YOUNG BIRDS IN THE NURSERY 75 



soiled pieces of heather of which the nest is commonly 

 largely composed. One wonders how much of this ap- 

 parent recognition of the necessity for cleanliness is 

 " instinctive," and how much is due to, at least a vague 

 realisation of the dangers of dirt. In the case of the 

 eagle, it is significant to note, these efforts to maintain 

 cleanliness cease some time before the fledgeling is able 

 to leave the nest, so that by the time it is vacated it 

 has become exceedingly foul. 



Precocious nestlings, as we have already remarked, are 

 for the most part able to feed themselves, under parental 

 guidance as to the suitability of the food. The young 

 hoatzin furnishes an exception to the rule, but in this case 

 it is due to the peculiar environment : the food not being 

 furnished by the tree amid which the nest is placed. The 

 grebes afford another exception, for here the food is 

 furnished by small fish, necessitating a combination of 

 activities in their capture impossible to young birds. 



But with nidicolous birds the case is far otherwise. 

 These, apparently without exception, feed their young at 

 first, at any rate, on regurgitated food, in some cases after 

 it has undergone a more or less extensive process of pre- 

 digestion, sometimes only softened and mixed with saliva. 

 The young of the common sparrow and greenfinch, for 

 instance, are fed at first on regurgitated food, then on 

 insects in what we may call the raw state, and finally on 

 seeds of various kinds. 



When the young are fed on insects, the labour entailed 

 on the parents is enormous. A pair of Blue Titmice have 

 been observed to make no less than 475 journeys to the 

 nest during a day's foraging extending over seventeen 

 hours. Small wonder is there that the labours of both 



