Meeting Abstract
During summer in the high Arctic (71.29°N, 156.79°W) the sun does not set for >2 months. Therefore, migratory, arctic-breeding birds experience 24h of constant light during their breeding season. Among those migrants are two sympatric species that, while in the same family and can interbreed, differ in life-history traits. Lapland longspurs (Lapponicus calcarius) are monogamous and nest on the open tundra whereas snow buntings (Plectrophenax nivalis) nest in cavities and engage in extra-pair matings. Both species retain diurnal activity patterns during the polar day, and become quiescent between 00:00 and 04:00. To determine whether there is a circadian rhythm in the adrenocortical response to stress, free-living birds of both species were captured during the nesting stage and held at the following time points to collect blood samples: baseline (<2min post-trap), 10min post-trap and 30 min post-trap. Plasma was then assayed for corticosterone concentration using ELISA. For both species, no discernible circadian rhythms were detected in baseline corticosterone levels. However, snow buntings displayed a trend for increased stress-induced corticosterone (30min) as the polar day progressed (Circwave harmonic regression, p = 0.089). While preliminary, this study suggests that a lack of circadian variation in ground-nesting Lapland longspurs may represent an adaptation to round-the-clock predation pressures experienced at their nests.
