more variable than the wind—nothing more variable than the wind during the vernal and autumnal equinoxes, when birds must migrate—blowing, as it does, from every point of the compass in twenty-four hours. Were the birds' movements mainly dependent on air-currents, and air-currents only, we should rarely—although Mr. Rowley assumes the contrary—have year by year the same phenomena occurring at any given locality on our east coast. The arrival or non-arrival of immigrants being dependent on one of the most variable of causes, the results would also be variable, whereas the contrary is the case.
Wind, I am convinced, except in some very abnormal instances,[1] as great gales and storms, has little to do with the normal phenomena of migration. All animals and man himself undoubtedly prefer favourable weather for travelling; but although they may delay, they do not put off their travels altogether because wind and weather are unpropitious.
Continuing his subject, Mr. Rowley says there is one thing in common between the migration of the seed and the bird—"once started they do not come back till the journey is finished." Does Mr. Rowley seriously wish it to be inferred that any comparison can be drawn between the two phenomena—the one thing an inert mass, the play of wind and current; the other a living, highly endowed organism. The seed returns not by the same path because it cannot, the bird because it will not. Birds are occasionally, however, known to turn back in their migratory journey when they find they have made a mistake. Several instances are on record of migrants during the autumn being seen away off the mouth of the Channel and over the Atlantic, apparently migrating in the wrong direction: they are probably such as on dark foggy morning have overshot the mark, and at daylight discovering their error, are making their way to the nearest land.
There is also the case mentioned by Mr. Stevenson ('Birds of Norfolk,' vol. i., p. 413 et seq.) of the Red-legged Partridges in Norfolk migrating out to sea and again returning. Had the birds in these instances migrated on Mr. Rowley's theory, and not by their own instinct, they ought to have kept going in a direct line without coming back. In fact, on Mr. Rowley's hypothesis, we
- ↑ See 'The Field,' March 11th and 18th, 1876, "On some Abnormal Migrations of Birds."
