116 NATURAL SELECTION v 
‘Parsons Pond,’ in Newfoundland, which is separated from 
the sea only by a high pebbly beach. Within the period 
above stated high tides and heavy seas have shifted the course 
of the brook flowing from the lake into the sea, and caused a 
greater, and consequently a more rapid fall of fresh water, 
which has so shallowed that part of the lake where the gulls 
were in the habit of breeding that it was no longer safe to 
build on rocks easily accessible to their common enemy, the 
fox. They therefore betook themselves to some neighbouring 
spruce and balsam firs not much over a hundred yards distant 
from their old breeding station.” Audubon also notes a 
similar change of habit, some herring-gulls building their nests 
in spruce-trees on an island in the Bay of Fundy, where they 
had formerly built on the ground. 
A curious example of a recent change of habits has oc- 
curred in Jamaica. Previous to 1854 the palm swift 
(Tachornis phoenicobea) inhabited exclusively the palm trees 
in a few districts in the island. A colony then established 
themselves in two cocoa-nut palms in Spanish Town, and 
remained there till 1857, when one tree was blown down and 
the other stripped of its foliage. Instead of now seeking out 
other palm trees the swifts drove out the swallows who built 
in the piazza of the House of Assembly, and took possession 
of it, building their nests on the tops of the end walls and at 
the angles formed by the beams and joists, a place which they 
continue to occupy in considerable numbers. It is remarked 
that here they form their nest with much less elaboration than 
when built in the palms, probably from heing less exposed. 
But perfection of structure and adaptation to purpose are 
not universal characteristics of birds’ nests, since there are 
decided imperfections. in the nesting of many birds which are 
quite compatible with our present theory, but are hardly so 
with that of instinct, which is supposed to be infallible. The 
passenger pigeon of America often crowds the branches with 
its nests till they break, and the ground is strewn with 
shattered nests, eggs, and young birds. Rooks’ nests are 
often so imperfect that during high winds the eggs fall out ; 
but the window-swallow is the most unfortunate in this re- 
spect, for White, of Selborne, informs us that he has seen them 
build, year after year, in places where their nests are liable 
