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Let us consider the case of a bird which normally spends the winter in north-west Africa, on either side of the tropic of Cancer. It arrived there probably in November from this country, and there it will stay until the migratory urge sets it flying north again. When will it leave the scrub and palms of Africa for England, and how long will it take to do the journey ? As far as the exact time of departure from its winter haunts in Africa is concerned, we may have little accurate knowledge, for the recording of the arrival and departure of birds is not much done in those parts. But the date the birds reach Europe, and the time they will take to progress towards and reach, their breeding areas, may be |
