Cooperative Fish and Wildlife Research Units Program: Vermont
Education, Research and Technical Assistance for Managing Our Natural Resources

We studied foraging distribution, activity budgets, fi sh consumption, and energetics of double-crested cormorants (Phalacrocorax auritus) at two breeding colonies on Lake Champlain. Our objective was to determine if fi sh consumption and distribution of predation changed with movements of cormorants associated with efforts to reduce numbers of cormorants on one of the colonies. Wildlife managers reduced populations of cormorants on Young Island, Vermont by oiling their eggs, which resulted in dispersal of breeding cormorants 35 km south to Four Brothers Islands, New York. We found that as cormorants shifted from Young Island to the colony on Four Brothers Islands, energy demands, foraging distribution, and total fi sh consumption increased. Birds on Four Brothers Islands foraged a greater distance from the colony compared to birds on Young Island. Additionally, consumption of yellow perch (Perca flavescens) shifted to rainbow smelt (Osmerus mordax) when more birds bred on Four Brothers Islands. The dispersal of cormorants from Young Island to Four Brothers Islands reduced predation on yellow perch but increased overall fish consumption. Our estimates of fish consumption ranged from 322,000–425,000 kg of fi sh per year at Young Island to 899,000–1,086,000 kg of fish per year at Four Brothers Islands. Results from this study demonstrate secondary impacts of management on Young Island to unmanaged areas.