Thermoregulatory costs of the innate immune response are modulated by winter food availability in a small passerine

1. In winter, a challenge to the immune system could pose a major energetic trade-off for small endotherms, whereby increasing body temperature (Tb; i.e. eliciting fever) may be beneficial to fight off invading pathogens yet incur a cost for vital energy-saving mechanisms.
2. Having previously shown that the availability and acquisition of energy, through manipulation of food predictability, influence the depth of rest-phase hypothermia in a wild bird in winter, we expected that the nocturnal thermoregulatory component of the acute-phase immune response would also be modulated by food availability.
3. By manipulating winter food availability in the wild for great tits, Parus major, we created an area offering a “predictable” and constant supply of food at feeding stations, while an unmanipulated area was subject to naturally “unpredictable” food. Birds were subject to an immune challenge shortly after dusk, and the thermoregulatory response was quantified via continuous recording of noc..., Body temperature data from roosting great tits (Parus major) was recorded using Biomark HDR Plus with standard racket antenna and thermo-sensitive passive integrated transponders (BioTherm 13, Biomark, US) located subcutaneously. Body temperature was measured every minute during the night, either following arousal, handling and immune challenge in birds subject to predictable or unpredictable food availability (Tb_food_manipulation.csv) or following only arousal and handling (Tb_control.csv). Body temperature data were processed to derive 10-minute and 60-minute rolling means. Ambient temperature data were collected using iButtons (DS 1922L, Maxim Integrated, US). For full methods, refer to the published article.,