1290 



HORMONAL REGULATION OF BEHAVIOR 



measured the prolactin content of the pi- 

 tuitary gland of laying hens in their sec- 

 ond laying year, which had been judged 

 genetically broody or nonbroody on the 

 basis of whether they became broody during 

 their first laying year. They found twice as 

 much prolactin in the pituitary glands of 

 the broody type as in those of the non- 

 broody type. 



The growth of the crop of pigeons and 

 doves during the incubation period is, of 

 course, a priori evidence of increased pro- 

 lactin production. Schooley and Riddle 

 (1938) assayed the prolactin content of 

 the pituitary glands of pigeons, their unit 

 being the increase in crop weight of the host 

 pigeon per milligram of implanted pituitary 

 tissue. They found sexually active adult 

 birds to have 0.14 units of prolactin per 

 pituitary gland, whereas birds in midincu- 

 bation had 2.50 units. Lahr and Riddle 

 (1938) found a much higher rate of mitosis 

 in the crop epithelium of incubating and of 

 prolactin-injected pigeons than in that of 

 nonincubating pigeons. The pituitary glands 

 of female pigeons contain more prolactin 

 than those of male pigeons (Hurst, Meites 

 and Turner, 1943; Meites and Turner, 

 1947). Male and female doves both incu- 

 bate, but the female spends three times as 

 much time on the eggs as the male (Whit- 

 man, 1919). 



Bailey (1952) assayed the prolactin con- 

 tent of the pituitary glands of California 

 gulls by implanting them over the crops of 

 domestic pigeons. He found that gulls which 

 had brood patches when they were collected 

 (both males and females) had more pro- 

 lactin in their pituitary glands than those 

 with no incubation patches. 



A further indication of the occurrence of 

 prolactin during incubation in birds other 

 than domestic pigeons and chickens is pro- 

 vided by the fact that molting stops during 

 incubation in canaries (as in other birds), 

 and that prolactin inhibits molting when in- 

 jected during other times of the reproduc- 

 tive cycle (Kobayashi, 1953b). 



(2) Injection of prolactin induces incu- 

 bation behavior in laying domestic hens of 

 broody strains. Riddle, Bates and Lahr 

 (1935) injected prolactin daily into 20 lay- 

 ing hens of broody races. Although clucking 



followed by incubation behavior normally 

 occurs only at or near the end of the egg- 

 laying period, all 20 began clucking within 

 2 to 4 days after the beginning of the injec- 

 tion, except for one bird which clucked on 

 the 1st day, and 1 which did not begin 

 until the 7th day. Sixteen of the 20 birds 

 began sitting on eggs within less than 3 days 

 after the beginning of clucking. When 10 

 laying hens of a nonbroody race (white 

 Leghorn) were treated in the same way, 7 of 

 the birds began clucking after 3 to 5 days, 

 but only 1 of the 7 incubated on the follow- 

 ing day. (Note that up to 15 per cent of 

 broody hens are found in populations of 

 ''nonbroody" races.) When prolactin was in- 

 jected into nonlaying hens, most began 

 clucking after a few days, but none was in- 

 duced to incubate. The efficacy of prolactin 

 in inducing incubation behavior in the do- 

 mestic hen has been verified by other in- 

 vestigators (Eigemann, 1937; Riddle, 1937; 

 Nalbandov and Card, 1945; Saeki and Ta- 

 nabe, 1955). 



^Ir. Philijj Brody and I have tested ring 

 doves iin which both sexes normally incu- 

 bate) for incubation behavior after injec- 

 tion of various amounts of prolactin. If each 

 bird is injected over a 7-day period with a 

 total of approximately 400 I.U. of prolactin, 

 and the birds are then tested for their re- 

 sponse to eggs in individual pairs, each in 

 a single test cage, incubation behavior is 

 seen in approximately 40 per cent of the 

 pairs. In these birds, maximal crop-growth 

 has occurred in response to the prolactin 

 injections (increase in crop weight from ca. 

 900 mg. to ca. 3000 mg.). When the total 

 amount of prolactin is reduced to 50 I.U., 

 the number of birds in which incubation 

 behavior is induced drops to about 20 per 

 cent. Even with this dosage, however, the 

 lowest we have yet tried, there is a 60 per 

 cent increase in crop weight. Since, in a nor- 

 mal cycle, the birds begin to sit on the eggs 

 some days hejore there has been any de- 

 tectable increase in crop weight, these data 

 do not indicate that prolactin plays a role 

 in the onset of incubation behavior in this 

 species. Dr. R. A. Hinde of Cambridge Uni- 

 versity informs me that, in experiments 

 carried out with Dr. R. P. Warren, he 

 failed to induce canaries of either sex to 



