2005 WISCONSIN DOUBLE-CRESTED CORMORANT BREEDING SURVEY

US Department of Agriculture

The interior population of the Double-crested cormorant (Phalacrocorax auritus) has increased dramatically over the last 30 years. In Wisconsin, cormorants were listed as state endangered in 1972; presumably due to the effects of DDT, habitat deterioration, and human disturbance. Following protection and management efforts, the cormorant breeding population increased dramatically and the bird was delisted from “threatened” status in 1986. Between 1973 and 1997, the State’s breeding population increased 25% annually from 66 nests at 3 colonies to 10,546 nests at 23 colonies (Matteson et al. 1999). The population increase and associated impacts are not exclusive to Wisconsin. Breeding populations in the Great Lakes region have increased from 200 nesting pairs in 1968 to approximately 115,000 nesting pairs in 2000 (Ludwig 1984, D. V. C. Weseloh, unpublished data). Concurrent with the population increase, conflicts and concerns over economic impacts associated with cormorant depredation at aquaculture facilities (mainly catfish farms) in the south have increased. The nation-wide population increase prompted a multi-agency initiative to establish a cormorant management plan. In Wisconsin, the U.S. Fish and Wildlife Service (FWS), USDA – Wildlife Services (WS), Wisconsin Dept. of Natural Resources (DNR), National Park Service (NPS), and private individuals coordinated efforts to count nests at active breeding colonies. The last state-wide population survey was conducted in 1997 (Matteson et al. 1999) and all active colonies were revisited in 2005.Objectives of the breeding survey were to update the state-wide number of breeding pairs, identify new breeding colonies, and verify the status of historically active colonies.