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

Katherine E. Wyman, Linda R. Wires, Francesca J. Cuthbert

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish (US)
Pages (from-to)93-102
Number of pages10
JournalJournal of Wildlife Management
Volume82
Issue number1
DOIs
StatePublished - Jan 2018

Bibliographical note

Funding Information:
The authors thank the many cooperators who participated in the Great Lakes Colonial Waterbird Survey. Special thanks go to W. C. Scharf, G. W. Shugart, J. E. McKearnan, and D. DeRuiter. Thank you to D. V. C. Weseloh and D. J. Moore, who organized Canadian surveys and shared data with us. T. W. Arnold and B. S. Dorr advised on model design and S. J. Lewis assisted in data procurement. The USFWS funded the 4 Great Lakes Colonial Waterbird Surveys. K. E. Wyman was additionally supported by a Doctoral Dissertation Fellowship from the University of Minnesota. F. J. Cuthbert’s contribution to the work was supported by the USDA National Institute of Food and Agriculture, Hatch project 1007020.

Keywords

  • Ardea herodias
  • Larus argentatus
  • Larus delawarensis
  • North American Great Lakes
  • Nycticorax nycticorax
  • Phalacrocorax auritus
  • culling
  • double-crested cormorant
  • population growth

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