1306 



HORMONAL REGULATION OF BEHAVIOR 



with respect to shelters and nests does 

 change about the time of parturition. For 

 example, many female ungulates, which 

 normally live in herds on open range, leave 

 the herd and seek isolation and shelter at 

 the time of parturition {e.g., American elk, 

 Murie, 1951). The wood-mouse lives in a 

 hollow, globular nest of leaves and grass. A 

 male and female may both frequent the 

 same nest, but the female will usually force 

 the male to leave when the litter arrives 

 (Nicholson, 1941). Female domestic mice 

 observed in the laboratory can similarly 

 sometimes be seen, just after parturition, to 

 keep other animals out of a previously com- 

 mon nest (Leblond, 1940) . 



As the following data secured from labo- 

 ratory animals suggest, it may well be that 

 our failure more often to relate the nest- 

 building activity of wild mammals to the 

 reproductive cycle is partly a function of 

 the lack of quantitative data. 



The female domestic rabbit builds a nest 

 by piling up grasses, hay or straw, burrow- 

 ing into it, and hollowing it out. She then 

 plucks hair from the ventral surface of her 

 body and lines the nest with it. Sawin and 

 Crary (1953) reported that this nest-build- 

 ing activity takes place about the time of 

 parturition, just before or just after the ap- 

 pearance of the litter, depending on the 

 strain. The plucking of hair is associated 

 with a marked loosening of the hair on the 

 belly, dewlap, and thighs (Sawin and Crary, 

 1953; Klein, 1956). By weighing the amount 

 of hair obtained on different days by a 

 standard combing technique, it can be 

 shown that the loosening of the hair reaches 

 a peak during the 5 days before parturition 

 (Sawin, Denenberg, Ross, Hafter and Zar- 

 row, 1960). The pregnant African lioness 

 also pulls hair from her belly and around 

 her nipples just before parturition. In this 

 species, gestation lasts about 109 days, and 

 this type of hair-pulling is seen from about 

 100 days onward (Cooper, 1942). Loosening 

 of the hair in late pregnancy has also been 

 found in the Asiatic squirrel (Landry, 

 1959) . 



Similarly, nest-building behavior in the 

 domesticated rat is clearly related to the 

 endocrine condition of the animal. Kinder 

 (1927) measured the amount of nest-build- 

 ing in laboratory rats by counting the num- 



ber of strips of crepe paper used by them 

 for constructing the nest. She found that 

 males and nonpregnant females, on the av- 

 erage, perform the same amount of nest- 

 building activity per day. However, the 

 amount in the jemale is subject to a 5-day 

 cyclic variation, being minimum at estrus, 

 and maximum midway between the two 

 estrous periods. 



Li pregnant females there is a sudden rise 

 in nest-building activity about 5 days pre- 

 partum, the nest-building continuing at a 

 high level during lactation. Preparturient 

 and lactating females spend almost all their 

 time in nest-building, except w^hen suckling 

 young or eating. Similar observations were 

 made by Sturman-Hulbe and Stone (1929), 

 and by Beach (1937). Obias (1957) com- 

 pared the nest-building behavior of rats 

 just before and just after parturition, and 

 reported that the amount of nest-building 

 increases at the time of parturition. 



Koller (1952, 1956) kept individual do- 

 mestic mice in cages 40 cm. square. Mice 

 kept under such conditions, and provided 

 with hay as building material, will build 

 a nest each night, which can be removed and 

 weighed the next morning. Koller observed 

 that immature mice (beginning 1 to 2 weeks 

 before maturity), adult males, and non- 

 pregnant females all built small nests which 

 he called "sleeping nests" iSchlafnester), 

 the amount of nesting material used per 

 night ranging from about 7 to about 11 gm. 

 Pregnant females, on the other hand, build 

 much larger nests, averaging 45 to 50 gm. 

 per night, starting quite abruptly on the 4th 

 to the 5th day of pregnancy, and therefore 

 about the time when the corpus luteum of 

 pregnancy becomes histologically demon- 

 strable. As in the rats studied by Kinder, 

 the building of these larger nests, which 

 Koller called "brood nests (Brutnester) , 

 continued during lactation. 



Pearson (1944) states that pregnant 

 shrews in captivity build nests no different 

 from those built by nonpregnant animals. 

 However, no quantitative data are given, 

 nor do we have sufficient information about 

 the breeding of these animals to judge the 

 adequacy of the laboratory conditions as a 

 setting for the natural behavior pattern. 



Hypophyseal hormones and nest-building 

 behavior. Richter and Eckert (1936) found 



