214 A HISTORY OF BIRDS 



It would seem that the "field-naturalists " as a general- rule — 

 for there are notable exceptions — find more pleasure in nest- 

 robbing than in nest-watching ; for though they have been as- 

 siduous in recording the number of eggs in a clutch, variations 

 in colour and size, and in the choice of nesting site, their contri- 

 butions towards our knowledge of the brooding habits of birds 

 are singularly few and miserably incomplete. 



The early stages of the development of the chick begins 

 within the body of the parent, but all further growth is sus- 

 pended directly the egg is laid, to start afresh with the brood- 

 ing of the parent. While in the majority of birds this does not 

 begin until the whole complement of eggs has been laid, in 

 some cases incubation begins with the first egg, as among the 

 diurnal birds of prey and the Owl, for example, so that the late 

 eggs are partly incubated by the earlier hatched nestlings. 



Monogamous species would appear generally to share the 

 duties of incubation, as may be seen by the bare and somewhat 

 inflamed area of the abdominal wall of the body of the sitting 

 bird due to the increased flow of blood to this area, whereby 

 the necessary warmth for the developing chick is supplied. 

 But a careful analysis of the species in which this division of 

 labour obtains is yet wanting. In many cases, however, the 

 work of incubation is performed by the hen only, who, forsaken 

 by her mate, sits assiduously, leaving her charge only at distant 

 intervals for the purpose of procuring food and for defecation. 

 This last act is performed as far as possible away from the nest, 

 and is delayed until the cloaca becomes unable to bear further 

 strain. With some species, however, the hen is constantly sup- 

 plied with food at this time by her mate. In the case of 

 Montagu's Harrier, for example, the cock so waits upon the 

 hen. At his approach with food she flies out to meet him, 

 whereupon he drops his spoils, to be caught by her in mid- 

 air and borne back to the neighbourhood of the nest to be 

 devoured. The little Red-backed Shrike is most attentive at 

 this time, feeding her as she sits upon her nest. Similarly, 

 the female Blue-tit, and indeed quite a number of species, are 

 fed, when sitting, by the male. Where both parents sit, how- 

 ever, no feeding appears to be done, each providing for itself 

 when released from the cares of incubation. The hen Hoopoe, 

 save when moved by necessity, does not stir from the nest 



