Heat tolerance for many birds under climate and land use change scenarios could be compromised in the future. Common Nighthawks (Chordeiles minor) belong to the Caprimulgiformes, a generally heat-tolerant order, but few studies have assessed heat tolerance in Caprimulgiform chicks, which might be particularly susceptible to heat stress. In the midwestern United States, nighthawks primarily nest on flat graveled rooftops in urban areas, as natural nesting habitats are limited. Urban rooftop-nesting nighthawks are likely exposed to higher environmental temperatures than birds nesting at more thermally buffered natural sites, and evaporative cooling might be impeded by the typically high summer humidity in their Midwest breeding range. This combination of heat and humidity might negatively impact heat tolerance of nighthawk chicks. We exposed 7- to 14-day-old nighthawk chicks (n = 15) from rooftop nests to ambient temperatures (Tas) up to 51°C and at typical summer dew points. Chicks initiated gular flutter at a mean ambient temperature of 42.4 ± 3.4°C (mean ± SE). Evaporative water loss (EWL) rates increased significantly with increasing temperature above 44.0 ± 1.5°C. Chicks showed little evidence of lower and upper bounds of the thermal neutral zone over the range of temperatures (30–44°C) for which we measured oxygen consumption. Body mass loss was significantly positively correlated with temperature during heat exposure trials. Chicks tolerated Tas up to 51°C and body temperatures (Tbs) up to 48°C, which, along with the high temperatures at which gular flutter and high rates of EWL were initiated, suggest that nighthawk chicks are tolerant of high ambient temperatures, even with relatively high humidity. Given the high rates of mass loss and high Tbs at hot ambient temperatures, chick heat tolerance mechanisms could be detrimental for rooftop-nesting nighthawks given projected increasing trends for both heat and humidity in the midwestern United States.

中文翻译：

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城市屋顶筑巢的普通夜鹰雏鸡通过热疗耐受高温，蒸发失水率相对较低

未来气候和土地利用变化情景下许多鸟类的耐热性可能会受到影响。普通夜鹰（Chordeiles minor）属于 Caprimulgiformes，通常是耐热的目，但很少有研究评估 Caprimulgiform 雏鸡的耐热性，这可能特别容易受到热应激的影响。在美国中西部，由于自然筑巢栖息地有限，夜鹰主要在城市地区平坦的砾石屋顶上筑巢。城市屋顶筑巢的夜鹰可能比在更热缓冲的自然地点筑巢的鸟类暴露在更高的环境温度下，并且蒸发冷却可能会受到中西部繁殖范围内典型的夏季高湿度的阻碍。这种热量和湿度的组合可能会对夜鹰雏鸡的耐热性产生负面影响。我们将 7 至 14 天大的夜鹰雏鸡 (n = 15) 从屋顶巢穴暴露在高达 51°C 的环境温度 (Tas) 和典型的夏季露点。雏鸡在 42.4 ± 3.4°C（平均值 ± SE）的平均环境温度下开始了侧翼颤动。随着温度升高到 44.0 ± 1.5°C 以上，蒸发水分损失 (EWL) 率显着增加。在我们测量耗氧量的温度范围内（30-44°C），小鸡几乎没有证据表明热中性区的下限和上限。在热暴露试验期间，体重减轻与温度显着正相关。雏鸡可耐受高达 51°C 的 Tas 和高达 48°C 的体温 (Tbs)，再加上引发镜面扑动和高 EWL 发生率的高温，表明夜鹰雏鸡能够耐受高环境温度，即使湿度相对较高。鉴于高温环境温度下的高质量损失率和高 Tbs，鉴于美国中西部热量和湿度的预计增长趋势，雏鸡耐热机制可能对屋顶筑巢的夜鹰有害。