 Further, body mass declines throughout nocturnal torpor at a rate of 0.04 g per hour, amounting to about 10% of weight loss each night.The circulating hormone, corticosterone, is one signal that arouses a hummingbird from torpor.Use and duration of torpor vary among hummingbird species and are affected by whether a dominant bird defends territory, with nonterritorial subordinate birds having longer periods of torpor.