Are corticosterone levels a good indicator of food availability and reproductive performance in a kittiwake colony? Richard B. Lanctot, a, * Scott A. Hatch, a Verena A. Gill, a,1 and Marcel Eens b a U.S. Geological Survey, Alaska Science Center, 1011 E. Tudor Road, MS 701, Anchorage, AK 99503, USA b Department of Biology, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium Received 13 February 2002; revised 23 December 2002; accepted 6 January 2003 Abstract We evaluated the use of corticosterone to gauge forage availability and predict reproductive performance in black-legged kittiwakes (Rissa tridactyla) breeding in Alaska during 1999 and 2000. We modeled the relationship between baseline levels of corticosterone and a suite of individual and temporal characteristics of the sampled birds. We also provided supplemental food to a sample of pairs and compared their corticosterone levels with that of pairs that were not fed. Corticosterone levels were a good predictor of forage availability in some situations, although inconsistencies between corticosterone levels and reproductive performance of fed and unfed kittiwakes suggested that this was not always the case. In general, higher corticosterone levels were found in birds that lacked breeding experience and in birds sampled shortly after arriving from their wintering grounds. All parameters investigated, however, explained only a small proportion of the variance in corticosterone levels. We also investigated whether corticosterone, supplemental feeding, year of the study, breeding experience, body weight, and sex of a bird were able to predict laying, hatching, and fledging success in kittiwakes. Here, breeding experience, year of the study, and body weight were the best predictors of a bird’s performance. Corticosterone level and supplemental feeding were good predictors of kittiwake reproductive performance in some cases. For example, corticosterone levels of birds sampled during the arrival stage reliably predicted laying success, but were less reliable at predicting hatching and fledging success. Counts of active nests with eggs or chicks may be more reliable estimates of the actual productivity of the colony. Supplemental feeding had strong effects on kittiwake productivity when natural forage was poor, but had little effect when natural forage was plentiful. © 2003 Elsevier Science (USA). All rights reserved. Keywords: Alaska; Breeding performance; Corticosterone; Forage; Hormone; Kittiwake; Rissa tridactyla; Stress; Supplemental feeding Animals are thought to respond to unpredictable and disruptive change in their environment by modifying their behavior to promote survival. Behavior modification can include increased foraging, cessation of territoriality, re- duced feeding or abandonment of young, and irruptive mi- gration (Astheimer, Buttemer, and Wingfield, 1992; Sil- verin, 1998; Wingfield, Hunt, Breuner, Dunlap, Fowler, Freed, and Lepson, 1997). This behavior modification is thought to occur through the rapid activation of adrenocor- tical tissue that results in an increase of circulating glu- cocorticosteroids (Harvey, Phillips, Rees, and Hall, 1984). Measurement of circulating levels of glucocorticosteroids in free-living animals can provide a method for determining whether an individual is stressed and for monitoring ani- mals’ response to unpredictable and disruptive environmen- tal change (Wingfield et al., 1997). Recently, field endocrinologists have suggested the use of circulating levels of corticosterone as a gauge of forage availability and a predictor of reproductive performance in seabirds (Wingfield et al., 1997; Kitaysky, Wingfield, and Piatt, 1999). Because reproductive performance appears to be closely tied to forage availability in seabirds (Baird, 1990; Cairns, 1987; Gill, Hatch, and Lanctot, 2002), it seems reasonable to expect seabirds living in poor food * Corresponding author. Current address: USFWS, Migratory Bird Management, 1011 East Tudor Road, MS 201, Anchorage, AK 99503, USA. Fax: +1-907-786-3641. E-mail address: Richard_Lanctot@fws.gov (R.B. Lanctot). 1 Current address: U.S. Fish and Wildlife Service, Marine Mammals Management, 1011 E. Tudor Road, MS 341, Anchorage, AK 99503, USA. R Available online at www.sciencedirect.com Hormones and Behavior 43 (2003) 489 –502 www.elsevier.com/locate/yhbeh 0018-506X/03/$ – see front matter © 2003 Elsevier Science (USA). All rights reserved. doi:10.1016/S0018-506X(03)00030-8