551 individual nests were monitored from 15 Apr. - 15 Aug. in 2008 and 2009. Overall apparent nest and fledge success (respectively) were: Black-crowned Night-Heron (52.1%, 47.9%), Great Blue Heron (58.2%, 35.9%), Cattle Egret (73.1%, 69.2%), Great Egret (61.5%, 50.7%), Snowy Egret (83.6%, 81.7%), and Double-crested Cormorant (70.4%, 54.2%). Nest abandonment accounted for an average of 47.6% of nest failures for all species combined. Nest structure failure and young dying within nests accounted for most failures to fledge. Nesting success increased with the area of wetland habitat in the landscape for all species analyzed. Lower reproductive success of Black-crowned Night-Heron and Great Blue Heron, compared to other findings across the U.S. and Canada, suggests that these breeding populations in northeast South Dakota may be declining. Cattle Egret, Great Egret, Snowy Egret, and Double-crested Cormorant reproductive success is relatively high in northeast South Dakota compared to other North American populations. Preserving and restoring wetland habitat surrounding waterbird colonies will provide successful nesting habitat as well as foraging areas and opportunities for new colony site locations.