TESTES OF TRANSEQUATORIAL MIGRANTS 761 



presumably is complete before the onset of the northward migration. 

 Another molt follows the breeding season, the new plumage being 

 essentially like that worn by the female the year around. Our observa- 

 tions with caged birds suggest that the control of the male nuptial 

 plumage is independent of the testis, developing regularly in alterna- 

 tion with "henny" plumage, as in the African weaver finches studied 

 by Witschi (1955). 



In addition to the cock plumage, the sexually active male has a 

 deeply pigmented, jet black beak (in contrast to the light brown or 

 horn-colored beak of the female and the sexually inactive male 

 designated as neutral in Tables I and II). This beak pigmentation is 



Table I. Summary of Experiments with Male Bobolinks Captured during North- 

 ward Migration in Early May, 1955 (35° 47' N. Lat.) and Exposed to 16-hr Photo- 

 periods until September 15 (Two males in each group) 



Group Photoperiods Beak Color Left Testes June 1 



A 14 hr Remained neutral 1.6 mm^, inactive 



Sept. 15 — June 1 



B 10 hr 1 black, March 23 180 mm^, sperm bun- 

 Sept. 15 — Dec. 21 (fading June 1); dies 

 14 hr both black March 30 

 Dec. 21 — June 1 



C 12 hr Pigment began mid- 8.0 mm', 1st meiotic 



Sept. 15 — June 1 May; black June 1 division 



controlled apparently by the male sex hormone (as in the domestic 

 sparrow and some other birds). Daily intramuscular injection of 

 20 Mg of testosterone propionate resulted in diffuse pigmentation of 

 the beak in about 5 days, both in females and sexually inactive males, 

 and in deep pigmentation in about 14 days. Daily drops of 5 to 10 /^g 

 of testosterone propionate applied directly to the beak produced 

 blackening of the fleshy rim of the nostril and angle of the mouth in 

 females in 3 to 5 days and a narrow black line on the adjacent horny 

 beak in 8 to 11 days. These results are completely in agreement with 

 those reported for the domestic sparrow (Pfeiffer et al, 1944) and 

 justify the use of beak pigmentation as a criterion for testicular ac- 

 tivity. 



