Charadriiform Birds in Antarctica: Behavioral, Morphological, and Physiological Adjustments Conserving Reproductive Success

Abstract

Birds colonizing different climates must alter some aspect of their breeding biology to maintain successful reproduction. Comparative analyses were used to elucidate the changes in parental behavior and in the rate of development of the young associated with successful breeding of charadriiform birds in Antarctica. The species studied, the kelp gull Larus dominicanus, the South Polar skua Catharacta maccormicki, and the greater sheathbill Chionis alba, represent three of the four independent colonizations of Antarctica by charadriiform birds. Antarctic species brooded their young two to five times longer than did their temperate relatives. The Antarctic young had greater tolerance to hypothermia, which suggests that, historically, parental care failed to protect the young from selection by low temperatures. Antarctic hatchlings were neither larger nor metabolically more mature than their relatives. Despite presumed selection on the young by low temperatures and the presence of individual variation in development, the young did not attain homeothermy significantly earlier than did their temperate relatives. Growth rates over the entire nestling period were also similar for Antarctic and temperate species. The Antarctic young did grow faster to a moderate size more favorable for thermoregulation and showed coordinately faster development of resting metabolic rate. South Polar skuas, from the oldest Antarctic lineage, further diverged in having accelerated development of thermogenesis, which substantially reduced their reliance on parental brooding. Evolutionary changes in physiological development of the young have resulted in improved abilities to tolerate hypothermia and in lower costs, relative to peak metabolic rates, to maintain homeothermy.