SOME RESULTS OF EXPERIMENT 135 
this may be done with some approach to accuracy, resort must 
be had to experiment, which permits of observation under 
controlled conditions. 
To ascertain, for example, how far nest-building is instinc- 
tive in birds, Mr. John 8. Budgett hatched a hen greenfinch 
under a canary. In the following autumn he bought a caged 
bird, a cock, probably of the same year, and in the succeeding 
spring turned the pair into a large aviary, supplying such 
material as twigs, rootlets, dried grass, moss, feathers, sheep’s 
wool and horsehair. The hen soon began to build, the cock 
bird taking no share in the work, and finished her nest in a 
few days. On careful comparison it was found to resemble 
that of a wild greenfinch in every particular, being made of 
wool, roots, and moss, lined with horsehair. A second nest the 
aviary greenfinch built was also quite normal. 
In the case of a bullfinch which Mr. Budgett reared, having 
obtained it when a few weeks’ old, the first nest was composed 
of dried grass with a little wool and hair, but without either 
rootlets or twigs. A second which she built was, however, 
quite typical, made of fine twigs and roots, and lined with 
horsehair ; as was also a third nest. 
It is just possible, though most improbable, that the bull- 
finch utilized its three weeks’ experience gained in the nest 
from which it was taken. But Mr. Jenner Weir describes * 
observations on canaries in which this source of experience is 
excluded. “It is usual,” he says, “ with canary fanciers to 
take out the nest constructed by, the parent birds, and to place 
a felt. nest in its place, and when her young are hatched, and 
old enough to be handled, to place a second clean nest, also of 
felt, in the box, removing the other. But I never knew that 
canaries so reared failed to make a nest when the breeding 
time arrived. I have, on the other hand, marvelled to see 
how like a wild bird’s the nests are constructed. It is custo- 
mary to supply them with a small set of materials, such as 
moss and hair. They use the moss for the foundation, and 
* Ina letter to Darwin, quoted by Romanes, “Mental Evolution in 
Animals,” p. 226, 
