title: The stress hormone corticosterone in a marine top predator reflects short-term changes in food availability.
abstract: In many seabird studies, single annual proxies of prey abundance have been used to explain variability in breeding performance, but much more important is probably the timing of prey availability relative to the breeding season when energy demand is at a maximum. Until now, intraseasonal variation in prey availability has been difficult to quantify in seabirds. Using a state-of-the-art ocean drift model of larval cod Gadus morhua, an important constituent of the diet of common guillemots Uria aalge in the southwestern Barents Sea, we were able to show clear, short-term correlations between food availability and measurements of the stress hormone corticosterone (CORT) in parental guillemots over a 3-year period (2009-2011). The model allowed the extraction of abundance and size of cod larvae with very high spatial (4 km) and temporal resolutions (1 day) and showed that cod larvae from adjacent northern spawning grounds in Norway were always available near the guillemot breeding colony while those from more distant southerly spawning grounds were less frequent, but larger. The latter arrived in waves whose magnitude and timing, and thus overlap with the guillemot breeding season, varied between years. CORT levels in adult guillemots were lower in birds caught after a week with high frequencies of southern cod larvae. This pattern was restricted to the two years (2009 and 2010) in which southern larvae arrived before the end of the guillemot breeding season. Any such pattern was masked in 2011 by already exceptionally high numbers of cod larvae in the region throughout chick-rearing period. The findings suggest that CORT levels in breeding birds increase when the arrival of southern sizable larvae does not match the period of peak energy requirements during breeding.
authors: Department of Natural Sciences, Tromsø University Museum PO Box 6050 Langnes, Tromsø, NO-9037, Norway.
authors: Robert T
authors: RT
authors: Barrett
authors: Norwegian Institute for Nature Research, FRAM - High North Research Centre for Climate and the Environment Tromsø, NO-9296, Norway ; Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology Trondheim, NO-7049, Norway.
authors: Kjell E
authors: KE
authors: Erikstad
authors: Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology Trondheim, NO-7049, Norway.
authors: Hanno
authors: H
authors: Sandvik
authors: Institute of Marine Research PO Box 1870 Nordnes, Bergen, NO-5817, Norway.
authors: Mari
authors: M
authors: Myksvoll
authors: Swiss Ornithological Institute Sempach, CH-6204, Switzerland.
authors: Susi
authors: S
authors: Jenni-Eiermann
authors: Norwegian Institute for Nature Research, FRAM - High North Research Centre for Climate and the Environment Tromsø, NO-9296, Norway.
authors: Ditte L
authors: DL
authors: Kristensen
authors: Marine Genomics Research Group, Faculty of Biosciences and Aquaculture, University of Nordland Bodø, NO-8049, Norway.
authors: Truls
authors: T
authors: Moum
authors: Department of Natural Sciences, Tromsø University Museum PO Box 6050 Langnes, Tromsø, NO-9037, Norway ; Norwegian Institute for Nature Research, FRAM - High North Research Centre for Climate and the Environment Tromsø, NO-9296, Norway.
authors: Tone K
authors: TK
authors: Reiertsen
authors: Institute of Marine Research PO Box 1870 Nordnes, Bergen, NO-5817, Norway.
authors: Frode
authors: F
authors: Vikebø
keywords: CORT; Common guillemot; Uria aalge; food availability; seabird