724 REPRODUCTION AND MIGRATION IN BIRDS 



By way of comparison, it is of interest to note that our rate-intensity 

 curve for Zonotrichia leucophrys gambelii is somewhat similar to that 

 for egg production in the domestic fowl in which no appreciable in- 

 crease was obtained by increasing intensity from 10 lux (1 ft-c) to 

 330 lux (30 ft-c) (Roberts and Carver, 1941). 



As Burger (1949) has aptly observed, it is essential that studies of 

 the role of light intensity be refined by use of monochromatic or 

 narrow-band light. This is particularly important in view of the differ- 

 ences in response to different parts of the visible spectrum. 



PHOTOPERIODICALLY INDUCED TESTICULAR DEVELOPMENT 

 AS A FUNCTION OF WAVELENGTH 



The early investigations of Bissonnette (1932b,c,d, 1933a,b, 1936, 

 1937; Bissonnette and Wadlund, 1931) demonstrated clearly for 

 Sturnus vulgaris that red light stimulates testicular development 

 whereas green light is ineffective. Burger's (1943) investigations with 

 the same species demonstrated a good response in the range of 0.58 

 to 0.68 micron and that far red and near infrared are nonstimulatory. 

 Similarly, red has been found to be effective and green ineffective in 

 gonadal stimulation in Passer domesticus (Ringoen, 1942) and in the 

 domestic turkey (Scott and Payne, 1937). 



In the domestic fowl, at supramaximal intensities, red light is as 

 effective as white light in maintaining high egg production (Roberts 

 and Carver, 1941). In domestic ducks also it is red light that is most 

 effective in stimulating testicular development (Benoit 1936b, 1938a) 

 with the ran^e of maximum effectiveness being about 0.60 to 0.74 

 micron (Benoit and Ott, 1938, 1944; Benoit, 1950b; Benoit, Walter, 

 and Assenmacher, 1950a, b). It is very important to note that when 

 testicular development is stimulated by conducting light directly to the 

 hypothalamus, yellow, green, and blue are effective; the implications 

 of this will be discussed subsequently. Suffice it to note here that these 

 investigations suggest that photostimulation of gonadal development 

 does not involve entirely the same receptors as are involved in vision; 

 possibly the receptors may be entirely distinct and quite possibly they 

 are, at least in part, nonocular (Benoit, 1950b). 



