Late breeding usually occurs during years of poor environmental conditions, but the proximate mechanisms underlying this phenological pattern have been poorly documented.In this study reasearchers combined the deployment of GPS devices (from 2008 to 2010) and the monitoring of breeding parameters and baseline corticosterone levels (from 2007 to 2011) to investigate the proximate regulation of breeding date in a population of black-legged kittiwake.

The timing of breeding varied considerably during the course of the study and late breeding was associated with reduced clutch size and low breeding success at the individual level. Trips lasted longer and were to greater distances in 2009, the year of late breeding, compared to 2008 and 2010, highlighting a food scarcity in 2009. Corticosterone levels differed among years, and were the lowest in 2010, the year of earliest breeding. 2009 var et år med lite mat, det resulterte i at fuglene foretok lengre turer, både i tid og rom, samt en sen hekking. Det var en betydelig variasjon i stressnivåene fra år til år, med lavest nivå i 2010, som også var året med tidligst hekking og de korteste turene.

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Breeding decision and laying date were not related to corticosterone levels at the individual level, but were positively influenced by body condition, suggesting that complex proximate mechanisms may affect timing of breeding in kittiwakes.

Contact person: Børge Moe, NINA

Photo: Børge Moe