Foraging Ecology of Bald Eagles in the Columbia River Estuary

Watson, James; Garrett, Monte G.; Anthony, Robert G.

doi:10.2307/3808981

Cited by 50 publications

(38 citation statements)

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“…Our data on diets and productivity were spatially extensive and spanned the critical time period of sea otter abundance and subsequent decline, thus providing evidence for these indirect effects. In addition, Bald Eagles are opportunistic in their foraging habits (Watson et al 1991), and their diets reflect the abundance and availability of their prey within the limits of their ability to capture such prey (Buehler 2000). Consequently, we believe that the changes in diets we observed reflected the influence of sea otters on the abundance of the eagle's prey in the nearshore marine ecosystem.…”

Section: Discussionmentioning

confidence: 73%

“…At least two such changes were evident in our dietary data. First, large numbers of smooth lumpsuckers briefly appeared in shallow coastal waters across the central and western Aleutians during the late winter/ early spring of 1991-1992and 1992(Watt et al 2000. A similar phenomenon was reported in the mid-1960s (Kenyon 1969).…”

Section: Discussionmentioning

confidence: 99%

“…They have relatively small breeding territories and tend to remain on these territories year-round, provided the surrounding water bodies do not freeze during winter (Garrett et al 1993). Because their breeding territories are small, they have evolved as opportunistic feeders (Watson et al 1991), and their diets reflect the abundance of prey that are available to them (Buehler 2000). As a result, their diets tend to be diverse, and they show a remarkable level of dietary plasticity from one region to another.…”

Section: Introductionmentioning

confidence: 99%

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Bald Eagles and Sea Otters in the Aleutian Archipelago: Indirect Effects of Trophic Cascades

Anthony

Estes

Ricca

et al. 2008

Ecology

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Abstract. Because sea otters (Enhydra lutris) exert a wide array of direct and indirect effects on coastal marine ecosystems throughout their geographic range, we investigated the potential influence of sea otters on the ecology of Bald Eagles (Haliaeetus leucocephalus) in the Aleutian Islands, Alaska, USA. We studied the diets, productivity, and density of breeding Bald Eagles on four islands during 1993-1994 and 2000-2002, when sea otters were abundant and scarce, respectively. Bald Eagles depend on nearshore marine communities for most of their prey in this ecosystem, so we predicted that the recent decline in otter populations would have an indirect negative effect on diets and demography of Bald Eagles. Contrary to our predictions, we found no effects on density of breeding pairs on four islands from 1993-1994 to 2000-2002. In contrast, diets and diet diversity of Bald Eagles changed considerably between the two time periods, likely reflecting a change in prey availability resulting from the increase and subsequent decline in sea otter populations. The frequency of sea otter pups, rock greenling (Hexagammus lagocephalus), and smooth lumpsuckers (Aptocyclus ventricosus) in the eagle's diet declined with corresponding increases in Rock Ptarmigan (Lagopus mutus), Glaucous-winged Gulls (Larus glaucescens), Atka mackerel (Pleurogrammus monopterygius), and various species of seabirds during the period of the recent otter population decline. Breeding success and productivity of Bald Eagles also increased during this time period, which may be due to the higher nutritional quality of avian prey consumed in later years. Our results provide further evidence of the wide-ranging indirect effects of sea otter predation on nearshore marine communities and another apex predator, the Bald Eagle. Although the indirect effects of sea otters are widely known, this example is unique because the food-web pathway transcended five species and several trophic levels in linking one apex predator to another.

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Section: Discussionmentioning

confidence: 73%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Bald Eagles and Sea Otters in the Aleutian Archipelago: Indirect Effects of Trophic Cascades

Anthony

Estes

Ricca

et al. 2008

Ecology

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“…Effects of human activity Anthony and Isaacs 1989 McGarigal et al 1991 Energetics and communal roosting Keister et al 1985 Environmental contaminants Frenzel and Anthony 1989Anthony et al 1993Buck et al 2005 Frenzel 1985 Food habits Isaacs and Anthony 1987Frenzel and Anthony 1989DellaSala et al 1989Watson et al 1991 Isaacs et al1993 Isaacs et al1996Marr et al 1995McShane et al 1998 Frenzel 1985 Habitat management Anderson 1971Anderson 1985Arnett et al 2001Isaacs et al 2005 Home range and habitat use Garrett et al 1993Frenzel 1988 Frenzel 1985 Midwinter population [1979][1980][1981][1982][1983] Opp 1979 Keister et al1987Frenzel and Anthony 1989DellaSala et al 1989Isaacs and Anthony 1987 Isaacs et al1993 Isaacs et al1996Tressler et al 1999 Fleischer 2005 1 The private category (n = 637) consisted of many different owners including individuals, local businesses, and multinational corporations (96%); and a Native American tribe, power companies, an irrigation district, and a conservation organization (4%).…”

Section: Acknowledgementsmentioning

confidence: 99%

Coming to Terms About Describing Golden Eagle Reproduction

Steenhof¹,

Kochert

McIntyre

et al. 2017

Journal of Raptor Research

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“…Mersmann (1989) documented seasonal shifts in prey abundance and foraging habits within the population. Fish are a primary food source for Bald Eagles both within the Chesapeake Bay (Cline andClark 1981, Mersmann 1989) and in many other populations (e.g., Watson et al 1991, Brown 1993. Fish availability within the Chesapeake Bay declines from October through March, with one study documenting a decrease in gillnet sampling catch rates at 0.6-m depth from a monthly average of 3-7 fish/hr from April through September to 0-1 fish/hr from January through March (Mersmann 1989).…”

Section: Discussionmentioning

confidence: 99%