ИСТИНА

Scarlet-backed flowerpecker (Dicaeidae, Passeriformes) is among the smallest passerine birds. We studied the energetics of free-living tropical birds in the Cat Tien National Park (south of Vietnam) and found that the resting metabolic rate (RMR) of scarlet-backed flowerpeckers was very low, 1.57 mlO2/gh on average (the avg. morning body weight was 5.0 g). The flowerpeckers’ RMR value was 2.6 times lower than the expected basal metabolic rate (BMR) from a general passerine scaling curve (McNab, 2009) and 3 times lower than the BMR of the Van Hasselt’s sunbird (Leptocoma brasiliana), which is equal in size (based on our data from the same study location). The sample size included 4 RMR measurements from 3 individuals (one individual was recaptured and re-measured 2 years after the first RMR measurement). The dramatically low RMR of scarlet-backed flowerpeckers could be an evidence of torpor, a state, which is very rare in passerines compared to some other avian orders. An interesting feature of this species is the ability to enter torpor at relatively high ambient temperature (Ta). We did not measure the body temperature of individuals, but it could not be lower than 28 C, because we performed respirometry within the thermoneutral zone of most tropical birds (Ta = 27-28 C). We suppose that the peculiarity of scarlet-backed flowerpeckers’ energetics relates to their diet. Despite their small size, flowerpeckers feed mainly on plant foods, such as berries, nectar, and green seeds.