PARENTAL BEHAVIOR 



1307 



that hypophyscctomy greatly increases the 

 amount of nest-building activity in rats. 

 The 12 animals used in their principal ex- 

 l)erimcnt performed about 178 per cent more 

 ne^t-building behavior (measured by the 

 amount of paper used) after removal of the 

 pituitary gland than before. After more ex- 

 tensive later experiments, Richter (1937) 

 reported that many rats did five times as 

 much nest-building after hypophysectomy 

 as before. These experiments were done with 

 nonpregnant animals, and the amount of 

 nest-building behavior reported after hy- 

 pophysectomy is comparable with the maxi- 

 mal amount normally seen in pregnant ani- 

 mals. Similar results were obtained by Stone 

 and his co-workers (Stone and King, 1954; 

 Stone and Mason, 1955) who rated the nests 

 built by intact 60-day-old male albino rats, 

 and compared them with the nests built by 

 rats of the same age which had been hy- 

 pophysectomized at 35 days of age. These 

 ratings were based, not only on the amount 

 of nesting material used, but also on the type 

 of construction, higher ratings being given 

 to nests which, from the point of view of 

 compactness, cover, etc., appeared to be 

 better insulating or heat-conserving devices. 

 When rated in this way hypophysectomized 

 animals were judged to have built "better" 

 nests. In their original paper, Richter and 

 Eckert had noted that normal nonpregnant 

 rats built loose and shapeless nests, whereas 

 hypophysectomized animals constructed 

 woven balls with single small openings to 

 an inner chamber. 



An apparent contradiction to the general 

 agreement that hypophysectomy increases 

 both the quantity and the quality of nest- 

 building in domestic rats appears in the 

 study of Obias (1957j, who hypophysecto- 

 mized pregnant rats on the 13th day of ges- 

 tation. Of his 11 experimental animals, 5 

 died at parturition. Obias rated the nests 

 built by the hypophysectomized animals 

 and by intact controls during the 10 days 

 before parturition, and the nests built by 

 the surviving hypophysectomites and by 

 the controls during the 10 days after par- 

 turition, and found no differences between 

 the intact and the hypophysectomized ani- 

 mals. The failure of hypophysectomy to af- 

 fect the nature of the nest in pregnant rats, 

 in contrast to the striking effect of this op- 



eration in non-pregnant animals, is pre- 

 sumably due to the fact that placental hor- 

 mones can have the same effect as the rele- 

 vant pituitary hormones. 



Information about the effect of exogenous 

 pituitary or pituitary-like hormones on 

 nest-building activity is scanty. Tietz 

 (1933) injected pregnancy urine into 14 

 nonpregnant female rabbits, and found that 

 50 per cent of them built nests, using in part 

 hair which had become loosened as a result 

 of the treatment and which the rabbits 

 pulled out from their bodies. Inspection of 

 the ovaries of these animals through ex- 

 ploratory laparotomies showed that some 

 of the treated rabbits developed corpora 

 lutea, and that the fur became loosened only 

 in those animals in which the corpora lutea 

 developed. 



Prolactin did not induce nest-building be- 

 havior in either male or female domestic 

 mice (Roller, 1952). 



Oddly enough, investigators interested in 

 this subject do not seem to have injected 

 pituitary extracts into hypophysectomized 

 rats, in order to see which pituitary frac- 

 tions would prevent the increase in nest- 

 building activity after hypophysectomy. 

 However, as will be seen from the next sec- 

 tion, data on the effects of nonpituitary 

 hormones on nest-building permit a rea- 

 sonably good guess as to the nature of the 

 effects of hypophysectomy. 



Gonadal and thyroid hormones and nest- 

 biiilding behavior. Removal of the thyroid 

 glands in rats induces a rise in the quantity 

 of nest-building behavior of the same order 

 as that induced by hypophysectomy (Rich- 

 ter and Eckert, 1936; Richter, 1937, 1941). 

 Further, thyroid extract administered to 

 intact rats is capable of inhibiting their 

 nest-building behavior (Richter, 1943). 

 Richter suggests that the enhanced nest- 

 building activity resulting from hypophy- 

 sectomy is due to the loss of thyroid func- 

 tion, a point which we shall discuss in more 

 detail elsewhere (p. 1346). 



The effect of thyroidectomy in the rabbit 

 appears to be different from that in the rat, 

 although data in exactly comparable situa- 

 tions are not available. Chu (1945) removed 

 the thyroid glands from female rabbits 

 which were then allowed to become preg- 

 nant from 17 to 108 days later. These ani- 



