IRENAUS ElBL-EIBESFELDT 57 



screen. Among these were animals who tended to sleep in another corner 

 of the cage. An unlearned preference for the most covered place prevailed 

 in these cases over the effects of previous experience. Three of the experi- 

 mental animals started behind the screen within i hour. Nine decided, 

 within 5 hours, to build in another corner. To sum up: of the eighty-two 

 virgin females, seventy-six built a nest, forty-four of these within the fnst 

 hour of the test, and only six rats did not build. 



In all animals that showed an interest in the nesting material, the above 

 mentioned movements of nest building were observed. Most of the 

 animals explored the rack and the paper at their first encounter by nibbling 

 and sniffing. Then they tore one or a few strips out of the rack and carried 

 them without much hesitation to the prospective nesting site. There they 

 deposited the nesting material, and often nest-building movements like 

 splitting, scratching and pushing appeared, although of no use at this 

 stage. These movements usually lasted for only a few seconds before they 

 started for more paper. From the behaviour of the animal one did not get 

 the impression that they had any idea what the result of their behaviour 

 would be. The behaviour released by the nesting material consisted simply 

 of certain building movements, in disorderly sequence. But, in all cases, 

 a nest was the result of the rat's activity. In five cases the experimental 

 animals were given pieces of straw instead of paper. These, too, started to 

 build, and all started to split the straw, in the characteristic way previously 

 described, thus producing soft nesting material. Here, too, it was evident 

 that the rat did not follow a certain plan by insight. It did not, for example, 

 split one piece of straw after another, but oidy grasped one piece after 

 another, making the splitting movements and dropping the straw after- 

 wards without looking at the result. Often the blade was only cracked, or 

 a small piece ripped off when it was dropped in order to grasp the next 

 blade of straw. There was only one tendency evident, namely, to let 

 certain movements run off on certain material. But by repetition of this 

 behaviour, all the straw got split eventually. Experienced rats, by the way, 

 seem to follow a plan or scheme, but that still has to be studied in detail. 



Although I was interested only in actual nest construction, I let ten of 

 the experimental animals, after testing nest building, dig in earth. They 

 did so with complete co-ordination of all digging movements. 



For the purpose of filming, three females (group (/;)) were tested when 

 pregnant. The reason was that we needed light to film but this produced 

 heat, and as is well known (Kinder, 1927) virgin females do not build a 

 sleeping nest when it is too warm. But in pregnant females, temperature 

 does not influence the behaviour as much. The urge to build a nest is then 



