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 (Mercwrialis 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 Chirononiude. 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 terri- 
tories, 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, 
6 
