Demographics of piscivorous colonial waterbirds and management implications for ESA-listed salmonids on the Columbia Plateau

Northwest Science
By: , and 

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Abstract

We investigated colony size, productivity, and limiting factors for five piscivorous waterbird species nesting at 18 locations on the Columbia Plateau (Washington) during 2004–2010 with emphasis on species with a history of salmonid (Oncorhynchus spp.) depredation. Numbers of nesting Caspian terns (Hydroprogne caspia) and double-crested cormorants (Phalacrocorax auritus) were stable at about 700–1,000 breeding pairs at five colonies and about 1,200–1,500 breeding pairs at four colonies, respectively. Numbers of American white pelicans (Pelecanus erythrorhynchos) increased at Badger Island, the sole breeding colony for the species on the Columbia Plateau, from about 900 individuals in 2007 to over 2,000 individuals in 2010. Overall numbers of breeding California gulls (Larus californicus) and ring-billed gulls (L. delawarensis) declined during the study, mostly because of the abandonment of a large colony in the mid-Columbia River. Three gull colonies below the confluence of the Snake and Columbia rivers increased substantially, however. Factors that may limit colony size and productivity for piscivorous waterbirds nesting on the Columbia Plateau included availability of suitable nesting habitat, interspecific competition for nest sites, predation, gull kleptoparasitism, food availability, and human disturbance. Based on observed population trends alone, there is little reason to project increased impacts to juvenile salmonid survival from tern and cormorant populations. Additional monitoring and evaluation may be warranted to assess future impacts of the growing Badger Island American white pelican colony and those gull colonies located near mainstem dams or associated with Caspian tern colonies where kleptoparasitism is common.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Demographics of piscivorous colonial waterbirds and management implications for ESA-listed salmonids on the Columbia Plateau
Series title Northwest Science
DOI 10.3955/046.088.0408
Volume 88
Issue 4
Year Published 2014
Language English
Publisher Northwest Scientific Association
Contributing office(s) Coop Res Unit Seattle
Description 16 p.
First page 344
Last page 359
Country United States
Other Geospatial Columbia Plateau