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116 NATURAL SELECTION v'Parsons Pond,' in Newfoundland, which is separated fromthe sea only by a high pebbly beach. Within the periodabove stated high tides and heavy seas have shifted the courseof the brook flowing from the lake into the sea, and caused agreater, and consequently a more rapid fall of fresh water,which has so shallowed that part of the lake where the gullswere in the habit of breeding that it was no longer safe tobuild on rocks easily accessible to their common enemy, thefox. They therefore betook themselves to some neighbouringspruce and balsam firs not much over a hundred yards distantfrom their old breeding station." Audubon also notes asimilar change of habit, some herring-gulls building their nestsin spruce-trees on an island in the Bay of Fundy, where theyhad formerly built on the ground.A curious example of a recent change of habits has occurredin Jamaica. Previous to 1854 the palm swift(Tachornis phoenicobea) inhabited exclusively the palm treesin a few districts in the island. A colony then establishedthemselves in two cocoa-nut palms in Spanish Town, andremained there till 1857, when one tree was blown down andthe other stripped of its foliage. Instead of now seeking outother palm trees the swifts drove out the swallows who builtin the piazza of the House of Assembly, and took possessionof it, building their nests on the tops of the end walls and atthe angles formed by the beams and joists, a place which theycontinue to occupy in considerable numbers. It is remarkedthat here they form their nest with much less elaboration thanwhen built in the palms, probably from being less exposed.But perfection of structure and adaptation to purpose arenot universal characteristics of birds' nests, since there aredecided imperfections in the nesting of many birds which arequite compatible with our present theory, but are hardly sowith that of instinct, which is supposed to be infallible. Thepassenger pigeon of America often crowds the branches withits nests tillthey break, and the isground strewn withshattered nests, eggs, and young birds. Books' nests areoften so imperfect that during high winds the eggs fall out ;but the window-swallow is the most unfortunate in this respect,for White, of Selborne, informs us that he has seen thembuild, year after year, in places where their nests are liable