1304 



HORMONAL REGULATION OF BEHAVIOR 



companied by the same hormonal changes. 

 It is probable that brooding of the young 

 (providing heat) has more in common with 

 incubation behavior than do other aspects 

 of parental care (feeding the young, lead- 

 ing them, protecting them, allowing them to 

 huddle under the wing, etc.), but informa- 

 tion which might clarify this point is still 

 inadequate. 



Nalbandov (1945) suggested that pro- 

 lactin induces "broodiness" largely or solely 

 through its antigonad (or, more properly, 

 antigonadotrophic) effect. It should be 

 pointed out, however, that hypophysectomy 

 interrupts incubation behavior of sitting 

 hens within 23 hours (Prohaszka, quoted 

 by Saeki and Tanabe, 1955) thus indicating 

 that the maintenance of incubation behavior 

 does not depend merely on the removal of 

 pituitary gonadotrophins. On the other 

 hand, castration alone makes male domestic 

 chickens capable of being rendered broody 

 by confinement with chicks, and this effect 

 is not accompanied by increased prolactin 

 secretion. Note also that prolactin induces 

 incubation behavior in hens only if they were 

 laying at the time of treatment, and that it 

 does not induce incubation behavior at all 

 in males, whereas care of the young is in- 

 duced by prolactin alone. These data sug- 

 gest that incubation behavior may be in- 

 duced by some positive action of prolactin 

 on a tissue previously primed by ovarian 

 hormones, whereas broody care of the young 

 may be facilitated merely by the antigonad 

 action of prolactin. 



In any event it now seems desirable to 

 distinguish sharply between behavior to- 

 ward the eggs (incubation behavior) and 

 behavior toward the young (brooding and 

 parental care) . Our knowledge of these mat- 

 ters has now reached the point where the 

 use of the general term "broodiness" to 

 cover all aspects of parental behavior to- 

 ward the eggs and young may be mislead- 

 ing.^ 



^ A number of additional references to work on 

 hormonal regulation of behavior in birds may be 

 found in the review by Eisner (1960), which ap- 

 peared too late to be considered in the prepara- 

 tion of this chapter. 



III. Hormones and Parental Behavior 

 in Infrahunian Mammals 



The reader will soon become aware of a 

 rather unfortunate difference between our 

 material relating to birds and that relating 

 to mammals. Several rich sources of infor- 

 mation with respect to parental behavior 

 and its physiologic bases, on which we have 

 drawn in our discussion of birds, simply do 

 not exist for mammals, or, if so, only to a 

 very restricted degree. The relationship be- 

 tween egg production and broodiness in do- 

 mestic hens has stimulated a good deal of 

 research on these problems in an agricul- 

 tural setting, of which we have taken ad- 

 vantage. Farm mammals do not seem to 

 have stimulated interest in the same type of 

 problem except for the case of the control of 

 lactation. Another striking difference be- 

 tween the available information on birds 

 and that on mammals stems from the ex- 

 istence of a large and enthusiastic supply 

 of amateur, semiprofessional, and profes- 

 sional bird-watchers whose contributions 

 range from systematic descriptive accounts 

 of the behavior of various species of birds 

 through a variety of more or less casual 

 experiments which, although usually rather 

 anecdotal, are often extremely suggestive, 

 to excellent experimental studies carried 

 out in the field on relatively undisturbed 

 free-living birds. The natural history of 

 mammals simply has not excited nearly so 

 widespread or so intense an interest in such 

 a variety of people (including the present 

 author). In addition, the places in which 

 most mammals rear their young are very 

 much less accessible than is usually the 

 case with birds, so that opportunities for 

 observation are much more sharply re- 

 stricted. There are, of course, notable ex- 

 ceptions, such as Darling's (1956) classic 

 field study of the Scottish red deer, Hedi- 

 ger's (1950) interesting and fruitful studies 

 of the behavior of mammals in zoos, Eibl- 

 Eibesfeldt's (1958) remarkably detailed 

 studies of the behavior of a variety of mam- 

 mals under simulated natural conditions in 

 a research institute, and a number of others. 



Another difference between our treatment 

 of birds and of mammals depends on the 

 fact that the relationship between ovula- 



