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Evidence of facultative daytime hypothermia in a small passerine wintering at northern latitudes
Author(s) -
Lewden Agnès,
Petit Magali,
Milbergue Myriam,
Orio Stéphane,
Vézina François
Publication year - 2014
Publication title -
ibis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.933
H-Index - 80
eISSN - 1474-919X
pISSN - 0019-1019
DOI - 10.1111/ibi.12142
Subject(s) - passerine , daytime , foraging , hypothermia , biology , basal metabolic rate , facultative , zoology , ecology , physiology , atmospheric sciences , endocrinology , geology
The use of hypothermia as a means to save energy is well documented in birds. This energy‐saving strategy is widely considered to occur exclusively at night in diurnally active species. However, recent studies suggest that facultative hypothermia may also occur during the day. Here, we document the use of daytime hypothermia in foraging Black‐capped Chickadees Poecile atricapillus wintering in eastern Canada. We measured the body temperature ( T b ) of 126 individuals (plus 48 repeated measures) during a single winter and related values to ambient temperature ( T a ) at the time of capture. We also tested whether daytime hypothermia was correlated with the size of body reserves (residuals of mass on structural size and fat score) and levels of metabolic performance (basal metabolic rate and maximum thermogenic capacity). We found that T b of individual birds was lower when captured at low T a , reaching values as low as 35.5 °C in actively foraging individuals. T b was unrelated to metabolic performance or measures of body reserves. Therefore, daytime hypothermia does not result from individuals being unable to maintain T b during cold spells or to a lack of body reserves. Our data also demonstrated a high level of individual variation in the depth of hypothermia, the causes of which remain to be explored.