title: Foraging responses of black-legged kittiwakes to prolonged food-shortages around colonies on the Bering Sea shelf.
abstract: We hypothesized that changes in southeastern Bering Sea foraging conditions for black-legged kittiwakes (Rissa tridactyla) have caused shifts in habitat use with direct implications for population trends. To test this, we compared at-sea distribution, breeding performance, and nutritional stress of kittiwakes in three years (2008-2010) at two sites in the Pribilof Islands, where the population has either declined (St. Paul) or remained stable (St. George). Foraging conditions were assessed from changes in (1) bird diets, (2) the biomass and distribution of juvenile pollock (Theragra chalcogramma) in 2008 and 2009, and (3) eddy kinetic energy (EKE; considered to be a proxy for oceanic prey availability). In years when biomass of juvenile pollock was low and patchily distributed in shelf regions, kittiwake diets included little or no neritic prey and a much higher occurrence of oceanic prey (e.g. myctophids). Birds from both islands foraged on the nearby shelves, or made substantially longer-distance trips overnight to the basin. Here, feeding was more nocturnal and crepuscular than on the shelf, and often occurred near anticyclonic, or inside cyclonic eddies. As expected from colony location, birds from St. Paul used neritic waters more frequently, whereas birds from St. George typically foraged in oceanic waters. Despite these distinctive foraging patterns, there were no significant differences between colonies in chick feeding rates or fledging success. High EKE in 2010 coincided with a 63% increase in use of the basin by birds from St. Paul compared with 2008 when EKE was low. Nonetheless, adult nutritional stress, which was relatively high across years at both colonies, peaked in birds from St. Paul in 2010. Diminishing food resources in nearby shelf habitats may have contributed to kittiwake population declines at St Paul, possibly driven by increased adult mortality or breeding desertion due to high foraging effort and nutritional stress.
authors.affiliation: Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon, United States of America.
authors.forename: Rosana
authors.initials: R
authors.lastname: Paredes
authors.affiliation: Ocean Sciences Department, University of California Santa Cruz, Santa Cruz, California, United States of America.
authors.forename: Rachael A
authors.initials: RA
authors.lastname: Orben
authors.affiliation: Department of Fisheries and Wildlife, Oregon State University, Hatfield Marine Science Center, Newport, Oregon, United States of America.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Suryan
authors.affiliation: U.S. Fish and Wildlife Service, Anchorage, Alaska, United States of America.
authors.forename: David B
authors.initials: DB
authors.lastname: Irons
authors.affiliation: U.S. Geological Survey-Oregon Cooperative Fish and Wildlife Research Unit, Oregon State University, Corvallis, Oregon, United States of America.
authors.forename: Daniel D
authors.initials: DD
authors.lastname: Roby
authors.affiliation: Environmental Science Department, Alaska Pacific University, Anchorage, Alaska, United States of America.
authors.forename: Ann M A
authors.initials: AM
authors.lastname: Harding
authors.affiliation: Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska, United States of America.
authors.forename: Rebecca C
authors.initials: RC
authors.lastname: Young
authors.affiliation: College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon, United States of America.
authors.forename: Kelly
authors.initials: K
authors.lastname: Benoit-Bird
authors.affiliation: Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle, Washington, United States of America.
authors.forename: Carol
authors.initials: C
authors.lastname: Ladd
authors.affiliation: Alaska Maritime National Wildlife Refuge, U.S. Fish and Wildlife Service, Homer, Alaska, United States of America.
authors.forename: Heather
authors.initials: H
authors.lastname: Renner
authors.affiliation: Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon, United States of America.
authors.forename: Scott
authors.initials: S
authors.lastname: Heppell
authors.affiliation: British Antarctic Survey, Natural Environment Research Council, Cambridge, United Kingdom.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Phillips
authors.affiliation: Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska, United States of America.
authors.forename: Alexander
authors.initials: A
authors.lastname: Kitaysky
mesh_terms: D000162:Acoustics; D000413:Alaska; D000818:Animals; D018533:Biomass; D001947:Breeding; D046091:Charadriiformes / Q000502:physiology*; D004032:Diet; D005247:Feeding Behavior; D020387:Food Chain; D056084:Genetic Fitness; D062312:Islands; D016014:Linear Models; D009792:Oceans and Seas; D011235:Predatory Behavior / Q000502:physiology; D014872:Water Movements