Hawkshaw Deborah M, Wijmenga Jan J, Mathot Kimberley J
Department of Biological Sciences, University of Alberta, CW 405, Biological Sciences Building, Edmonton, Alberta, T6G 2E9, Canada.
Department of Biological Sciences, University of Alberta, CW 405, Biological Sciences Building, Edmonton, Alberta, T6G 2E9, Canada.
J Therm Biol. 2025 Jan;127:104059. doi: 10.1016/j.jtherbio.2025.104059. Epub 2025 Jan 23.
Small birds in winter can mitigate energetic shortfalls via increases in foraging and/or via controlled reductions in metabolic rate and body temperature (torpor). The ability to both increase foraging and use torpor during the day could have profound implications for an individual's daily energy budget and overwinter survival. Trade-offs between foraging efficiency and daytime torpor use may exist but have not been explicitly investigated. Here, we investigated the presence of within- and among-individual correlations between daytime body temperature (T a proxy for torpor use) and foraging in overwintering black-capped chickadees (Poecile atricapillus). Using temperature-sensing passive integrated transponder tags, we measured daytime T and foraging in 20 free-living chickadees over 49 days in a single winter (January-February). Chickadees generally exhibited T around normothermic levels with an average T during visits to the feeder of 41.7 °C, though T ranged between 25.0 and 44.9 °C. Chickadees exhibited moderately lower daytime T, shorter time intervals between successive feeder visits (IVI), and increased feeder visits as ambient temperature decreased. However, within individuals there was only evidence of a weak positive correlation between visit T and IVI, and no correlation between daily feeder visits and daily mean visit T We found that visit T, daily mean visit T and daily feeder visits were repeatable, while IVI was not. Sex did not explain a significant amount of variation in total daily feeder visits or daytime T, nor was there evidence of among-individual correlations between daily mean visit T and daily feeder visits. Our results suggests that chickadees may independently regulate foraging and diurnal T. Overall, our study provides insights into how small birds in winter can use multiple strategies to overcome energetic challenges. Future studies investigating diurnal torpor and its integration with other strategies are needed to further elucidate how small birds survive harsh winter conditions.
冬季的小型鸟类可以通过增加觅食和/或通过控制降低代谢率及体温（蛰伏）来缓解能量短缺。在白天既能增加觅食又能利用蛰伏的能力可能对个体的每日能量预算和越冬生存产生深远影响。觅食效率与白天蛰伏利用之间可能存在权衡，但尚未得到明确研究。在此，我们研究了越冬黑头山雀（Poecile atricapillus）白天体温（T，蛰伏利用的一个指标）与觅食之间个体内和个体间的相关性。我们使用温度感应被动集成应答器标签，在一个冬季（1月至2月）的49天里测量了20只自由生活的山雀的白天体温和觅食情况。山雀的体温通常维持在常温水平左右，在拜访喂食器期间的平均体温为41.7℃，不过体温范围在25.0℃至44.9℃之间。随着环境温度降低，山雀的白天体温适度降低，连续拜访喂食器的时间间隔（IVI）缩短，且拜访喂食器的次数增加。然而，在个体内部，仅存在拜访体温与IVI之间微弱的正相关证据，且每日拜访喂食器次数与每日平均拜访体温之间无相关性。我们发现拜访体温、每日平均拜访体温和每日拜访喂食器次数具有可重复性，而IVI不具有可重复性。性别并不能解释每日拜访喂食器总次数或白天体温的显著差异，也没有证据表明每日平均拜访体温与每日拜访喂食器次数之间存在个体间相关性。我们的结果表明，山雀可能独立调节觅食和日间体温。总体而言，我们的数据为冬季小型鸟类如何利用多种策略克服能量挑战提供了见解。未来需要开展研究调查日间蛰伏及其与其他策略的整合情况，以进一步阐明小型鸟类如何在严酷的冬季条件下生存。
