Résumé
‘Fight-or-flight’ stress responses allow animals to cope adaptively tosudden threats by mobilizing energy resources and priming the bodyfor action. Because such responses can be costly and redirectbehavior and energy from reproduction to survival, they are likely to beshaped by specific life-history stages, depending on the availableenergy resources and the commitment to reproduction. Here, weconsider how heart rate (HR) responses to acute stressors areaffected by the advancing breeding season in a colonial seabird, theking penguin (Aptenodytes patagonicus). We subjected 77 birds (44males, 33 females) at various stages of incubation and chick-rearingto three experimental stressors (metal sound, distant approach andcapture) known to vary both in their intensity and associated risk, andmonitored their HR responses. Our results show that HR increase inresponse to acute stressors was progressively attenuated with thestage of breeding from incubation to chick-rearing. Stress responsesdid not vary according to nutritional status or seasonal timing(whether breeding was initiated early or late in the season), butwere markedly lower during chick-rearing than during incubation.This pattern was obvious for all three stressors. We discuss how‘fight-or-flight’ responses may be modulated by considering theenergy commitment to breeding, nutritional status and reproductivevalue of the brood in breeding seabirds.