136 INTELLIGENT BEHAVIOUR 
line with the finer materials, just as a wild goldfinch would 
do.” 
Experiment seems, therefore, to show in a way, and with a 
clearness impossible of attainment by observation under natural 
uncontrolled conditions, that nest-building in birds is instinc- 
tive. That the manner and method of procedure is often 
modified in accordance with special conditions—that the in- 
stinctive outline of nidification receives its final touches 
through individual experience—is sometimes seen under 
nature, and more often under the semi-experimental conditions 
of domestication. Thus three pairs of pigeons in the Wilson 
Tower of Clifton College made their nests in 1898, as I am 
informed by Mr. H. C. Playne, of galvanized iron wire, pieces 
of which were left in a corner at the top of the tower, thus 
affording a parallel to the behaviour of the unconventional 
crow of Calcutta, mentioned by Mr. J. W. Headley,* which 
made its nest of soda-water bottle wires, which it picked up in 
a back yard. But even in this matter experiment serves to 
bring out clearly the selective influence which is exercised by 
intelligence. Bolton,f in 1792, observed a pair of goldfinches 
beginning to build their nest in his garden. They formed the 
ground-work of moss, grass, etc., as usual ; but on his scatter- 
ing small parcels of wool in different parts of the garden they, 
in great measure, left off the use of their own stuff and used 
the wool. Afterwards he gave them cotton, and they then 
used this instead of the wool; then he supplied fine down, and 
they finished their work with this, leaving the wool and 
cotton. 
Tn studying the behaviour of wild animals under natural 
conditions, it must always be difficult to distinguish the con- 
genital basis from the acquired elements ; for both tend to 
bring about a working adjustment to the conditions of life, 
and we can seldom have opportunities of tracing the, interplay 
of the factors which produce the instinct-habits of adult life. 
* « The Structure and Life of Birds,” p. 335. 
+ Preface to “ Harmonia Ruralis,” quoted by Yarrell, “ British Birds,” 
vol. i., p. 541, ‘ 
