Experiments were performed on the subtropical tree sparrow (Passer montanus) to investigate whether day length, as a proximate factor, involves circadian rhythm in timing seasonal responses or these events are programmed by the mediation of an endogenous circannual rhythm. The experiments began from the two equinoxes, i.e. March and September, and continued for about 18 months. In each equinox, one group of wild birds of both sex was exposed to near simulated day length as it varies in nature at Shillong (Latitude 25°34'N, Longitude 91°53'E), and the other group was given a photoperiodic treatment in the reverse order corresponding to natural variation in day length from the other equinox. The birds exposed to near simulated day lengths in March and September showed gonadal, bill colour and molting responses, as observed in the wild birds in nature. Moreover, when photosensitive birds of March were given photoperiodic treatment in the reverse order (i.e., natural variation in day lengths beginning from September), they maintained their photosensitivity and responded only when they received increasing day length in the following September. However, when the photorefractory birds of September were exposed to reverse photoperiodic treatment (i.e. natural day length as it varies from March), they terminated their photorefractoriness after receiving decreasing day length in March the next year and responded when they again received increasing day length in the following September. These results strongly suggest that photoperiodic regulation of seasonal responses in the tree sparrow involves an endogenous circadian rhythm and exclude the possibility of circannual rhythm generation.

中文翻译：

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欧亚树麻雀（Passer montanus）的季节性响应的光周期编程中的昼夜节律与昼夜节律。

在亚热带树麻雀（Passer montanus）上进行了实验，以调查日长作为邻近因素在定时季节性响应中是否涉及昼夜节律，或者这些事件是通过内源性昼夜节律的调节来编程的。实验从两个春分点开始，即三月和九月，并持续了大约18个月。在每一个春分点，一组自然界中在西隆（北纬25°34'N，东经91°53'E）自然变化的雌雄同体的野生鸟类接近于模拟的日长，而另一组则受到光周期的影响以相反的顺序进行处理，这与其他昼夜平分点的日长自然变化相对应。在3月和9月暴露于接近模拟日长的鸟类表现出性腺，票据颜色和蜕皮反应，在自然界的野生鸟类中观察到。此外，当以相反的顺序（即，从9月开始的日长自然变化）对3月的光敏鸟进行光周期处理时，它们会保持其光敏性，并且仅在下一个9月收到日长增加时才做出反应。但是，当9月份的耐光鸟类接受反向光周期处理（即自然日长度因3月的变化而变化）时，它们在次年3月的日长度减少后终止了其光耐性，而当他们再次在12月的日长度增加时做出了反应。接下来的九月。