Publication Date


Advisor(s) - Committee Chair

Blaine Ferrell, Gary Dillard, Joe Winstead

Degree Program

Department of Biology

Degree Type

Master of Science


It has been shown in studies involving many temperatezone avian species that annual variation in day length is a major environmental factor influencing the timing of seasonal events such as gonadal development, molt, fat deposition, and migration. The mechanism whereby these birds measure day length involves a circadian rhythm of photosensitivity which is entrained by the daily photoperiod. If light occurs such that it coincides with the photosensitive phase of this rhythm, an event such as gonadal recrudescence is induced. This study was carried out in photosensitive White-throated Sparrows in winter and spring of 1982 to explore the possibility that temperature might modify the expression of the circadian rhythm of testicular photosensitivity. Upon treatment with interrupted-night photoperiods, birds held on LD 9:15 at temperatures averaging 27.6 C exhibited a daily rhythm in testicular photosensitivity, whereas birds held on LD 9:15 at temperatures averaging 3.7 C did not show such a daily rhythm. These results support the hypothesis that temperature modifies the timing of certain seasonal events in the White-throated Sparrow by influencing the expression of a circadian rhythm of photosensitivity.


Biology | Life Sciences

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