DSI-NRF Centre of Excellence, FitzPatrick Institute of African Ornithology, University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa.
Department of Zoology and Entomology, DSI-NRF Centre of Excellence at the FitzPatrick Institute, University of Pretoria, Pretoria, 0002, South Africa.
Oecologia. 2020 May;193(1):225-235. doi: 10.1007/s00442-020-04644-6. Epub 2020 Apr 15.
During hot weather, terrestrial animals often seek shaded thermal refugia. However, this can result in missed foraging opportunities, loss of body condition and impaired parental care. We investigated whether such costs could compromise breeding success in a widespread southern African bird: the Southern Yellow-Billed Hornbill Tockus leucomelas. We predicted that hornbills might be especially vulnerable to temperature-dependant reductions in parents' foraging capacity due to extreme asymmetry in sex-specific roles during breeding: females are confined within the nest cavity for most of the nesting period and the burden of provisioning falls solely on the male during this time. We followed 50 hornbill nesting attempts in the Kalahari Desert between 2012 and 2015, collecting data on provisioning rates, adult and nestling body mass, fledging success and size of fledglings. Mean daily maximum air temperatures (T) during nesting attempts ranged from 33.2 to 39.1 °C. The likelihood of successful fledging fell below 50% at mean T > 35.1 °C; a threshold now regularly exceeded at our study site due to recent climate warming. Additionally, offspring fledging following the hottest nesting attempts were > 50% lighter than those fledging following the coolest. Sublethal costs of keeping cool including loss of body condition, production of poor-quality offspring and breeding failure are likely to become issues of serious conservation concern as climate change progresses; even for currently widespread species. Missed-opportunity costs associated with behavioral thermoregulation and direct sublethal costs of temperature exposure should not be overlooked as a potential threat to populations, especially in environments that are already hot.
在炎热的天气里，陆生动物通常会寻找遮荫的热避难所。然而，这可能导致觅食机会的错失、身体状况的下降和亲代照顾的受损。我们研究了这种代价是否会影响一种广泛分布于南非的鸟类——南非黄嘴犀鸟 Tockus leucomelas 的繁殖成功。我们预测，由于繁殖期间雌雄两性在角色上的极端不对称，导致父母的觅食能力受温度依赖性降低，犀鸟可能特别容易受到影响：雌鸟在巢腔内的大部分繁殖期都被限制，而在这段时间里，喂养的负担完全落在雄鸟身上。我们在 2012 年至 2015 年间，在卡拉哈里沙漠跟踪了 50 次犀鸟筑巢尝试，收集了喂养率、成鸟和雏鸟的体重、育雏成功率以及雏鸟的大小等数据。筑巢尝试期间的日平均最高空气温度（T）范围从 33.2 到 39.1°C。在平均 T > 35.1°C 时，成功育雏的可能性低于 50%；由于最近的气候变暖，我们的研究地点现在经常超过这个阈值。此外，在最热的筑巢尝试后育雏的后代比在最冷的筑巢尝试后育雏的后代轻 > 50%。保持凉爽的亚致死代价，包括身体状况的下降、产生低质量后代和繁殖失败，随着气候变化的推进，很可能成为严重的保护关注问题；即使对于目前广泛分布的物种也是如此。由于行为性体温调节而错失的机会成本和直接暴露于高温的亚致死成本，不应被忽视，因为它们可能成为种群的潜在威胁，尤其是在已经炎热的环境中。
