PARENTAL BEHAVIOR 



1291 



8it on eggs as a result of prolactin injection. 

 These experiments with ring doves and with 

 canaries were carried out with nonlaying 

 birds and are being continued. 



Attempts to induce incubation behavior 

 by prolactin injection in male birds of spe- 

 cies in which the male does not normally sit 

 have not been successful. When roosters or 

 capons are injected with prolactin, and then 

 offered eggs, they do not sit, although, in 

 most cases, they utter the clucking sounds 

 characteristic of a hen in the process of be- 

 coming broody (Riddle, Bates, and Lahr, 

 1935;-Eigemann, 1937; Nalbandov, 1945; 

 Nalbandov and Card, 1945; Saeki and 

 Tanabe, 1955). 



The fact that male domestic chickens do 

 not incubate in response to prolactin in- 

 jection, in distinction to laying hens, does 

 not necessarily indicate that males and fe- 

 males differ in their capability of incubat- 

 ing, given the proper hormonal situation. 

 We will recall that nonlaying hens do not 

 incubate when injected with prolactin. Pre- 

 sumably the effect of prolactin in inducing 

 incubation in laying hens depends on prim- 

 ing by ovarian hormones, or on recent at- 

 tachment to the egg-laying place, or on 

 some combination of these. It may well be 

 that when these factors have been analyzed, 

 they will be found to apply to males as well 

 as to nonlaying females. 



(3) Other pituitary hormones do not 

 seem to induce incubation behavior. This 

 includes follicle - stimulating hormone 

 (FSH). luteinizing hormone (LHl, and 

 thyrotrophic hormone (TSHi (Riddle, 

 Bates and Lahr, 1935; Riddle, 1937). 



(41 The antigonad effect of prolactin 

 may be considered relevant to its efficacy 

 in imlucing incubation behavior, because the 

 suppression of the secretion of gonadal hor- 

 mones implies a reduction in gonad-stimu- 

 lated sexual behavior, which might inter- 

 fere with the onset of parental behavior 

 (Lehrman, 1955). Bates, Lahr and Riddle 

 (1935) found that injections of prolactin 

 were followed by sharp decreases in the 

 weight of the ovaries and oviducts, which 

 did not occur when FSH was injected with 

 the prolactin (Bates, Riddle and Lahr, 

 1937 ) . This implies that the antigonad ac- 

 tion of prolactin is by way of the suppres- 



sion of the secretion of gonad-stimulating 

 hormones by the pituitary glands. Similar 

 effects were found in male domestic chick- 

 ens (Nalbandov, 1945; Yamashina, 1952). 

 In wild birds prolactin injections can pre- 

 vent the normal increase in gonad weight 

 caused by increasing light (Bailey, 1950). 

 Prolactin injected during the breeding sea- 

 son is followed by the collapse of the testes 

 and by the lipid metamorphosis (steato- 

 genesis) of the tubules, which normally oc- 

 cur at the end of the breeding season 

 (Coombs and Marshall, 1956; Lofts and 

 Marshall, 1956j . 



Gonadal hormones and incubation be- 

 havior. (1) Testosterone. The occurrence oi 

 endogenous prolactin during incubation, the 

 antigonad effect of prolactin, the effective- 

 ness of prolactin in inducing incubation be- 

 havior, and the lack of sexual behavior dur- 

 ing periods of incubation all suggest that 

 the gonadal hormones responsible for sexual 

 behavior and nest-building may be incom- 

 patible with the performance of incubation 

 behavior, and experimental data in general 

 support this impression. 



Champy and Colle (1919) reported that 

 the development of the crop-sac in incubat- 

 ing pigeons was accompanied in the male by 

 a 90 per cent decrease in testis volume, and 

 in the female by atresia of the ovarian fol- 

 licles. In the domestic hen broody clucking 

 occurs at a time when no eggs are being 

 laid, comb size is minimal, and no copula- 

 tions are taking place (Collias, 1950). In 

 the wild bank swallow the beginning of in- 

 cubation is accompanied by a sharp drop in 

 the weight of the ovary (from about 300 

 mg. to about 53 mg.) and of the oviduct 

 (from about 1500 mg. to about 200 mg.) 

 ( Petersen, 1955 ) . Testis weights, which have 

 increased during nest-building and egg-lay- 

 ing, remain high during incubation. Note 

 that in this species the male develops no 

 brood patch and does almost no incubation, 

 unlike the situation in pigeons and doves in 

 which the male participates in the care of 

 the eggs. Marshall and Serventy (1956) 

 found that the testis of the male short- 

 tailed shearwater collapses very quickly 

 after mating, coincident with the onset of 

 his incubation duties (male and female 

 shearwaters take turns in incubating the 



