BRITISH WARBLERS
suddenly and in large numbers. I do not think that this is due solely to the fact that the species is more plentiful, but that it is more customary for them to migrate in companies. The behaviour of the males on their first arrival rather points to this conclusion, for it is not unusual to see two, or even three, keeping company during the early hours of the first day, one having more the appearance of a leader, although more probably the owner of the immediate surrounding territory, and in that sense only a leader. Thus they travel in search of food amongst the undergrowth and bushes, even on the ground, hidden from view by the Dog's Mercury (Mercurialis perennis), but disclosing the direction in which they are moving by shaking the leaves as they pass. Or they wander amongst the fruit trees, examining the swelling buds for Chironomidæ. How long they thus keep company it is difficult to say; apparently during a few hours only, for where three could be seen in the morning one only will be found in the evening, and adjoining territories, previously unoccupied, will each possess an owner.
Both sexes are of an excitable disposition, the male more so perhaps than the female, and the result of this is that the period of sexual activity is full of changing scenes, which are difficult to interpret. But the one outstanding feature is the law which obtains among them as to breeding territory, and in the light of this principle some of these scenes seem to me to become more intelligible. For each male has a territory, wherein it seeks its food and ultimately rears its young, the boundaries of which, as I shall presently mention, it occasionally, but only for a short time, crosses.
The migration of the sexes overlaps, but the first female appears after the first male, the time varying with the seasons, according to the early or late arrival of the males. If, that is to say, the males are very late the females may commence to arrive even on the following day, but that is not usual, some days generally intervening. Therefore if two adjoining territories are kept under observation it will be found that,
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