Foraging-Related Activity of Bald Eagles at a Washington Seabird Colony and Seal Rookery

Hayward, James L.; Galusha, Joseph G.; Henson, Shandelle M.

doi:10.3356/jrr-08-107.1

Cited by 33 publications

(31 citation statements)

References 24 publications

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“…The two refuges are closed to the public and cover a combined area of 147 ha. The island serves as the breeding ground for more than 70% of the seabirds in the Puget Sound area and is an important rookery for harbor seals (Hayward et al []). Gravel spits project from each end of the island: Violet Point on the east end and Kanem Point on the southwest end.…”

Section: Methodsmentioning

confidence: 99%

A METHOD FOR PREDICTING HARBOR SEAL (PHOCA VITULINA) HAULOUT AND MONITORING LONG‐TERM POPULATION TRENDS WITHOUT TELEMETRY

Cowles

Henson²,

Hayward

et al. 2013

Natural Resource Modeling

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Abstract. Monitoring population trends in harbor seals (Phoca vitulina) generally involves two steps: (i) a census obtained from aerial surveys of haul-out sites, and (ii) an upward correction based on the proportion of seals hauled out as estimated from a sample of telemetry-tagged seals. Here we present a mathematical method for obtaining site-specific correction factors without telemetry. The method also determines site-specific environmental factors associated with haulout and provides algebraic equations that predict diurnal haul-out numbers and correction factors as functions of these variables. We applied the method at a haul-out site on Protection Island, Washington, USA. The haul-out model and correction factor model were functions of tide height, current velocity, and time of day, and the haul-out model explained 46% of the observed variability in diurnal haul-out dynamics. Although the particular models are site-specific, the general model and methods are portable. A suite of such models for haul-out sites of a regional stock would allow managers to monitor long-term population trends without telemetry.

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Section: Methodsmentioning

confidence: 99%

A METHOD FOR PREDICTING HARBOR SEAL (PHOCA VITULINA) HAULOUT AND MONITORING LONG‐TERM POPULATION TRENDS WITHOUT TELEMETRY

Cowles

Henson²,

Hayward

et al. 2013

Natural Resource Modeling

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“…They may also prey upon smaller avian species, particularly Larus spp. (e.g., Murie 1940, Todd et al 1982, Buchanan and Watson 2010, Hayward et al 2010) that frequent these sites (Burger and Gochfeld 1983, Belant et al 1995, Caron-Beaudoin et al 2013.…”

Section: Discussionmentioning

confidence: 99%

Landfill Use by Bald Eagles in the Chesapeake Bay Region

Turrin

Watts

Mojica

2015

Journal of Raptor Research

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“…During the 1980s, few eagle disturbances of the gull colony on Protection Island's Violet Point were noted, and from 1980 to 1993 gull nest numbers increased by 37% (3,796–5,189; Table ). Beginning in the 1990s, however, a dramatic rise in bald eagle activity over and within the colony was observed (Galusha & Hayward, ; Hayward et al, ), with a significant decline in numbers of breeding gulls at the site (Cowles et al, ). Bald eagles constitute the only significant source of interspecific predation on the gulls in this colony (Hayward et al, ).…”

Section: Introductionmentioning

confidence: 99%

Predator–prey dynamics of bald eagles and glaucous‐winged gulls at Protection Island, Washington, USA

Henson

Desharnais

Funasaki

et al. 2019

Ecology and Evolution

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Bald eagle ( Haliaeetus leucocephalus ) populations in North America rebounded in the latter part of the twentieth century, the result of tightened protection and outlawing of pesticides such as DDT. An unintended consequence of recovery may be a negative impact on seabirds. During the 1980s, few bald eagles disturbed a large glaucous‐winged gull ( Larus glaucescens ) colony on Protection Island, Washington, USA, in the Salish Sea. Breeding gull numbers in this colony rose nearly 50% during the 1980s and early 1990s. Beginning in the 1990s, a dramatic increase in bald eagle activity ensued within the colony, after which began a significant decline in gull numbers. To examine whether trends in the gull colony could be explained by eagle activity, we fit a Lotka–Volterra‐type predator–prey model to gull nest count data and Washington State eagle territory data collected in most years between 1980 and 2016. Both species were assumed to grow logistically in the absence of the other. The model fits the data with generalized R 2 = 0.82, supporting the hypothesis that gull dynamics were due largely to eagle population dynamics. Point estimates of the model parameters indicated approach to stable coexistence. Within the 95% confidence intervals for the parameters, however, 11.0% of bootstrapped parameter vectors predicted gull colony extinction. Our results suggest that the effects of bald eagle activity on the dynamics of a large gull colony were explained by a predator–prey relationship that included the possibility of coexistence but also the possibility of gull colony extinction. This study serves as a cautionary exploration of the future, not only for gulls on Protection Island, but for other seabirds in the Salish Sea. Managers should monitor numbers of nests in seabird colonies as well as eagle activity within colonies to document trends that may lead to colony extinction.

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Foraging-Related Activity of Bald Eagles at a Washington Seabird Colony and Seal Rookery

Abstract: BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Cited by 33 publications

References 24 publications

A METHOD FOR PREDICTING HARBOR SEAL (PHOCA VITULINA) HAULOUT AND MONITORING LONG‐TERM POPULATION TRENDS WITHOUT TELEMETRY

A METHOD FOR PREDICTING HARBOR SEAL (PHOCA VITULINA) HAULOUT AND MONITORING LONG‐TERM POPULATION TRENDS WITHOUT TELEMETRY

Landfill Use by Bald Eagles in the Chesapeake Bay Region

Predator–prey dynamics of bald eagles and glaucous‐winged gulls at Protection Island, Washington, USA

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