Data from: Experimentally increased nest temperature affects body temperature, growth and apparent survival in blue tit nestlings

The thermal environment experienced by birds during early postembryonic development may be an important factor shaping growth and survival. However, few studies have directly manipulated nest temperature (Tn) during the nestling phase, and none have measured the consequences of experimental heat stress on nestlings’ body temperature (Tb). It is therefore not known to what extent any fitness consequences of development in a thermally challenging environment arise as a direct, or indirect, effect of heat stress. We, therefore, studied how experimentally increased Tn affected Tb in 8-12 days old blue tit (Cyanistes caeruleus) nestlings, to investigate if increased thermoregulatory demands to maintain normothermic Tb influenced nestling growth and apparent long-term survival. Nestlings in heated nest-boxes had significantly higher Tb compared to unheated nestlings during most of the experimental period. Yet, despite facing Tn > 50 °C (as measured in the bottom of the nest cup below the nestlings), the highest nestling Tb recorded was 43.8 °C with nestlings showing evidence of controlled facultative hyperthermia without any increased nestling mortality in heated nests. However, body mass gain was lower in these nestlings compared to nestlings from control nest-boxes. Contrary to our prediction, a larger proportion of nestlings from heated nest-boxes were recaptured during their first winter, or subsequently recruited into the breeding population as first- or second-year breeders. This result should, however, be treated with caution because of low recapture rates. This study highlights the importance of the thermal environment during nestling development, and its role in shaping both growth patterns and possibly also apparent survival.

鸟类胚胎发育早期所经历的热环境，可能是影响其生长与存活的关键调控因素之一。然而，目前鲜有研究在雏鸟阶段直接操控巢内温度（nest temperature, Tn），且尚无研究评估实验性热应激对雏鸟体温（body temperature, Tb）的影响。因此，我们尚不明确，在热胁迫环境下发育所带来的适合度相关后果，究竟是热应激的直接效应还是间接效应。为此，本研究以8-12日龄的蓝山雀（Cyanistes caeruleus）雏鸟为实验对象，探究实验性升高巢内温度对雏鸟体温的影响，以此明确维持正常体温所需的体温调节负荷增加，是否会对雏鸟生长及远期表观存活率产生影响。在实验的大部分时段内，加热巢箱中的雏鸟体温显著高于对照巢箱的雏鸟。尽管加热巢箱内的巢温超过50℃（测量点位为雏鸟下方的巢杯底部），但记录到的雏鸟最高体温仅为43.8℃，雏鸟表现出受控的兼性体温过高现象，且加热巢箱内未出现雏鸟死亡率升高的情况。不过，与对照巢箱的雏鸟相比，加热巢箱中的雏鸟体重增量更低。与我们的预测相反，加热巢箱的雏鸟在首个越冬季被重捕的比例更高，且后续有更多个体在1龄或2龄时进入繁殖种群。但由于重捕率较低，该结果需谨慎解读。本研究凸显了雏鸟发育阶段热环境的重要性，及其对生长模式乃至表观存活率的潜在调控作用。