382 THE THRUSH FAMILY 



bird sitting in a thrush's nest on three eggs of this species and three 

 of its own. 



Exactly how a bird constructs its nest is a question that often 

 suggests itself, but is not easy to answer owing to the difficulties of 

 observation. In the case of the Thrushes evidence enough is avail- 

 able to permit us to give a fairly detailed description of the process, 

 subject to verification. The bird begins by bringing in its beak to the 

 site chosen the rough material for the foundation and frame of the 

 nest, arranging it so that it gradually takes roughly the form of a cup, or, 

 in any case, so that there is in the middle a hollow into which the bird 

 can get. A pair of blackbirds, which were watched at close quarters 

 through a greenhouse window, began by erecting a flat platform of 

 rootlets, twigs, and grass stalks. They then piled the material on the 

 margin of the platform, leaving the centre as it was. Each bird laid 

 his contribution on the top of the growing circular wall of the nest, 

 and then stood upon it, pressing it down with the bill, first on one 

 side, then on the other. The cock occupied about a minute at this 

 work, the hen much more, as she was not content to press in her own 

 stalk, but overhauled the work of her mate, and added finishing 

 touches to the whole structure. On the morning of the third day's 

 operations the hen was seen inside the nest shaping the cup with her 

 breast. 1 When thus shaping the interior of the nest, the bird turns 

 round and round, pressing with its feet and breast, also, possibly, 

 adding the pressure of its wings, which are kept half spread. The 

 work is done with such energy that the builder has at times to pause 

 with open beak to recover breath and strength. The pressure from 

 inside outwards would be met from outside inwards by the supporting 

 branches or twigs forming the site. On any side from which these 

 were absent the exterior of the structure would probably have the 

 rough, loose appearance of the nest shown in the photograph by Mr. 

 Taylor on Plate xin., p. 318. The top and outside edge of the rim are 

 finished off, sometimes at least, by pressing hard against it with the 



1 C. Kingsley Siddal (in litt.). 



