SELBORNE, _May_ 13_th_, 1778.
Dear Sir,--Among the many singularities attending those amusing birds the
swifts, I am now confirmed in the opinion that we have every year the
same number of pairs invariably; at least the result of my inquiry has
been exactly the same for a long time past. The swallows and martins are
so numerous, and so widely distributed over the village, that it is
hardly possible to recount them; while the swifts, though they do not
build in the church, yet so frequently haunt it, and play and rendezvous
round it, that they are easily enumerated. The number that I constantly
find are eight pairs; about half of which reside in the church, and the
rest build in some of the lowest and meanest thatched cottages. Now as
these eight pairs, allowance being made for accidents, breed yearly eight
pairs more, what becomes annually of this increase; and what determines
every spring which pairs shall visit us, and reoccupy their ancient
haunts?
Ever since I have attended to the subject of ornithology, I have always
supposed that that sudden reverse of affection, that strange ἀντιστοργὴ,
which immediately succeeds in the feathered kind to the most
passionate fondness, is the occasion of an equal dispersion of birds over
the face of the earth. Without this provision one favourite district
would be crowded with inhabitants, while others would be destitute and
forsaken. But the parent birds seem to maintain a jealous superiority,
and to oblige the young to seek for new abodes; and the rivalry of the
males in many kinds, prevents their crowding the one on the other.
Whether the swallows and house-martins return in the same exact number
annually is not easy to say, for reasons given above; but it is apparent,
as I have remarked before in my Monographies, that the numbers returning
bear no manner of proportion to the numbers retiring.