PARENTAL BEHAVIOR 



1303 



Allen and Nice, 1952 ; Whitehouse and Arm- 

 strong, 1953). However, the assumption 

 that the physiologic bases of incubation and 

 of brooding are somewhat different is sup- 

 ported by the fact that, in some species in 

 which both sexes share in incubation and 

 in brooding, the relative share of the sexes 

 in these two behaviors is quite different. 

 For example, although male and female 

 pied-billed grebes both incubate the eggs, 

 the female does most of the brooding of the 

 newly hatched young (Deusing, 1939). In 

 the bank swallow, in which the female does 

 most of the incubating, the male and the 

 female may share more nearly equally in 

 the brooding of the young, although there 

 are no data which indicate whether the male 

 actually provides heat to the young (Peter- 

 sen, 19551 . 



Experimental induction of incubation be- 

 havior and of broody behavior. The most 

 striking evidence for the distinctness of in- 

 cubation behavior and of broody care of the 

 young comes from the work of Nalbandov 

 (Nalbandov, 1945; Nalbandov and Card, 

 1945) who found that prolactin would not 

 induce domestic cocks to sit on eggs, re- 

 gardless of dosage, but that this hormone 

 induces cocks to adopt chicks, to protect 

 them under their body and wing, to lead 

 them to feed and water, to cluck to them, 

 to protect them against intruders, etc. Fur- 

 ther, confining cocks with eggs did not in- 

 duce them to incubate, although confining 

 them with chicks effectively caused them to 

 become broody and to care for the chicks. 

 Schjelderup-Ebbe (1924) noted great indi- 

 vidual differences among domestic hens with 

 respect to the efficiency and intensity of 

 their broody care of chicks. Some hens 

 which incubated eggs very devotedly until 

 hatching showed no interest whatever in the 

 chicks after hatching. Lashley (1915) found 

 that sooty terns who were sitting on eggs 

 less than 2 weeks old would not adopt young 

 chicks. A colony of emperor penguins al- 

 ways includes some nonincubating birds. 

 When the eggs hatch, these birds suddenly 

 become very aggressive and try to get the 

 young. The actual parents sometimes give 

 up the young to such other birds, which then 

 feed the chicks by regurgitation. Further, 

 birds which have played no role in incu- 

 bating the eggs, and which have been feed- 



ing at sea for some weeks or months during 

 the incubation period, may feed the young 

 birds by regurgitation immediately after 

 their arrival in the colony at the end of the 

 incubation period, indicating that the abil- 

 ity to feed the young by regurgitation is not 

 continuous with or conditioned by incuba- 

 tion (Prevost, 1953; Stonehouse, 1953). 

 There are other cases, however, in which 

 behavior toward the eggs and the young 

 may be more or less interchangeable. Allen 

 and Mangels (1940) exchanged eggs and 

 young (age not reported) between different 

 pairs of black-crowned night herons and 

 found that the new contents of the nest were 

 accepted and brooded by both groups of 

 parents, although the sudden appearance of 

 young caused considerable disturbance to 

 the parents. Emlen (1941) similarly found 

 that young tricolored redwinged blackbirds 

 introduced into nests in which the incuba- 

 tion of eggs had just begun would readily be 

 accepted and fed. 



Hormonal concomitants of incubation 

 and of broodiness. Another indication that 

 the physiologic bases of incubation and 

 broodiness are different may be found in the 

 fact that normally occurring incubation be- 

 havior is associated with a high level of 

 prolactin in the pituitary gland, whereas 

 broody care of the young is not (see above) . 

 Further, when broody behavior is induced 

 by keeping hens, capons, or cocks with 

 young birds, no increase in prolactin con- 

 tent of the pituitary gland accompanies 

 the onset of this broodiness (Saeki and 

 Tanabe, 1955) in contrast to the situation 

 when incubation is extended by the presence 

 of eggs. Finally, Ramsay (1953) reports 

 that broodiness induced by confinement 

 with young is not associated with the for- 

 mation of the incubation patch which occurs 

 along with normal broodiness. 



Conclusion. Although many more data are 

 obviously needed on the whole range of 

 problems connected with the hormonal basis 

 of inculcation and broodiness, it is reason- 

 ably clear that incubation behavior, on the 

 one hand, and parental care of the young, 

 on the other, are not identical tendencies. 

 They are differently distributed in the natu- 

 ral history of birds, they are not induced in 

 the same way by external stimuli or by 

 hormone treatment, and they are not ac- 



