Data from: The use of the nest for parental roosting and thermal consequences of the nest for nestlings and parents

At temperate latitudes, altricial birds and their nestlings need to handle night temperatures well below thermoneutrality during the breeding season. Thus, energy costs of thermoregulation might constrain nestling growth, and low nocturnal temperatures might require resources that parents could otherwise have invested into nestlings during the day. To manipulate parental work rate, we performed brood size manipulations in breeding marsh tits (Poecile palustris). Nest box temperatures were always well above ambient temperature and increased with increasing brood size. In line with predictions, a large majority of females (but no males) made use of this benign environment for roosting. Furthermore, females tending enlarged broods, thereby having to work harder during the day, reduced their body temperature at night. This might have reduced nocturnal energy expenditure. Our finding that a higher proportion of enlarged, as compared to control, females continued to use the nest box as roosting sites even after a simulated predation event despite increased vulnerability to predation, further highlighting the need for energy conservation in this group. High nest box attendance and reduced body temperature in brood-reduced females may indicate that these females prioritised self-maintenance by initiating other costly physiological adjustments, e.g. moult, when relieved from parental work. We suggest that the energy demand for defending homeothermy is an element of the general trade-off between current and future reproduction, i.e. between daytime investment in food provisioning and the potential short- and long-term costs of a reduction in body temperature and increased predation risk.

在温带纬度地区，晚成雏鸟类（altricial birds）及其雏鸟在繁殖季需应对远低于热中性区（thermoneutrality）的夜间气温。因此，体温调节的能量成本可能会限制雏鸟的生长，而夜间低温可能会消耗亲鸟本可在日间投入给雏鸟的资源。为操控亲鸟的工作负荷，我们对繁殖中的沼泽山雀（Poecile palustris）开展了育雏规模操控（brood size manipulations）实验。巢箱（nest box）内温度始终显著高于环境温度，且随育雏规模扩大而升高。与预测相符的是，绝大多数雌鸟（无雄鸟）会利用这一适宜环境进行夜间栖息（roosting）。此外，抚育更大育雏群、因而日间需付出更多辛劳的雌鸟，会在夜间降低自身体温，这或许能减少夜间的能量消耗。我们的研究发现，相较于对照组，更多育雏规模被扩大的雌鸟在模拟捕食事件（simulated predation event）后，仍会继续将巢箱作为栖息位点——即便此时其面临的捕食风险升高——这进一步凸显了该类群个体对能量节约的迫切需求。育雏规模被缩减的雌鸟会频繁使用巢箱且体温降低，这或许表明这些亲鸟在脱离育雏负担后，会通过启动其他高成本的生理调节，例如换羽（moult），来优先保障自身维护。我们提出，维持恒温性（homeothermy）的能量需求，是当前繁殖与未来繁殖之间普遍权衡的一部分，即权衡日间的食物投喂投入，与降低体温和升高捕食风险所带来的短期及长期成本。