Researchers curious about how small birds in the wild manage to survive cold winter nights have used miniature temperature transmitters and data loggers to solve the puzzle.<\/p>\n
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Prior to the study the researchers, from Â鶹ֱ²¥ and The University of Western Australia, suspected that like many small mammals the birds entered torpor \u2013 a period of lethargy \u2013 to lower their body temperatures and conserve energy to both survive the cold and cope with scarce food supplies during winter.<\/p>\n
However co-author Dr Christine Cooper, of Curtin\u2019s Department of Environment and Agriculture, said that after monitoring a population of White-browed babblers in a Western Australian forest for two consecutive winters, the researchers found that instead, the birds \u2013 which weigh on average about 46.5g \u2013 kept themselves warm by huddling in groups in tightly insulated nests.<\/p>\n
\u201cInsect-eating birds might be expected to use torpor in winter, like many mammals, because they\u2019re small and lose heat easily. Their food is less abundant and they are inactive at night when it\u2019s cold,\u201d Dr Cooper said<\/p>\n
\u201cBut even though babblers have characteristics that should make them perfect candidates for torpor, our research shows they rely instead on a combination of clever nest construction and communal lifestyles to maintain a body temperature of around 40.3C, even when it is below freezing outside the nest.\u201d<\/p>\n
The babblers were radio-tracked in the field at Dryandra Woodland south of Perth, and their body temperature measured remotely using temperature-sensitive transmitters.<\/p>\n
The researchers also placed temperature loggers in the babblers\u2019 nests to determine how cold they got. In the laboratory, they measured the birds\u2019 overnight energy expenditure at different temperatures by analysing how much oxygen they used.<\/p>\n
\u201cWe found they have low resting energy requirements and roost in large social groups in insulated, almost enclosed stick nests,\u201d Dr Cooper said.<\/p>\n
\u201cThis effectively halved their energy losses, allowing them to conserve 35-45 per cent of the energy consumed by individual birds. It played a big role in helping them to balance their daily energy budget and apparently negated any need for torpor.<\/p>\n
\u201cWe now have a better understanding of the energy requirements of birds and their ability to keep their body temperature constant under different environmental conditions.<\/p>\n
\u201cIt means we can better predict how temperature can impact on these birds.\u201d<\/p>\n