Call it the bird version of yoga. Red crossbills (Loxia curvirostra), small, yellow-breasted songbirds hailing from the western United States, keep mellow for the sake of their offspring. During chilly months when the living gets tough, reproductively active crossbills tend to have fewer stress hormones—or corticosterones—churning through their veins than their nonrambunctious counterparts, researchers report online today in Biology Letters. This absence makes sense: Stress hormones can give critters a survival edge by, for instance, helping birds and other animals tap their sugar stores. But this stress response is also inherently selfish. Birds with too much corticosterone often abandon their nests, leaving offspring to the elements. Crossbills may thus dampen the flow of stress hormones to ensure that their chicks survive, risking their own health in the process. If only they could learn the warrior pose.
See more ScienceShots.