Basal metabolic rate of the black-faced sheathbill (Chionis minor) : intraspecific variation in a phylogenetically distinct island endemic

摘要

Metabolic rate is a fundamental characteristic of all organisms.It covaries most significantly with activity, body mass, seasonality,and temperature. Nonetheless, substantial additional variationin metabolic rate, especially either resting rate or basal rate,is associated with a range of factors including phylogenetic position,ecological distinctiveness, range position, and diet. Understandingthis variation is a key goal of physiological ecology.The black-faced sheathbill is a phylogenetically distinct, highlatitude,island-endemic bird occurring exclusively on severalarchipelagos in the southern Indian Ocean. Here we examinedthe idea that the unique phylogenetic position and ecology ofthe black-faced sheathbill may lead to a basal metabolic rate(BMR) different from that predicted by its body mass. Whencompared with BMR data available for all birds and a subsetof island species, it was clear that the BMR of the black-facedsheathbill on subantarctic Marion Island, estimated at 157C usingindirect calorimetry (2.3705 0.464 W, mean5SD; n 22),for a group of birds with a mean mass of 459 + 64 g, is nodifferent from that expected based on body mass. However,variation in BMR, associated with habitat use and diet, evenwhen correcting for variation in mass, was found. Sheathbillsforaging year-round in comparatively resource-rich king penguincolonies have a higher BMR (2.758 5 0.291 W, n 12)than sheathbills that split their foraging between rockhopperpenguin colonies and the intertidal zone (2.04750.303 W, n 10), which are poorer in resources. Because these populationscoexist at relatively small spatial extents (the entire island is290 km2), other factors seem unlikely as causes of this variation.