Nocturnal body temperature in wintering blue tits is affected by roost-site temperature and body reserves

Abstract

Birds commonly use rest-phase hypothermia, a controlled reduction of body temperature (T(b)), to conserve energy during times of high metabolic demands. We assessed the flexibility of this heterothermic strategy by increasing roost-site temperature and recording the subsequent T(b) changes in wintering blue tits (Cyanistes caeruleus L.), assuming that blue tits would respond to treatment by increasing T(b). We found that birds increased T(b) when roost-site temperature was increased, but only at low ambient temperatures. Moreover, birds with larger fat reserves regulated T(b) at higher levels than birds carrying less fat. This result implies that a roosting blue tit maintains its T(b) at the highest affordable level, as determined by the interacting effect of ecophysiological costs associated with rest-phase hypothermia and energy reserves, in order to minimize potential fitness costs associated with a low T(b).

Individual Variation in Sleep-Wake Rhythms in Free-Living Birds

“…Chronobiol Int Downloaded from informahealthcare.com by Queen's University on 12/27/14 their nocturnal body temperature by a few degrees Celsius during cold winter nights (Nord et al, 2009(Nord et al, , 2011. In support of this explanation, we found a strong relationship between ambient night temperature and rhythmicity.…”

“…An alternative explanation for higher rhythmicity in yearlings could be their potentially larger amount of energy reserves due to their subordinate status (Ekman & Lilliendahl, 1993;Gosler, 1996). Juvenile birds might, therefore, carry higher fat reserves (but see Broggi & Brotons, 2001), which would be consistent with an attenuated hypothermic response (Nord et al, 2011) and increased rhythmicity. In addition to the described environmental and age effects, we found a significant individual-specific component on the level of periodicity.…”

Challenges of measuring body temperatures of free-ranging birds and mammals

“…This fast, affordable, and minimally invasive method relies on inserting a thin temperaturesensitive probe into the rectum via the anus or cloaca [20][21][22]. It is commonly undertaken using thermocouples or thermistors either custom adapted for use or using standard medical or veterinary thermometers.…”

Individual variation in sleep behaviour in blue tits Cyanistes caeruleus: assortative mating and associations with fitness‐related traits

“…Several studies suggest that individuals in better body condition do not sleep as deep as those in poor condition and therefore wake up more often during the night. For example, blue tits that carried less fat reserves reduced their rest‐phase body temperature more than birds with larger fat scores (Nord et al 2011) and lower body temperatures result in higher arousal thresholds and consequently lead to less frequent awakenings (Geiser and Ruf 1995).…”