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

Birds breeding in the Arctic must carefully balance survival and reproducti on 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, predator s, or low food availability. To examine this relationship, we applied a sta ndardized stressor, capture and handling, to four species of shorebirds (Sc olopacidae) during their breeding season in the Arctic and measured the inc rease in corticosterone between 3 min and 30 min after capture (hereafter c alled the stress response). We tested two hypotheses in an effort to explai n the individual variation observed in the stress response. The first hypot hesis states that individuals most responsible for parental care have a low er stress response than individuals less responsible for parental care. In species with uniparental care (Pectoral Sandpiper Calidris melanotos, Red P halarope Phalaropus fulicaria), the caregivers had a lower stress response than the opposite sex, although in the latter species the difference was no t significant (P = 0.016 and P = 0.102, respectively). In a species with eq ual biparental care (Semipalmated Sandpiper C. pusilla), the stress respons e did not differ between the sexes (P = 0.99, Barrow population). In a spec ies with unequal biparental care (Western Sandpiper C. mauri), the more par ental sex (males) had a much lower stress response than the less parental s ex (P = 0.002). The second hypothesis states that individuals breeding in t he high Arctic have a lower stress response than individuals breeding in th e low Arctic. The stress response in a low-Arctic population of Semipalmate d Sandpipers (Nome) was higher than that in a high-Arctic population (Barro w, P < 0.05). Individuals at an additional high-Arctic location (Prudhoe Ba y) exhibited stress responses most similar to those of the Barrow populatio n (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 a nd under conditions that might be perceived as stressful, if not for their reduced sensitivity to potential stressors. (C) 2001 Academic Press.