232 ELEMENTS OF ORNITHOLOGY. 
bright (as the Kingfisher), or both dull (as the Swift), build 
in holes or covered nests; while others, in which the female 
is the duller, make covered nests, as especially in the genus 
Matlurus. 
The Savannah Cuckoo (Crotophaga ani) is said to be a social 
nest-builder, several Birds using a nest in common. The 
Weaver-birds of Africa, however, practice the most curious, 
social nidification. They form nests associated together in large 
masses, which are pendent, with a stocking-like entrances 
funnel, by which they better avoid the attack of snakes, The 
Birds construct together the general cover which is common 
to and protects all their nests. Then, underneath this cover 
and suspended from it, they separately form their individual 
nests placed closely side by side. New nests are annually con- 
structed beneath, and suspended from, the older ones, till the 
whole mass becomes too heavy for their support and gives 
way. Then the labour is recommenced in another locality. 
As everyone knows, the Cuckoo builds no nest, but places 
its egg in the nests of other Birds. The same is the case with 
the Cow-bird of the New World (Molothrus pecoris), and the 
Argentine Cow-bird (Molothrus bonariensis) is singularly irre- 
gular in its modes of laying. But some other birds occasion- 
ally do the same, from stupidity or otherwise, Pheasants’ and 
Partridges’ eggs being often laid in the same nest. 
Generally each species adheres to one mode of nidification, 
but sometimes this will vary. The Heron will breed in trees 
or in open fens, according to circumstances, and the Falcon 
and Golden Eagle will show an analogous versatility from 
rocky cliff to plain. The Water-hen will often build in trees in 
districts liable to sudden floods. 
The male very often sings zealously while his mate is sitting, 
his song stopping short when the eggs are hatched, though it 
will be renewed should the young be destroyed very quickly, 
the female then laving again, perhaps in a new nest. Some 
Birds, however, as the Robin and the Wren, will sing their 
song all the year round, save at moulting-time and in severe 
weather. Skylarks and Thrushes also sing after their moult, 
but their notes have not the force and melody of the spring, 
and, indeed, the sounds uttered by Birds are specially related 
to the breeding-season, whether those sounds be whistles, 
screams, hoots, bleatings, drumming, or booming sounds, 
or whatever they may be. Akin to these vocal utterances 
