632 NIDIFICATION 



GOLDFINCH, domed like that of the WREN and Bottle-Titmouse, slung 

 hammock-wise as in the case of the Golden-crested Wren and the 

 ORIOLES, or suspended by a single cord as with certain GROSBEAKS 

 and HUMMING-BIRDS. Under such circumstances it is even some- 

 times needful to balance the nest lest the weight of the growing 

 young should destroy the equipoise, and, precipitating them on the 

 ground, dash the hopes of the parents, and compensation in such 

 cases is applied by loading the opposite side of the structure with 

 lumps of earth. Certain WARBLERS (Aedon and ThamnoUa) for 

 some unascertained reason invariably lay a piece of snake's slough 

 in their nests to repel, it has been suggested, marauding lizards 

 who may thereby fear the neighbourhood of a deadly enemy. The 

 clay-built edifices of the SWALLOW and MARTIN are known to every- 

 body, and the NUTHATCH plasters up the gaping mouth of its nest- 

 hole till only a postern large enough for entrance and exit, but easy 

 of defence, is left. In South America we have the subfamily Fur- 

 nariinse (OVEN-BIRD), which construct of mud on the arching roots 

 of the mangrove or the branches of other trees globular " ovens," so 

 to speak, wherein the eggs are laid and the young hatched. The 

 FLAMINGO erects in the marshes it frequents a mound of earth some 

 two feet in height, with a cavity atop, on which the hen, having 

 oviposited, is said to sit astride with dangling legs, and in that 

 remarkable attitude perform the duty of incubation. 1 The females 

 of the HORNBILLS, and perhaps of the HOOPOES, submit to incar- 

 ceration during this interesting period, the males immuring them 

 by a barrier of mud, leaving only a small window to admit air and 

 food, which latter is assiduously brought to the prisoners. 



But though in a general way the dictates of hereditary instinct 

 are rigidly observed by Birds, in many species a remarkable degree 

 of elasticity is exhibited or the rule of habit is rudely broken. 

 Thus the noble FALCON, whose ordinary eyry is on the beetling 

 cliff, will for the convenience of procuring prey condescend to lay 

 its eggs on the ground in a marsh, or appropriate the nest of some 

 other bird in a tree. The Golden EAGLE, too, remarkably adapts 

 itself to circumstances, now rearing its young on a precipitous ledge, 

 now on the arm of an ancient monarch of the forest, and again on 

 a treeless plain, making a humble home amid grass and herbage. 

 HERONS also shew the same versatility, and will breed according to 

 circumstances in an open fen, on sea-banks or (as is most usual) on 

 lofty trees. Such changes are easy to understand. The instinct 

 of finding food for the family is predominant, and where most 

 food is there will the feeders be gathered together. This explains, 

 in all likelihood, the associated bands of OSPREYS or Fish-Hawks, 

 which in North America breed (or used to breed) in large companies 

 where sustenance is plentiful, though in the Old World the same 



1 As before noticed (pp. 255, 256), this statement has been impugned. 



