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.

鸟类胚胎发育后早期阶段所经历的热环境，或是塑造其生长与存活的关键影响因子。然而，目前鲜有研究在雏鸟阶段直接操控巢内温度（nest temperature, Tn），且尚无研究量化实验性热应激对雏鸟体温（body temperature, Tb）的影响。因此，目前仍不清楚，在热胁迫环境下发育所带来的适合度相关后果，在多大程度上是热应激的直接或间接作用所致。为此，本研究以8-12日龄的蓝山雀（Cyanistes caeruleus）雏鸟为对象，探究实验性升高的巢温对其体温的影响，以明确维持正常体温所需增加的体温调节负荷，是否会对雏鸟的生长及表观长期存活产生作用。在实验的大部分时段内，加热巢箱中的雏鸟体温显著高于未加热对照组巢箱中的雏鸟。尽管加热组的巢温超过50℃（测量点位位于雏鸟下方的巢杯底部），但记录到的雏鸟最高体温仅为43.8℃，且雏鸟表现出受控的兼性体温升高迹象，同时加热巢内的雏鸟死亡率并未出现上升。不过，与对照组雏鸟相比，加热组雏鸟的体重增长速率更低。与我们的预测相反，加热组巢箱中雏鸟在首个越冬季被再次捕获的比例更高，且后续有更多个体在1龄或2龄时加入繁殖种群。但由于重捕率较低，对该结果的解读需持谨慎态度。本研究凸显了雏鸟发育阶段热环境的重要性，以及其对雏鸟生长模式乃至表观存活的调控作用。