Great lakes double-crested cormorant management affects co-nester colony growth

TitleGreat lakes double-crested cormorant management affects co-nester colony growth
Publication TypeJournal Article
Year of Publication2018
AuthorsWyman KE, Wires LR, Cuthbert FJ
JournalThe Journal of Wildlife Management
Pagination93 - 102
Date PublishedJan-01-2018
KeywordsArdea herodias, culling, double-crested cormorant, Larus argentatus, Larus delawarensis, North American Great Lakes, Nycticorax nycticorax, Phalacrocorax auritus, population growth

The population of double-crested cormorants (Phalacorocorax auritus; cormorants) in the North
American Great Lakes has increased substantially since the 1970s, sparking economic, social, and biological
concerns that have led to widespread management of the species within United States waters. Previous
studies have quantified behavioral impacts of cormorants on other waterbird species that share breeding
colony sites with cormorants. However, no study has yet examined how these impacts might scale to entire
colonies, nor have potential effects of cormorant management on co-nesters been examined. Our objective
was to estimate effects of cormorant abundance and management on colony growth indices of 4 species that
commonly co-nest with cormorants in the North American Great Lakes; 3 of these species are conservation
or stewardship priorities for the region. We estimated colony growth using the Great Lakes Colonial
Waterbird Survey and comparable Canadian surveys, conducted between 1976 and 2010. We then applied
linear mixed models to determine association of co-nester colony growth indices with cormorant abundance
and management presence and intensity while controlling for other factors that likely influenced growth
rates. According to the fitted models, black-crowned night-heron (Nycticorax nycticorax) colony growth was
negatively related to cormorant abundance and management, whereas great blue herons (Ardea herodias) had
little response to cormorant abundance, and herring gulls (Larus argentatus) and ring-billed gulls (Larus
delawarensis) responded positively to cormorant abundance and management. These results suggest that
cormorant management may not be as neutral to co-nesters as is often assumed. Responsible management
plans for cormorants should take into account the likely effects on co-nesters present so that conservation and
management goals for co-nesters can also be met. 2017 The Wildlife Society.

Short TitleJour. Wild. Mgmt.
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