Interactions Between Double-crested Cormorants and Herring Gulls at a Shared Breeding Site

Somers, Christopher M.; Lozer, Marie N.; Quinn, James S.

doi:10.1675/1524-4695(2007)30[241:ibdcah]2.0.co;2

Cited by 23 publications

(21 citation statements)

References 18 publications

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“…Herring gulls and ring‐billed gulls showed a strongly positive response to cormorant abundance, contrary to an earlier finding by Somers et al () of reduced reproductive success in herring gulls nesting with cormorants. The herring gull work conducted by Somers et al (, ) may have been confounded by human disturbance, but according to our fitted models, herring gulls in particular have an almost exclusively positive response to presence of cormorant management, a situation in which human disturbance is almost unavoidable. Indeed, there are indications that cormorant management is associated with increased herring gull nest success (B. S. Dorr, U.S. Department of Agriculture [USDA] Wildlife Services, personal communication).…”

Section: Discussioncontrasting

confidence: 96%

Section: Gull Response To Cormorant Abundance and Managementcontrasting

confidence: 99%

“…Herring gulls and ring-billed gulls showed a strongly positive response to cormorant abundance, contrary to an earlier finding by Somers et al (2007) of reduced reproductive success in herring gulls nesting with cormorants. The herring gull work conducted by Somers et al (2007Somers et al ( , 2011 (taken in 1989-1991, 1997-1999, and 2007-2010) from all sites occupied by the conesting species at least once within the 4 survey periods. Several researchers have reported that gulls can take advantage of human disturbance of cormorant colonies to depredate cormorant nests (Kury and Gochfeld 1975, Ellison and Cleary 1978, DesGranges and Reed 1981, and this food resource may explain the boost in colony growth index.…”

Section: Gull Response To Cormorant Abundance and Managementcontrasting

confidence: 99%

“…Declines in wading bird abundance have been observed at some shared breeding sites, but authors of these studies were unable to or did not conclusively link declines directly or indirectly to activities of cormorants (Skagen et al , Cuthbert et al ). On the other hand, cormorant presence has been observed to change the frequency with which co‐nesters engage in agonistic interactions, particularly in ground‐nesting colonies (Somers et al , Somers et al , Wyman and Cuthbert ). In one case, cormorants were associated with reduced herring gull ( Larus argentatus ) breeding success, although human disturbance was a confounding factor in the study (Somers et al ).…”

mentioning

confidence: 99%

“…On the other hand, cormorant presence has been observed to change the frequency with which co‐nesters engage in agonistic interactions, particularly in ground‐nesting colonies (Somers et al , Somers et al , Wyman and Cuthbert ). In one case, cormorants were associated with reduced herring gull ( Larus argentatus ) breeding success, although human disturbance was a confounding factor in the study (Somers et al ). Co‐nester responses to cormorant management have received little direct research attention.…”

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confidence: 99%

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

2017

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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. Ó 2017 The Wildlife Society.

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Section: Discussioncontrasting

confidence: 96%

Section: Gull Response To Cormorant Abundance and Managementcontrasting

confidence: 99%

Section: Gull Response To Cormorant Abundance and Managementcontrasting

confidence: 99%

mentioning

confidence: 99%

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

2017

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Aquaculture depredation by double‐crested cormorants breeding in Eastern North America

et al. 2015

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The double‐crested cormorant (Phalacrocorax auritus) has undergone population expansion throughout much of its historical range since the 1970s, resulting in increased pressure on foraging habitats including real and perceived competition with commercial and sport fisheries and impacts on the aquaculture industry. The specific objectives of this study were to determine the stable isotope ratios of birds wintering at aquaculture facilities and natural freshwater and marine habitats, and to determine what percent of birds at distinct breeding colonies wintered in each of these habitats. We exploited natural variation in isotopic ratios of carbon, nitrogen, and sulfur (from feathers) to determine the winter habitat use (i.e., aquaculture, natural freshwater, or marine) of birds collected on their summer breeding grounds in the eastern United States (from Minnesota to Vermont). The distribution of winter habitat use varied significantly across breeding colonies and between male and female cormorants. More specifically, use of aquaculture winter habitat was most prevalent in birds breeding in Lake Huron and Lake Erie. Overall, aquaculture habitats were used more by males, and marine habitats were used more by females. The stable isotope approach used in this study provided dietary confirmation of previously observed migratory patterns in the double‐crested cormorant. Because aquaculture was primarily used by males, and these males migrated to a broad range of breeding colonies, we suggest that targeting breeding birds to reduce aquaculture depredation is a less efficient strategy than managing birds at depredation sites on the wintering grounds. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

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