1300 



HORMONAL REGULATION OF BEHAVIOR 



lactin, and then placed in the cages with the 

 squabs, 10 out of 12 fed the squabs by re- 

 gurgitating the crop-milk which had been 

 formed under the influence of the exogenous 

 prolactin (Beams and Meyer, 1931 ; Riddle 

 and Bates, 1939) . When birds were similarly 

 injected with prolactin but their crops were 

 anesthetized by the injection of a long-act- 

 ing local anesthetic into the crop wall or into 

 the skin over the crop, a significant number 

 of birds failed to feed the squabs, compared 

 with control birds in which the anesthetic 

 was injected elsewhere than in the crop. I 

 concluded that the ability of prolactin to 

 elicit the regurgitation-feeding behavior of 

 these birds toward the young depended on 

 stimulation arising in the crop as a result of 

 its engorgement by the action of prolactin 

 (and on the antigonad action of prolactin, 

 which prevented sexual or aggressive behav- 

 ior from interfering with parental behavior 

 toward the squabs) . Although I believe that 

 this was probably correct, there are situa- 

 tions in which doves regurgitate when the 

 crop is not engorged, and when there may 

 be little or no prolactin present. The amount 

 of crop-milk produced by parent pigeons 

 decreases starting 2 or 3 days after the 

 hatching of the young; after the young are 

 7 or 8 days old, the regurgitated crop con- 

 tents consist entirely of grain, indicating 

 that no crop-milk is being produced (Patel, 

 1936). Schooley and Riddle (1938) found 

 that the amount of prolactin in the pitui- 

 tary glands of pigeons with 7 to 15 day old 

 young was considerably lower (1.05 of their 

 units) than in the pituitarics of incubating 

 birds (2.50 units), although it was not as 

 low as in the pituitaries of sexually active 

 birds (0.14 units). There are no data avail- 

 able to indicate whether this low level of 

 prolactin (too low to cause the formation 

 of crop-milk), may nevertheless stimulate 

 regurgitation - feeding of ingested grain. 

 When male pigeons are castrated they may 

 still be able to induce the laying of eggs by 

 females with which they were already 

 mated, and they will sit on eggs and show 

 crop development and crop-milk production 

 during the first incubation period after cas- 

 tration (Kaufman and Dobrowska, 1931 ; 

 Kaufman, 1932; Patel, 1936). During sub- 

 sequent incubation periods, however, there 



will be no crop development, although the 

 birds may incubate. Since castration does 

 not affect the sensitivity of the crop to pro- 

 lactin (Riddle and Dykshorn, 1932), the 

 effect of castration in preventing crop de- 

 velopment during subsequent incubation pe- 

 riods is presumably due to a failure of pro- 

 lactin secretion by the pituitary. It may be 

 noted that the acidophilic cells which are 

 associated with the periods when prolactin 

 is being secreted (Schooley, 1937; Payne, 

 1943; Yasuda, 1953), gradually disappear 

 from the pituitary glands of pigeons during 

 the 2 or 3 months following castration 

 (Schooley, 1937) . Kaufman (1932) reported 

 that one such castrated male, after having 

 taken part in incubation, fed the young with 

 grain, although no crop development took 

 place. The role of the condition of the crop 

 in the occurrence of this regurgitation-feed- 

 ing behavior obviously needs further in- 

 vestigation. 



Gonadal hormones and the brooding of 

 young. It is well known that androgenic hor- 

 mones inhibit the brooding of the young. As 

 long ago as 1916, Goodale observed that 

 capons become broody when kept with 

 chicks, and care for them in normal hen- 

 fashion (Goodale, 1916, 1918). Saeki and 

 Tanabe (1955) have confirmed this obser- 

 vation. Collias (1940) injected 4 mg. tes- 

 tosterone propionate per day into a hen with 

 chicks, and found that she stopped clucking 

 and caring for the chicks after 5 days. Nal- 

 bandov (1945) found that the injection of 

 FSH or of 0.1 mg. methyltestosterone per 

 day along with prolactin prevented broodi- 

 ness from developing in response to the pro- 

 lactin. Estradiol benzoate has an effect 

 similar to that of testosterone in interrupt- 

 ing broody care of the young (Collias, 

 1940 1 . 



3. Induction of Parental Behavior toward 

 Young by External Stimuli 



Changes in behavior of the parents at 

 hatching. We have already pointed out that 

 incubation behavior, and the associated 

 prolactin secretion, can be maintained for 

 abnormally long periods of time by stimuli 

 coming from the eggs. This implies of course 

 that changes in the behavioral and/or phys- 

 iologic condition of the parent are stimu- 



