le to the point of
exhaustion, or, as has been reported, to the point of death; it is not
for nothing that Puffins fight with such desperation. And surely success
will be attained by that pair whose emotional tone stands high and whose
impulse to fight is therefore strong, rather than to the ill-assorted
couple.

The argument, then, is briefly this. In the spring, a marked change
takes place in the character of the males of very many species; instead
of being gregarious they either avoid one another and become hostile,
or, if their conditions of existence require that they shall still live
together, they become irritable and pugnacious. This change is made
known to us by the battles of varying degrees of severity which are such
a feature of bird life in the spring; and since a female can commonly be
observed to accompany the combatants, the possession of a mate appears
at first sight to be the proximate end for which the males are
contending. But when the circumstances which lead up to the quarrels are
investigated closely, the problem becomes more difficult; for it is not
merely a question of males fighting in the presence of a female, as is
generally supposed to be the case, but on the contrary there is a
complexity of strife which is bewildering--males attack females or _vice
versa_; female fights with female; or a pair combine to drive away
another pair, or even a solitary individual no matter of which sex. This
complexity of strife makes against the view that the possession of a
mate is the reason of the fighting. But an even stronger objection is to
be found in the fact that males are hostile when no female is
present--and hence we must seek elsewhere for the true explanation.

Now if the behaviour of a male be closely observed, it will be found
that its pugnacious instinct gains or loses susceptibility according to
the position which it happens to occupy--when its ground is trespassed
upon, the impulse to fight is strong; but when it crosses the boundary
it seems to lose all interest in the intruder. Moreover, in some
species, the male rejoins the flock at intervals during the early part
of the season and for a time leads a double existence, passing backwards
and forwards between its territory and the neutral ground. Its behaviour
under these circumstances affords some valuable evidence, for the bird
displays little if any hostility when accompanying the flock, yet when
it returns to the ground over which it e