632 NIDIFICA TION 
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 HumMMING-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 Thamnobia) 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 Pur- 
nariine (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. The females 
of the HORNBILLS, and perhaps of the Hoopors, 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. 
