PARENTAL CARE AND NEST-MAKING 295 



to ingrained instinct. Thus we are assured that a green- 

 finch, incubated by a canary in a canary's nest, made, in the 

 course of time, a true greenfinch nest of fibrous roots, moss, 

 wool, and horse-hair. 



There is often considerable elasticity in the choice of a 

 site. The Golden-Eagle usually nests on a ledge of the clifi^, 

 but it may choose a tree. Herons typically nest on high 

 trees, but they may elect to build in an open fen. The noble 

 falcon whose eyry is typically on the beetling cliff may nest 

 in a marsh. Bird literature is full of instances of similar 

 plasticity, which are more interesting than cases of building 

 inside a station lamp or up the sleeve of a scare-crow, for it is 

 often forgotten that these curious sites have not to birds 

 anything of the significance they have for man. 



Methods of Building. — The 7fiodus operandi in nest- 

 building can hardly be described in general terms. The bird 

 uses its bill and its feet, twining and twisting the materials 

 together. When the nest begins to take shape the bird may 

 get inside and turn round and round. The hens usually 

 do most of the nest-making, but the cocks often collect 

 materials and may share in the work more intimately. In 

 the case of pigeons the cock may be seen bringing straws to 

 the female who has already begun to sit ; he mounts on her 

 back and passes the straw over her head within reach of her 

 mouth. This suggests a slight overlap of the incubatory 

 period by the more strictly sexual period. 



To appreciate the making of nests without hands, it is 

 necessary to take detailed instances. The house-martin 

 presses the tiny daubs of clay against the wall and hastens 

 slowly, for much must not be added till what has been already 

 built has hardened and set. In making their leaf nest the 

 male and female tailor-birds work together ; she gets into 

 the middle of the two or three drooping leaves, he remains 

 outside ; holes are made through the leaves and threads of 

 fibre are passed in and out — a literal sewing. The fantail 

 warbler is said to knot the thread with which it sews the leaves 

 together, and it also forms a canopy of grass-stem.s above the 

 nest. 



