U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Date of this Version



Published in National Sunflower Association Research Forum Papers 2006.


Many of the suggested management techniques directed at reducing blackbird breeding populations fail to incorporate the underlying mechanisms regulating populations. Theoretically, removal of individuals from the breeding population should lower the breeding densities and presumably reduce recruitment. However, compensatory responses might occur with decreased breeding densities, but no empirical data are available to test this hypothesis. Much of the underlying compensatory theory is based on differential allocation of resources to reproduction vs. self maintenance at different breeding densities, mainly in the form of depensatory effects of resource limitation on growth and survival. However, as the breeding density in an area changes, social interactions among individuals also change (Whittingham and Schwabl 2002; Pilz and Smith 2004). Recent research has shown maternally derived steroid hormones present in eggs offer a potential compensatory mechanism by which adult social interactions affect offspring growth and survival (Schwabl 1996a; Schwabl 1996b). Gaining insight into the underlying mechanisms regulating red-winged blackbird populations will allow for more effective and efficient management techniques. This study focuses on the effects of density and social interactions on Red-winged Blackbird reproduction, and the associated underlying mechanisms.