BIEDS — NIDIFICATION. 295 



unfolded to iis, and this from the circumstance of its not hatch- 

 ing its own eggs, which, instead of being incubated in the usual 

 way, are deposited in mounds of mixed sand and herbage, and 

 there left for the heating of the mass to develop the young, 

 which, when accomplished, force their way through the sides of 

 the mound, and commence an active life from the moment they 

 see the light of day.^ 



Sir Greorge Grrey measured one of these mounds, and 

 found it to be 'forty-five feet in circumference, and if 

 rounded in proportion on the top (it being at the time 

 unfinished) would have been full five feet high.' The heat 

 round the eggs was taken to be 89°. 



A curious aberration of the nest-building instinct is 

 sometimes shown by certain birds — particularly the com- 

 mon wren — which consists in building a supernumerary 

 nest. That is to say, after one nest is completed, another 

 is begun and finished before the eggs are laid, and the 

 first nest is not used, though sometimes it is used in pre- 

 ference to the second. 



As showing at once the eccentricity which birds some- 

 times display in the choice of a site, and also the deter- 

 mination of certain birds to return to the same site in 

 successive years, I may allude to the case published by 

 Bingley, of a pair of swallows which built their nest upon 

 the wings and body of a dead owl, which was hanging 

 from the rafters of a barn, and so loosely as to sway about 

 with every gust of wind. The owl with the nest upon ^ it 

 was placed as a curiosity in the museum of Sir Ashton 

 Lever, and he directed that a shell should be hung i^pon 

 the rafters in the place which had been previously oc- 

 cupied by the dead owl. Next year the swallows re- 

 turned and constructed their new nest in the cavity of the 

 shell.2 



The following is quoted from Thompson's ' Passions of 

 Animals,' p. 205 : — 



The sociable gi'osbeak of Africa is one of the few instances 

 of birds living in community and uniting in constructing one 



' Gould, Birds of Australia, vol. ii., p. 165, where see for further de- 

 scription. 



2 Animal Biography, vol. ii., p. 204. 



