Reproductive Characteristics of Double-crested Cormorants (Phalacrocorax auritus) in the Eastern United States: Demographic Information for an Intensely Managed Species

Double-crested Cormorants (Phalacrocorax auritus) are intensely managed through culling in North America to reduce presumed damage to commercial and natural resources. To evaluate this management, there is a critical need to understand the reproductive biology of Double-crested Cormorants. Gonadal development, reproductive potential and breeding status were determined by necropsy for 1,781 DOuble-crested Cormorants salvaged each month of the year from control programs in their wintering and breeding ranges in seven States in the USA. Gonadal development of males peaked earlier in the year than females. Mean and maximum reproductive potential was five and 13 ovum, respectively. The average proportion of non-breeding female Double-crested Cormorants culled from breeding colonies was 14.9% (n = 202) and from foraging flocks on the breeding grounds was 22.1% (n = 358). This demographic information should be considered when evaluating and modeling effects of Double-crested Cormorant management in North America.