REPRODUCTIVE ENDOCRINOLOGY IN BIRDS 



1091 



were very much enlarged, but Leroy (1958) 

 was also able to obtain these large combs by 

 enclosing the comb in a cloth cover which 

 would interfere with heat dissipation from 

 the comb surface; this suggests that tem- 

 perature may have been an important fac- 

 tor in his experiments. 



Attempts have been made to use the size 

 of the comb or the rate of comb growth 

 within a breed of chickens as an aid in se- 

 lection of more fertile or of genetically 

 superior males. Although the lines produc- 

 ing fertile males earlier can be selected 

 successfully by choosing the cockerels with 

 the larger combs, no selection can be made 

 in this manner for superior subsequent fer- 

 tility (Parker, 1956). Goodwin, Cole, Hutt 

 and Rasmusen (1955) found that their 

 strain with larger combs, larger testes, and 

 earlier spermatogenic activity was also the 

 strain with the lower fertility. The lower 

 fertility was not caused by the interference 

 of the large comb with mating activity, for 

 all males were dubbed at 9 weeks of age. 



Pasvogel (1952) tested the hypothesis 

 that comb growth of cockerels might aid 

 in predicting the egg-laying performance 

 of their offspring. In 3 out of 4 trials a 

 selection of males on the basis of their 

 comb growth resulted in higher egg produc- 

 tion of the next generation. Unfortunately, 

 this hypothesis has not been confirmed by 

 more extensive tests. 



As might be expected, androgens play an 

 important role in the regulation of the ac- 

 tivity and size of the secondary sex organs ; 

 the seminal vesicles in a number of pas- 

 serine birds (Wolfson, 1954a), the vas 

 deferens in the starling <Witschi and Fugo, 

 1940), the cloacal gland of Coturnix c. ja- 

 ponica (Nagra, Meyer and Bilstad, 1959), 

 the phallus of the fowl (Nishiyama, 1954), 

 and the penis of the drake and gander. The 

 synchronization of spermatogenic activity 

 and the activity of these secondary sex or- 

 gans, in birds as in mammals, involves the 

 regulation of spermatogenic activity di- 

 rectly by the pituitary and of the secondary 

 sex organs by androgens, which in turn are 

 under the control of pituitary secretions. 

 This synchronization fits well into the hy- 

 pothesis that the gonadotrophic complex 

 is secreted and released as one complex, as 



has been proposed from different lines of 

 evidence by Nalbandov (1959a) and van 

 Tienhoven (1959). 



Other developments influenced by andro- 

 gen secretion which do not seem to be di- 

 rectly involved in reproduction are: the 

 normal development of the uropygial gland 

 (Kar, 1947a), regression of the Bursa 

 fabricii (Glick, 1957) , the head furnishings 

 of the turkey (Herrick, 1951), and in- 

 creased resistance to lymphomatosis (Bur- 

 mester and Nelson, 1945) . Beak color, which 

 may play a role in species recognition and 

 mate selection, is regulated by androgen 

 secretion in some species. Examples are: 

 the black bills of the sparrow, Passer 

 domesticus, African weaver finches, Eu- 

 plectes orix, and the indigo bunting, Pas- 

 serina cyanea; also the yellow bill of the 

 starling, Sturnus vulgaris, and the crimson 

 bill of the blackheaded gull, Larus ridi- 

 bundus (Benoit, 1950a; Dorfman and Ship- 

 ley, 1956). 



In studies of blood chemistry of chickens, 

 Sturkie (1955) obtained a decrease in the 

 blood sugar after androgen administration. 

 However, on reinvestigation of this problem 

 Tapper and Kare (1956) found that al- 

 though the glucose content per volume of 

 blood was decreased, the glucose content 

 l^er volume of serum was not affected. These 

 investigations established the fact that the 

 change in blood glucose was caused by an 

 increase in the number of red blood cells. 

 In view of this increase it is not surprising 

 that Tanaka and Rosenberg (1955) found 

 an increased hemoglobin content as a result 

 of androgen administration to capons. In 

 roosters, however, the differences were not 

 always significant. 



Some external characters, such as de- 

 velopment of spurs and sexual dimorphism 

 of jilumage color, characters which at first 

 sight might be suspected of being under the 

 influence of androgen secretions, are not the 

 result of the presence of androgen but rather 

 of the absence of estrogen. For instance, 

 castration of the mallard duck, Anas 

 platyrhijnchos, results in the colorful drake 

 feather pattern (Benoit, 1950a). An ex- 

 ception to the above generalization are cer- 

 tain feathers of the ruff, Philomachus 

 puguax. The development of spurs has been 



