1292 



HORMONAL REGULATION OF BEHAVIOR 



eggs) , whereas in the male satin bower-bird, 

 which does not incubate or feed the young, 

 this change in the testis is delayed several 

 weeks, until the end of the breeding season. 

 Collias (1940) found that the injection of 

 1 to 5 mg. per day of testosterone propio- 

 nate into incubating hens caused the birds 

 to desert their eggs within 3 to 13 days 

 after the first injection. Kosin (1948) ad- 

 ministered 10-mg. doses of testosterone pro- 

 pionate by injection into laying turkey hens 

 at 2-week intervals, and found that this 

 treatment prevented the onset of broodiness. 

 On the other hand, male pigeons which nor- 

 mally take part in incubation are not pre- 

 vented from incubating by testosterone pro- 

 pionate administration, nor do male pigeons 

 discontinue established incubation when in- 

 jected with as much as 2 mg. testosterone 

 propionate daily (Collias, 1940, 1950, 1952). 

 In the case of the black-crowned night 

 heron, another species in which the male and 

 female appear externally identical, and in 

 which the male and female share the duties 

 of incubation, Noble and Wurm (1940) 

 found that testosterone propionate induced 

 incubation behavior when injected into fe- 

 males or males. Riddle and Lahr (1944) 

 similarly report that testosterone propio- 

 nate, implanted into female ring doves, in- 

 duced incubation in about 50 per cent of the 

 birds. In unpublished experiments, I have 

 failed to verify this observation. A consid- 

 eration of the conditions of our experiments 

 and of those of Riddle and Lahr and of 

 Noble and Wurm may reveal a possible 

 cause for the difference in results. The ring 

 doves tested by Riddle and Lahr, and the 

 black-crowned night herons tested by Noble 

 and Wurm, were kept in pairs in the cage 

 during the period of hormone administra- 

 tion. In the case of Riddle and Lahr's ring 

 doves, the tests were performed with uni- 

 sexual pairs of females. Our experiments, on 

 the other hand, were done by injecting the 

 hormone into the experimental birds during 

 a 1-week period when each bird was alone 

 in an isolation cage. At the end of the treat- 

 ment period, the birds were placed in pairs 

 in cages containing a nest and eggs. Under 

 these conditions, birds treated with testos- 

 terone propionate failed to sit on the eggs, 

 although other hormone treatments did in- 



duce incubation behavior (see below). I 

 suggest the possibility that the testosterone 

 propionate treatments, in Riddle and Lahr's 

 experiment, actually induced male court- 

 ship behavior, which in those pairs in which 

 the level of response was very different as 

 between one bird and the other, would re- 

 sult in a faster formation of the pair than 

 with untreated pairs of females, and that 

 this courtship behavior, leading to pair for- 

 mation, stimulated the secretion of endoge- 

 nous hormones which in turn were responsi- 

 ble for the incubation behavior. When the 

 birds were kept in isolation during the 

 treatment period, the behavioral effects of 

 the male hormone injection could have no 

 stinuilating effect on the other bird (see be- 

 low). 



(3) Estrogens. Estrogens injected into 

 laying or nonlaying hens failed to induce 

 incubation behavior (Riddle, 1937; Nal- 

 bandov, 1945) , and FSH also was ineffective 

 (Riddle, Bates and Lahr, 1935). The re- 

 sults from a number of studies have shown 

 that estrogens administered to incubating 

 domestic hens will cause them to discon- 

 tinue sitting on the eggs. The most sys- 

 tematic of these was that by Godfrey and 

 .Taap (1950) who injected each of 37 sitting 

 hens with 15 mg. diethylstilbestrol. Twenty- 

 eight of the 37 had left the nest by the 4th 

 or 5th day after the treatment. The birds 

 had been sitting from 3 to 7 days at the 

 time of the treatment. Although no un- 

 treated controls were used, it is clear that 

 the treatment with diethylstilbestrol inter- 

 rupted the incubation behavior, which nor- 

 mally lasts much longer than the 12-day 

 maximum found in the responding birds. 

 When the dosage was increased to 30 mg., 

 100 of 102 treated birds discontinued sitting. 

 Among the 11 birds in the 15-mg. group in 

 which incubation was not interrupted by 

 diethylstilbestrol treatment, 5 left the nest 

 during the 2nd day after injection and re- 

 turned the following day. In 10 of the 11 

 incubation was discontinued as a result of a 

 2nd injection. This effect of exogenous es- 

 trogen has been verified for the domestic 

 hen (Collias, 1940; Carson, Eaton and Ba- 

 con, 1956) and turkey (Blakely, Anderson 

 and MacGregor, 1951). On the other hand, 

 van Tienhoven (1958) reported that di- 



