Ecological factors underlying the adrenocortical response to capture stress in arctic-breeding shorebirds

Birds breeding in the Arctic must carefully balance survival and reproduction because of the often extreme environmental conditions and the very brief breeding season. Acute elevation of plasma corticosterone is one mechanism that birds apparently use to alter the balance in favor of survival at the expense of reproduction when faced with stressors such as storms, predators, or low food availability. To examine this relationship, we applied a standardized stressor, capture and handling, to four species of shorebirds (Scolopacidae) during their breeding season in the Arctic and measured the increase in corticosterone between 3 min and 30 min after capture (hereafter called the stress response). We tested two hypotheses in an effort to explain the individual variation observed in the stress response. The first hypothesis states that individuals most responsible for parental care have a lower stress response than individuals less responsible for parental care. In species with uniparental care (Pectoral Sandpiper Calidris melanotos, Red Phalarope Phalaropus fulicaria), the caregivers had a lower stress response than the opposite sex, although in the latter species the difference was not significant (P = 0.016 and P = 0.102, respectively). In a species with equal biparental care (Semipalmated Sandpiper C. pusilla), the stress response did not differ between the sexes (P = 0.99, Barrow population). In a species with unequal biparental care (Western Sandpiper C. mauri), the more parental sex (males) had a much lower stress response than the less parental sex (P = 0.002). The second hypothesis states that individuals breeding in the high Arctic have a lower stress response than individuals breeding in the low Arctic. The stress response in a low-Arctic population of Semipalmated Sandpipers (Nome) was higher than that in a high-Arctic population (Barrow, P < 0.05). Individuals at an additional high-Arctic location (Prudhoe Bay) exhibited stress responses most similar to those of the Barrow population (P > 0.05). Taken together, these results provide evidence of a mechanism that birds may use to breed in environments with a brief breeding season and under conditions that might be perceived as stressful, if not for their reduced sensitivity to potential stressors.