Modulation of heart rate response to acute stressors throughout the breeding season in the king penguin Aptenodytes patagonicus
Résumé
‘Fight-or-flight’ stress responses allow animals to cope adaptively to
sudden threats by mobilizing energy resources and priming the body
for action. Because such responses can be costly and redirect
behavior and energy from reproduction to survival, they are likely to be
shaped by specific life-history stages, depending on the available
energy resources and the commitment to reproduction. Here, we
consider how heart rate (HR) responses to acute stressors are
affected by the advancing breeding season in a colonial seabird, the
king penguin (Aptenodytes patagonicus). We subjected 77 birds (44
males, 33 females) at various stages of incubation and chick-rearing
to three experimental stressors (metal sound, distant approach and
capture) known to vary both in their intensity and associated risk, and
monitored their HR responses. Our results show that HR increase in
response to acute stressors was progressively attenuated with the
stage of breeding from incubation to chick-rearing. Stress responses
did not vary according to nutritional status or seasonal timing
(whether breeding was initiated early or late in the season), but
were 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 the
energy commitment to breeding, nutritional status and reproductive
value of the brood in breeding seabirds.