Top–down influence of resident and overwintering Bald Eagles (Haliaeetus leucocephalus) in a model marine ecosystem

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Abstract:

Conservation of predators presents challenges when predators affect prey populations that provide ecosystem services. Near Puget Sound, resident and overwintering populations of Bald Eagle (Haliaeetus leucocephalus (L., 1766)) have expanded in recent decades. We modeled the potential impact of Bald Eagles on marine food-web structure. Bald Eagles caused trophic cascade dynamics through mid-level predators (seabirds) to lower trophic levels (fishes, benthic invertebrates), particularly when seabirds were more abundant in eagle diets. Resident Bald Eagles affected food-web structure more than overwintering eagles, despite the latters’ greater abundance. Predator avoidance behavior by nearshore diving birds and herbivorous birds exacerbated trophic cascade effects, but only in a narrow range of species. Variability in the number of overwintering Bald Eagles, which come to the area to feed on salmon carcasses (primarily chum salmon, Oncorhynchus keta (Walbaum in Artedi, 1792)), had little effect on the food web. Our results indicate that Bald Eagles are important to marine food-web structure, owing to their high consumption rates and the high consumption rates of their seabird prey, but uncertainty about eagle diets limits our full understanding of their impact. In systems where Bald Eagles affect large seabird breeding colonies, their role in food-web structure is likely greater.

Keywords: Anas spp; Bald Eagle (Haliaeetus leucocephalus); Bucephala spp; Larus spp; Melanitta spp; cascades trophiques; food webs; marine community ecology; pygargue à tête blanche (Haliaeetus leucocephalus); réseau trophique; trophic cascades; écologie des communautés marines

Document Type: Research Article

DOI: http://dx.doi.org/10.1139/z2012-059

Affiliations: 1: Conservation Biology Division, Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 2725 Montlake Boulevard East, Seattle, WA 98112, USA. 2: Washington Department of Fish and Wildlife, Wildlife Science Division, 600 Capitol Way North, Olympia, WA 98501, USA.

Publication date: July 22, 2012

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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