Like many other animals, white-tailed antelope squirrels exhibit a bimodal daily pattern of activity in the field during the summer. Because seasons in the field involve not only changes in ambient temperature but also changes in photoperiod and food availability, the cause of the bimodal pattern is not known. In this study, behavioral activity of white-tailed antelope squirrels was studied under controlled environmental conditions in the laboratory. Without the rise in ambient temperature around noontime, the activity pattern was unimodal under a summer-like photoperiod, and this was so when activity was monitored either with running wheels or with infrared motion detectors. Some of the animals exhibited several bouts of activity each day, but the bouts were not uniform in timing or duration, so that the activity pattern of the whole group was unmistakably unimodal with a peak or plateau at noontime. Thus, the bimodal pattern observed in the field in this species is not due to an intrinsic property of the circadian system or to the presence of a long photoperiod but likely to the heat of summer noontime.

中文翻译：

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稳定环境条件下羚羊地松鼠活动的单峰日分布

像许多其他动物一样，夏季，白尾羚羊松鼠在田间表现出双峰的日常活动模式。由于田间季节不仅涉及环境温度的变化，而且还涉及光周期和食物供应量的变化，因此双峰模式的原因尚不清楚。在这项研究中，在受控环境条件下在实验室中研究了白尾羚羊松鼠的行为活动。在中午前后环境温度没有升高的情况下，活动模式在像夏天这样的光周期下是单峰的，因此当通过运行轮或红外运动检测器监视活动时，活动模式就是这样。有些动物每天表现出数次活动，但活动时间或持续时间不一致，因此，整个组的活动模式无疑是单峰的，在中午时达到高峰或高原。因此，在该物种的田野中观察到的双峰模式不是由于昼夜节律系统的固有特性，也不是由于存在长的光周期，而是由于夏季中午的高温。