PARENTAL BEHAVIOR 



1347 



situation. Herter (1936, 1952 j tested the 

 temperature preferences of a number of 

 small mammals in a gradient in which they 

 could come to rest at any temperature in 

 a considerable range. He found that mice 

 and rats of different strains and species 

 have characteristically different tempera- 

 ture preferences, and that these preferences 

 are correlated with the thickness of the 

 skin (Herter, 1941) and with the density 

 of the hair, expressed in terms of number 

 of hairs per unit of area (Herter and 

 Sgonina, 1939) . When strains with different 

 temperature preferences are hybridized, 

 variations in the temperature preferences 

 of the offspring are correlated with varia- 

 tions in the density of their body-hair 

 (Herter and Sgonina,' 1939; Wolburg, 1952). 

 Hair growth is in part under hormonal con- 

 trol (Mohn, 1958; Rennels and Callahan, 

 1959), although different skin areas are 

 characterized by specific intrinsic growth 

 properties of the hair and different areas of 

 the body may thus respond differently to 

 the same hormonal conditions (Whiteley, 

 1958). Hair growth in the domestic mouse 

 is inhibited in late pregnancy (Danneel 

 and Kahlo, 1947; Nay and Fraser, 1955). 

 Progesterone inhibits hair growth in male 

 mice (Danneel and Kahlo, 1947), although 

 it does not seem to do so in rats (Yazaki, 

 1956; Mohn, 1958). We may recall that 

 nest-building behavior in mice occurs ear- 

 lier in pregnancy (KoUer, 1952) than it 

 does in rats (Wiesner and Sheard, 1933), 

 and that progesterone induces nest-build- 

 ing behavior in mice (Roller, 1952). 



It is clear that at least some of the effects 

 of pituitary hormones on nest-building be- 

 havior in mammals may be due to altera- 

 tions in thermoregulatory mechanisms. 

 This, of course, refers only to the regulat- 

 ing effect on the amount of nest-building 

 behavior, and does not necessarily imply 

 anything about the neural organization of 

 the behavior patterns themselves, which 

 is not illuminated by this type of work. 

 Further, we are not justified in assuming 

 that hormonal effects on thermoregulatory 

 processes do not include effects by way of 

 the central nervous system; we can merely 

 say that any such effects are probably not 

 specific to nest-building behavior. 



Some further -problems. We have already 

 remarked that the presence of incubation 

 patches is, in many species of birds, cor- 

 related with the occurrence of incubation 

 behavior (Tucker, 1943; Davis, 1945; Mew- 

 aldt, 1952; Parkes, 1953). Since the incuba- 

 tion patch is an area the increased vascu- 

 larity of which is undoubtedly related to 

 the transmission of heat to the egg, and 

 since variations in ambient temperature 

 (Nice and Thomas, 1948) and in egg tem- 

 perature (Baerends, 1959) affect the in- 

 tensity with which the birds sit on the eggs, 

 it may be suggested that a change in skin 

 temperature coinciding with the develop- 

 ment of the incubation patch, and the cool- 

 ing effect on it of sitting on the eggs, may be 

 factors in the motivation of incubation be- 

 havior. Prolactin, which contributes to the 

 maintenance of incubation behavior, raises 

 the body temperature of roosters from 2 to 

 4°F. (Nalbandov, 1953). The rectal tem- 

 peratures of incubating domestic fowl are 

 not higher than those of nonincubating 

 birds (Simpson, 1911), but Nalbandov 

 (1953) suggests that this is probably the 

 result of the lack of activity of incubating 

 birds. It is unlikely that aff'erent inflow 

 from the incubation patch is the most im- 

 portant source of motivation to incubate, 

 because some species of birds incubate with- 

 out possessing such patches. The contribu- 

 tion of such factors to the regulation of 

 incubation behavior should nevertheless be 

 further investigated. 



There are other examples of peripheral 

 effects of hormones on behavior, not related 

 to parental behavior, which I have dis- 

 cussed elsewhere (Lehrman, 1956b). We 

 may briefly cite one of them. Adult female 

 dogs squat to urinate ; adult males raise one 

 leg (Berg, 1944). Males castrated in in- 

 fancy do not raise their legs to urinate, but 

 will do so if injected with male hormone. 

 Female puppies and spayed female dogs 

 also show the male micturition pattern if 

 injected with male hormone (Martins and 

 Valle, 1948). Freud and Uyldert (1948b) 

 showed that local anesthesia of the olfactory 

 epithelium caused the disappearance of the 

 male micturition pattern and its replace- 

 ment by the female pattern. When the anes- 

 thesia wore off, the male pattern reappeared. 



