Sharpe Lynda L, Bayter Camilo, Gardner Janet L
Division of Ecology and Evolution, Research School of Biology, Australian National University, RN Robertson Building 46 Sullivans Creek Rd.Acton 2601, Canberra, ACT, Australia.
Division of Ecology and Evolution, Research School of Biology, Australian National University, RN Robertson Building 46 Sullivans Creek Rd.Acton 2601, Canberra, ACT, Australia.
J Therm Biol. 2021 May;98:102921. doi: 10.1016/j.jtherbio.2021.102921. Epub 2021 Apr 1.
Global warming and intensifying extreme heat events may affect avian reproductive success and costs, particularly in hot, arid environments. It is unclear how breeding birds alter their behaviour in response to rapid climate change, and whether such plasticity will be sufficient to offset rising temperatures. We examine whether a small, open-cup nesting, passerine - the Jacky Winter Microeca fascinans - in semi-arid Australia, exhibits similar levels of behavioural plasticity when incubating under high temperatures as low, and how heat impacts upon parental effort, body mass change and reproductive success. At high temperatures, female effort increased. Females doubled nest attendance between 28 °C and 40 °C, switching from incubating to shading eggs at approx. 30 °C. Egg-shading females panted to avoid hyperthermia. Panting increased with temperature and sun exposure. Male breeding effort was linked to temperature extremes. In cold conditions, males provisioned their mates heavily, buffering females from additional energetic costs, and males suffered a loss of body mass. In extreme heat, males helped shade eggs (although they never incubated). The likelihood of male egg-shading increased with temperature, but level of contribution was positively related to sun exposure. Hatching success declined with air temperatures >35 °C. Egg mortality reached 100 at air temperatures >42.5 °C. Parents continued to attend unviable eggs (for up to two weeks), suggesting egg-loss from heat exposure is a recent phenomenon. Although pairs exhibited considerable behavioural plasticity - including positioning nests to maximize afternoon shade - this was insufficient to counter extreme temperatures. In 2019, one hot day (45 °C) effectively terminated reproduction two months early, and was associated with a 50% decrease in reproductive success. The increasing frequency, intensity and earlier arrival of extreme heat events is likely to pose a major threat to avifauna populations in hot, arid environments, due to increased parental costs, reduced reproductive success and direct mortality.
全球变暖和极端高温事件加剧可能会影响鸟类的繁殖成功率和成本，在炎热干旱的环境中尤其如此。目前尚不清楚繁殖期的鸟类如何应对快速的气候变化来改变其行为，以及这种可塑性是否足以抵消气温上升的影响。我们研究了澳大利亚半干旱地区一种小型的、开放式杯状巢的雀形目鸟类——褐背细尾鹩莺（Microeca fascinans），在高温下孵化时是否表现出与低温时相似程度的行为可塑性，以及高温如何影响亲代投入、体重变化和繁殖成功率。在高温下，雌鸟的投入增加。在28℃至40℃之间，雌鸟的巢中停留时间翻倍，在约30℃时从孵卵转为给卵遮荫。给卵遮荫的雌鸟会喘气以避免体温过高。喘气频率随温度和阳光照射增加。雄鸟的繁殖投入与极端温度有关。在寒冷条件下，雄鸟大量给配偶提供食物，减轻雌鸟额外的能量消耗，雄鸟体重减轻。在酷热天气下，雄鸟会帮忙给卵遮荫（尽管它们从不孵卵）。雄鸟给卵遮荫的可能性随温度增加，但贡献程度与阳光照射呈正相关。当气温高于35℃时，孵化成功率下降。当气温高于42.5℃时，卵死亡率达到100%。亲鸟会继续照料无法存活的卵（长达两周），这表明因热暴露导致的卵损失是近期出现的现象。尽管配对的亲鸟表现出相当大的行为可塑性——包括将巢穴放置在能获得最大午后遮荫的位置——但这不足以抵御极端温度。2019年，一个炎热的日子（45℃）有效地使繁殖提前两个月终止，并导致繁殖成功率下降了50%。由于亲代成本增加、繁殖成功率降低和直接死亡，极端高温事件频率、强度的增加以及更早到来，可能会对炎热干旱环境中的鸟类种群构成重大威胁。
