66 BIRDS OF LA PLATA 
in the old habit of building exposed nests would 
perish. Domed nests made by Dendrocolaptine birds 
are very abundant even now, and it is probable that, 
before the country became settled by Europeans, 
they were very much more numerous. Darwin, 
speaking of the Oven-bird’s habit of always placing 
its oven in the most conspicuous and (to man) access- 
ible places, predicts, and truly I believe, that this 
habit will eventually cause the extinction of the 
species ; for when the country becomes more thickly 
settled, the bird-nesting boys will destroy all the 
ovens. Probably when the Oven-birds were more 
abundant the Sparrows could always find vacant 
ovens to breed in, until a habit of breeding almost 
exclusively in these safe and convenient bird-built 
houses was acquired; and the present seemingly 
stupid persistence of the birds in struggling to get 
possession of those already occupied by stronger 
species, only shows that the habit or instinct has not 
been modified to suit a change in the conditions— 
ie., a diminishing number of ovens to breed in, 
with perhaps the increase of other stronger species 
possessing the same habit. But while the in- 
stinct thus survives too strongly in the country 
birds, many individuals have taken to a town life, 
and acquired the new habit of breeding in holes 
in brick walls. Probably this race of town birds 
will eventually colonise the rural districts, and 
usurp the place of the country birds, which will 
then be placed at a disadvantage. 
