WHITETHROAT 
whereas the male in the one case may have arrived only a 
few days before the male in the other, an interval of as much 
as fourteen days may separate the arrival of the respective 
females. Now there is little doubt that it is the presence 
of a female in a certain territory that is one, though not the 
only, cause which induces the unpaired male in an adjoining 
territory to cross the boundary. The impulse to approach 
the female is at this period probably irresistible, and the result 
is that the owner frequently attacks the intruder by flying 
at and pecking him vigorously until he leaves, although this 
does not always happen, for he sometimes takes little or 
no notice of him. On these occasions the female shows that 
she, too, is under the influence of considerable excitement, 
spreading and flirting her tail, and at the same time in- 
cessantly uttering her quiet call note. When the one male 
pursues the other she also accompanies them, flying rapidly 
in and out of the bushes. I never remember seeing her 
actually attack an intruding male, but when a second 
female intrudes she does not hesitate to do so; the attack 
being very vigorous, and at such times the erection of the 
feathers and the spreading and the flirting of the tails are 
in every way similar to what one observes in the case of 
the males. | 
It is more difficult to understand what causes an unpaired 
male to cross its boundary and enter the territory of another 
single male, yet it is of frequent occurrence. In assuming 
that all these activities have some direct bearing upon the 
history of the individual and of the species, we may possibly 
be in error; but, if this is so, we must still regard them as 
an expression of some agency at work in the bird’s metabolism, 
and thus they come to have a meaning equally important if 
we could but fathom it. When an unpaired male thus enters 
the adjoining territory of another single male a battle—or 
what frequently has every appearance of a battle—ensues; at 
one moment so strenuous that there need be no hesitation in 
pronouncing it as such, but at another less active and more 
7 
