772 REPRODUCTION AND MIGRATION IN BIRDS 



1953), In view, however, of the low intensity of white Hght required 

 to maintain production, an analysis of the effects of wavelengths at 

 equal energy levels might prove of interest. 



With supplementary ultraviolet (bactericidal) sources of peak in- 

 tensity at 2537 angstrom units in rooms artificially lighted and from 

 which daylight was excluded, Barott et ah (1951) reported 10 to 

 19% increases in annual production over a period of five years. The 

 effect could not be attributed to bactericidal properties of the lamps 

 nor to elaboration of vitamin D. Carson and Beall (1955), however, 

 using similar sources of ultraviolet to supplement a basic schedule 

 of 14 hr incandescent light daily, found no effect on egg production; 

 these authors suggest that the differing outcome of their experiments 

 may have been due to temperature differences which were conducive, 

 in the tests of Barott et al., to more eflflcient operation of the ultra- 

 violet lamps. 



{d) Photoperiod and activity. For a long time after the effective- 

 ness of supplemental light on egg production had become well known, 

 the additional light was widely believed to afford merely increased 

 opportunity for a special form of activity — feeding. It is of some 

 interest that Goodale (1923) questioned this view in the early 

 twenties. Whetham (1933) suggested stimulation through the anterior 

 pituitary body. About the same time Bissonnette (1933) came to a 

 similar conclusion, reasoning from his experiments on the European 

 starling. 



The stimulatory effects of light were shown by Rider (1938) to be 

 independent of the availability of feed during hours of artificial light- 

 ing. Rider's results were confirmed by Callenbach et al. (1943), who 

 stated that a daily feeding period of 10 hr was adequate for maximal 

 Qgg production. Roberts and Carver (1941) made the interesting ob- 

 servation that hens under 3 hr intermittent illumination daily con- 

 sumed more feed — and produced at a higher rate — than did birds 

 receiving 10-hr continuous light daily. As was noted by Hammond 

 (1954), the stimulatory effects of "shock" lighting, of ultraviolet, and 

 of Piatt's "dim red lights" do not "prolong the period of feeding or 

 of obvious activity." 



