178 



A HISTORY OF BIRDS 



acquired this habit should continue to make similar preparations 

 for brooding when for some other reason — to escape floods or 

 enemies — they elected to build in trees, instead of reverting to 

 the older custom of seeking a hole in the trunk thereof. Such 

 a nest would necessarily be of a loose and rough character, 

 but, since it served its purpose, many to this present day have 

 not improved thereon. The Crows, Pigeons, Herons, and 

 Accipitrine birds, such as the Eagles, for example, build only 

 a rough platform of sticks. In the case of the Pigeons it is so 

 frail indeed that daylight can be seen through it. Nevertheless, 

 these structures are much more durable than one might sup- 

 pose, and in successive seasons are often either repaired or a 

 fresh nest is built upon the top of the old one, a practice 

 followed by many birds of prey, until at last, as in the case of 

 th^ Osprey, for instance, the accumulated mass, if built in a 

 tree, falls of its own weight. 



III. 24. — Nest of the Hammer Head 



Some species, however, have improved upon this platform 

 structure, piling up sticks to form a roof or dome, such as, for 

 example, may be seen in the nests of the Magpie, the African 

 "Hammer-head" {Scopus umbrettd) and the Quaker-parrot 



