The large communal nests of sociable weavers provide year-round insulated refuge for weavers and pygmy falcons

The primary role of nests as structural support for eggs, nestlings, and incubating parents is well established, but our understanding of their secondary roles and their adaptive features is still limited. Nests can serve a particularly important role in protecting or buffering birds from weather. In hot, arid environments, maximum daily temperatures can exceed a species’ upper critical temperature threshold and during the nonbreeding season temperatures may also drop below freezing. Nest structures that help buffer against extreme temperatures may play a crucial role in managing the costs of thermoregulation, especially those nests that are used and maintained year-round. We use extensive year-round data to investigate the thermal benefits of massive colonial structures built by sociable weavers in the arid savannahs of the Kalahari, South Africa. These colonies consist of multiple nesting chambers and are used as roosts when birds are not breeding. We explored whether these structures provide thermal buffering throughout the year and how individual chamber placement within the colony and features of the chambers influenced their thermal buffering capacity. We also investigated whether nest chambers occupied and modified by an obligate nest parasite, the African pygmy falcon provided additional thermal buffering. Our results show that sociable weaver colonies provide thermal benefits throughout the year, buffering both hot and cold ambient extremes. Chambers with longer entrance tunnels provided better insulation than chambers with shorter entrance tunnels, and chambers located toward the center of a colony provided greater insulation than chambers at the edge. Chambers occupied by falcons did not display additional thermal benefits, which may be due to falcons choosing chambers with shorter entrance tunnels. Because falcons are larger than weavers, they may find it harder to enter chambers with longer entrance tunnels, and/or because weavers cease maintenance of those chambers. In conclusion, the communal nests of sociable weaver provide thermal benefits to weavers and heterospecifics alike, creating a more optimal environment for breeding, roosting and reducing thermal stress. In a landscape that is becoming increasingly harsh under climate change, the importance of these structures to the local animal communities may also increase.
(Paper provisionally
accepted to Frontiers in Ecology and Evolution. DOI to follow.)

鸟巢作为卵、雏鸟以及孵卵亲鸟的结构支撑这一核心功能已得到广泛证实，但学界对其次要功能与适应性特征的认知仍较为有限。
鸟巢在帮助鸟类抵御或缓冲天气影响方面可发挥尤为关键的作用。在炎热干旱的环境中，日最高气温可能超过某一物种的临界高温阈值，而非繁殖季的气温也可能降至冰点以下。能够缓冲极端温度的巢结构，在管理体温调节的成本方面可能起到至关重要的作用，尤其是那些全年被使用并维护的巢穴。
本研究依托全面的全年数据，探究了南非喀拉哈里干旱稀树草原中群居织鸟（Sociable Weaver）所建造的大型集群巢结构的热效益。这类集群巢包含多个巢室，在鸟类非繁殖期被用作栖息处。我们探讨了这些结构是否能全年提供热缓冲效应，以及集群内单个巢室的位置与巢室特征如何影响其热缓冲能力。
我们还调查了专性巢寄生鸟类——非洲侏儒隼（African Pygmy Falcon）所占据并改造的巢室是否能提供额外的热缓冲效应。研究结果表明，群居织鸟的集群巢全年均可提供热效益，能够缓冲环境中的极端高温与极端低温。
入口隧道更长的巢室比入口更短的巢室隔热效果更佳，而位于集群中心的巢室的隔热性能也优于边缘位置的巢室。被非洲侏儒隼占据的巢室并未展现出额外的热效益，这可能是因为隼类选择了入口隧道更短的巢室：由于隼类比织鸟体型更大，它们更难进入入口隧道较长的巢室；也有可能是因为织鸟会停止对这类巢室的维护。
综上，群居织鸟的公共巢不仅为织鸟自身，也为其他异种生物（heterospecifics）提供了热效益，为繁殖、栖息创造了更优的环境，并降低了热应激风险。在气候变化导致生境日益严苛的背景下，这类巢结构对当地动物群落的重要性或也将进一步提升。
（本文已暂获《生态学与进化前沿》（Frontiers in Ecology and Evolution）收录，DOI将后续公布。）