BIOPSYCHOLOGICAL 6oi 



had done before. The observer removed the pigeon again and retired 

 to the house, where he saw precisely the same performance. In 

 fact, the experiment was repeated several times, always with the 

 same result. When the observer remained standing near the dovecot, 

 the pigeon did nothing; when he went into the house, the pigeon 

 immediately lifted the jamming piece of wood and slid the door 

 along. After the observations had lasted for about three-quarters of 

 an hour they were discontinued, partly because nothing new had 

 happened, and partly because the cock pigeon became exceedingly 

 impatient to take up his position on the nest. We have given the 

 case in detail, because it is a good illustration of the kind of behaviour 

 that must be called intelligent, though the prompting of the whole 

 was instinctive. There are four points to be noticed: {a) the dexterous 

 sliding of the door along; (b) the removal of the piece of wood that 

 prevented the door being opened far enough; (c) the cessation of 

 endeavour when the pigeon perceived that his solution of the 

 problem did not meet with its due reward; and {d) the immediate 

 repetition of the activity when there seemed to be a chance of 

 success. 



Unusual Hints of Intelligence.— Part of the schoolboy lore 

 of long ago was that if you took one egg out of a clutch the parent 

 bird "would not notice", but if you took two it would desert. This 

 belief in a power of appreciating numbers has been held by 

 naturalists wiser than schoolboys ; and cases are on record of both 

 birds and mammals that behaved as if they missed a member of 

 their flock or family who had been secretly removed. But when a 

 parent leads about its young ones for a considerable time it has 

 probably an awareness of each little individuality, and might be 

 perturbed by its absence without being able to verify this by 

 counting. It is certainly not by counting heads that the bees of a 

 hive became quickly aware of the fact that the queen has been 

 removed. 



It is held by some sportsmen that rooks and the like are not 

 deceived when all the intruding eliminators walk away save one, 

 who remains in concealment. Yet it may be that the rook does not 

 say to itself, "Six came and five have gone, therefore one remains." 

 Fine-brained bird it certainly is, but one must first make sure that 

 it did not notice the sportsman's concealment. Romanes reported 

 long ago an interesting case where two crows on their nest were 

 not deceived when three men threatened them and two went away, 

 while the third slipped quickly into a shed. Nor were they deceived 

 when four came and three went. But when five came and four went, 

 the crows did not notice and came down from their nest. The 

 inference was that the crows could not count beyond four, yet it 

 may have been that the rapid act of concealment was more difficult 

 to detect as the numbers increased. 



