A NEW MIGRATION.
An old -theory on the migration of birds is weakened, if not destroyed, by news which reaches me from Madagascar, and 1 have found corroboration from other sources. It has been held that-birds migrate freely over shallow seas and not over deep • and the two standard examples are—on the positive side, the North Sea which is very shallow and a faVourite route ; and on the negative side the very deep channel between Madagascar and the mainland, which acts as a complete harrier. The inference is that migration over seas is a survival from a slower land migration learnt by remote ancestors. Observations on the appearance of swifts in Madagascar suggest either that the theory is wrong or that some birds at long last are discovering the wisdom of crossing such unknown seas. My own knowledge of African birds is much too scanty to justify any opinion ; but the facts may interest the most insular.
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