MEPS 352:221-234 (2007)  -  DOI:

Seabirds as indicators of marine food supplies: Cairns revisited

John F. Piatt1,*, Ann M. A. Harding1,2, Michael Shultz1, Suzann G. Speckman3, Thomas I. van Pelt1, Gary S. Drew1, Arthur B. Kettle4

1US Geological Service Alaska Science Center, 1011 E. Tudor Rd., Anchorage, Alaska 99503, USA
2Alaska Pacific University, Environmental Science Department, 4101 University Dr., Anchorage, Alaska 99508, USA
3School of Aquatic and Fishery Sciences, University of Washington, 1122 NE Boat St., Seattle, Washington 98105, USA
4Alaska Maritime National Wildlife Refuge, US Fish and Wildlife Service, 2355 Kachemak Bay Dr., Homer, Alaska 99603, USA

ABSTRACT: In his seminal paper about using seabirds as indicators of marine food supplies, Cairns (1987, Biol Oceanogr 5:261–271) predicted that (1) parameters of seabird biology and behavior would vary in curvilinear fashion with changes in food supply, (2) the threshold of prey density over which birds responded would be different for each parameter, and (3) different seabird species would respond differently to variation in food availability depending on foraging behavior and ability to adjust time budgets. We tested these predictions using data collected at colonies of common murre Uria aalge and black-legged kittiwake Rissa tridactyla in Cook Inlet, Alaska. (1) Of 22 seabird responses fitted with linear and non-linear functions, 16 responses exhibited significant curvilinear shapes, and Akaike’s information criterion (AIC) analysis indicated that curvilinear functions provided the best-fitting model for 12 of those. (2) However, there were few differences among parameters in their threshold to prey density, presumably because most responses ultimately depend upon a single threshold for prey acquisition at sea. (3) There were similarities and some differences in how species responded to variability in prey density. Both murres and kittiwakes minimized variability (CV < 15%) in their own body condition and growth of chicks in the face of high annual variability (CV = 69%) in local prey density. Whereas kittiwake breeding success (CV = 63%, r2 = 0.89) reflected prey variability, murre breeding success did not (CV = 29%, r2 < 0.00). It appears that murres were able to buffer breeding success by reallocating discretionary ‘loafing’ time to foraging effort in response (r2 = 0.64) to declining prey density. Kittiwakes had little or no discretionary time, so fledging success was a more direct function of local prey density. Implications of these results for using ‘seabirds as indicators’ are discussed.

KEY WORDS: Ecological indicators · Seabirds · Food availability · Threshold · Functional response · Predator–prey dynamics

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Cite this article as: Piatt JF, Harding AMA, Shultz M, Speckman SG, van Pelt TI, Drew GS, Kettle AB (2007) Seabirds as indicators of marine food supplies: Cairns revisited. Mar Ecol Prog Ser 352:221-234.

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