A frequent response of organisms to climate change is altering the timing of reproduction, and advancement of reproductive timing has been a common reaction to warming temperatures in temperate regions. We tested whether this pattern applied to two common North American turtle species over the past three decades in Nebraska, USA. The timing of nesting (either first date or average date) of the Common Snapping Turtle (Chelydra serpentina) was negatively correlated with mean December maximum temperatures of the preceding year and mean May minimum and maximum temperatures in the nesting year and positively correlated with precipitation in July of the previous year. Increased temperatures during the late winter and spring likely permit earlier emergence from hibernation, increased metabolic rates and feeding opportunities, and accelerated vitellogenesis, ovulation, and egg shelling, all of which could drive earlier nesting. However, for the Painted Turtle (Chrysemys picta), the timing of nesting was positively correlated with mean minimum temperatures in September, October, December of the previous year, February of the nesting year, and April precipitation. These results suggest warmer fall, and winter temperature may impose an increased metabolic cost to painted turtles that impedes fall vitellogenesis, and April rains may slow the completion of vitellogenesis through decreased basking opportunities. For both species, nest deposition was highly correlated with body size, and larger females nested earlier in the season. Although average annual ambient temperatures have increased over the last four decades of our overall fieldwork at our study site, spring temperatures have not yet increased, and hence, nesting phenology has not advanced at our site for Chelydra. While Chrysemys exhibited a weak trend toward later nesting, this response was likely due to increased recruitment of smaller females into the population due to nest protection and predator control (Procyon lotor) in the early 2000s. Should climate change result in an increase in spring temperatures, nesting phenology would presumably respond accordingly, conditional on body size variation within these populations.

中文翻译：

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气候对内布拉斯加海龟筑巢物候的影响

生物体对气候变化的频繁反应正在改变繁殖的时机，而繁殖时机的发展已成为温带地区温度升高的常见反应。我们测试了这种模式是否适用于过去三十年来美国内布拉斯加州的两种北美常见龟种。普通鳄龟（Chelydra serpentina）筑巢的时间（初次或平均））与上一年的12月平均最高温度，嵌套年份的5月的最低和最高温度均呈负相关，与上一年7月的降水量呈正相关。冬末和春季温度的升高可能会使冬眠更早地出现，新陈代谢率和摄食机会的增加，以及加速卵黄发生，排卵和脱壳的过程，所有这些都可能导致更早的筑巢。但是，对于彩绘龟（Chrysemys picta），筑巢时间与上一年9月，10月，12月，筑巢2月和4月降水的平均最低气温呈正相关。这些结果表明秋天变暖，而冬季温度可能会增加彩绘龟的代谢成本，从而阻碍秋天的卵黄发生，而四月的降雨可能会通过减少晒太阳的机会而减慢卵黄发生的完成。对于这两个物种，巢的沉积都与体型高度相关，较大的雌性在本季节早期筑巢。尽管在我们研究现场的整个实地调查的过去四十年中，年平均环境温度有所增加，但春季温度尚未升高，因此，在我们的Chelydra地点筑巢物候尚未发展。而Chrysemys表现出向后期筑巢的弱势趋势，这种反应很可能是由于2000年代初由于筑巢保护和捕食者控制（Procyon lotor）而招募了较小的雌性进入种群。如果气候变化导致春季温度升高，则根据这些种群中个体大小的变化，巢状物候可能会做出相应反应。