Colony fidelity and dispersal can have important consequences on the population dynamics of colonial-nesting birds. We studied survival and inter-colony movements of Double-crested Cormorants (Phalacrocorax auritus; cormorants) nesting at Spider and Pilot islands, located 9 km apart in western Lake Michigan, during 2008-2014. We used live resighting and dead recovery data from both colonies, plus dead recoveries from throughout North America, in a multistate live and dead encounter model to estimate annual survival, inter-colony movements, plus temporary and permanent emigration to unmonitored sites. Annual survival averaged 0.37 (annual process variation, σ=0.07) for hatch-year, 0.78 (σ=0.08) for second-year, and 0.89 (σ=0.04) for after-second year birds. The best approximating model recognized only 2 age classes for transition probabilities, indicating little difference in fidelity and movement probabilities after the natal year. Annual fidelity to Spider and Pilot islands averaged 0.53 (σ=0.17) and 0.48 (σ=0.24) for second-year and 0.55 (σ=0.23) and 0.62 (σ=0.16) for after-second year cormorants, respectively, indicating substantial emigration for both age classes. For birds that dispersed, emigration was approximately equally divided among neighboring colonies, temporary emigration sites from which surviving birds subsequently returned, or permanent emigration sites from which birds never returned (but were still encountered through dead recoveries). Our results indicate that Double-crested Cormorants in the Great Lakes have tremendous potential to disperse, which may help to explain their rapid recolonization following historically low populations in the early 1970s.
Bibliographical noteFunding Information:
We acknowledge the help of USDA Wildlife Services, West Virginia University, and USFWS staff with data collection. Brett Sandercock, Bret Collier, and an anonymous reviewer provided helpful reviews on earlier drafts of the manuscript. Funding statement: Funding was provided by the U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services and the U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, National Wildlife Research Center, Cooperative Agreements #14-7428-1030-CA, #15-7428-1030-CA. Ethics statement: Use of avian subjects was approved by the USDA, WS, National Wildlife Research Center’s Institutional Animal Care and Use Committee (QA-1980). Author contributions: B.S.D., K.C.H.-D., and K.S. conceived the idea, design, or experiment (supervised research, formulated question or hypothesis). K.S., K.C.H.-D., B.S.D., and C.R.A. performed the experiments (collected data, conducted the research). C.R.A., T.W.A., K.C.H.-D., and B.S.D. wrote the paper. K.S., K.C.H.-D., B.S.D., T.W.A., and J.S.I. developed or designed methods. C.R.A. and T.W.A. analyzed the data. K.S. and B.S.D. contributed substantial materials, resources, or funding. Data availability: All data for bird banding and band observation are archived with U.S. Department of Agriculture, Wildlife Services, National Wildlife Research Center under QA-1980 and are available on request. https://www.aphis. usda.gov/aphis/ourfocus/wildlifedamage/programs/nwrc/ sa_information_services/ct_archives
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- Lake Michigan
- Phalacrocorax auritus
- colonial waterbird
- multistate model
- temporary emigration