752 REPRODUCTION AND MIGRATION IN BIRDS 



30 days (Kirkpatrick, 1955). Sperm are produced at a threshold 

 between 0.1 and 1.0 ft-c. The principle of the dark-period interrup- 

 tion has been demonstrated by others (Farner et al., 1953; Jenner 

 and Engels, 1952). Farner's group took exception to the idea that 

 the dark period plays an active role in inhibiting a reproductive 

 response, and hypothesized that a light interruption merely augments 

 a carry-over period of gonadotropic activity following the photo- 

 period. However this controversy may be resolved, it is clear that full 

 sexual activity or no sexual activity results from the same number of 

 light hours by varying the length of the dark period. 



In various experiments the interrupted dark period technique has 

 been used for stimulating the growth of gonadal tissue in quail in 

 which age, environmental temperature, and breeding history have 

 been the variables. The experiments considered here were under- 

 taken to determine whether a refractory period is characteristic of 

 female quail. Data were obtained from groups of females of different 

 ages, and from similarly aged birds having different breeding histories 

 or postlaying rest periods. 



The refractory period has been variously defined, but the aspects 

 of it as stated by Miller (1954) for perching birds will suffice for 

 our purposes. Refractoriness is characterized by the regression of 

 the gonads from the breeding state even under prolonged treatment 

 with long daily light periods; and resting birds in regression may fail 

 to respond to light stimulation if they have not been inactive long 

 enough. Thus the refractory period seems to fulfill a requirement for 

 rest and inactivity, following natural or induced reproductive activity, 

 before breeding is possible again. The length of the refractory interval 

 has been determined for juncos (Wolfson, 1952) and white-crowned 

 sparrows (Farner and Mewaldt, 1955). Although refractoriness is 

 usually measured by the gonad response to stimulation, the gonado- 

 tropic role of the pituitary is an essential part of the response 

 mechanism (Farner and Mewaldt, 1955), and the swelling gonad 

 may indirectly manifest the pituitary response. If the gonad fails to 

 enlarge, however, there might be some question as to whether the 

 gonadotropic action of the pituitary alone was inhibited, the gonad 

 response, or both. 



Nearly all experiments with refractoriness have been devoted to 



