ve had to travel a little
farther; but even if they had been compelled to do so, their absence
would only have been prolonged by so many minutes the more, and under
normal conditions what harmful result to the offspring could possibly
have followed? The question for us, however, is not what might have
occurred under normal conditions, but whether the life behaviour is so
adjusted as to meet the exigencies of diverse, and in this case of
abnormal, circumstances. Now the capacity of the young to resist
exposure diminishes very rapidly when the temperature falls below the
normal--the danger zone seems to be reached at approximately 52 deg. F.,
and the length of time during which they survive then becomes
astonishingly short--and moreover the fall in the temperature would tend
to decrease the supply of insect life upon which they depend, so that if
the size of the territories had been reduced by one half, and the parents
in consequence had been compelled to seek their food at a greater
distance, can it be doubted that the cumulative effect of even a few
minutes of additional exposure would have been detrimental, if not
disastrous, to the offspring?

We speak, however, of the parents extending their journeys a little
farther in this direction or a little farther in that, as though they
could do so with impunity except in so far as it affected themselves, or
their offspring, or the other Yellow Buntings inhabiting that particular
area. But, most certainly, any extension would have meant so much
encroachment upon the available means of support of other members of the
species inhabiting adjoining areas, whose young in turn would have been
liable to have been affected; and, with even greater certainty, the
Whitethroats, the Stonechats, the Tree-Pipits, and the Willow-Warblers
that had also established themselves in that one corner of the Common
would have been hard pressed to find sufficient food with sufficient
rapidity.

Let me give another illustration of a somewhat different kind. Lapwings,
as we saw in the previous chapters, establish territories and guard them
from intrusion with scrupulous care. The young are able to leave the
nest soon after they are hatched, and consequently the parents are not
necessarily obliged to bring food _to_ them--they can, if they so
choose, lead them _to_ the food. Whether each pair limits its search for
food to its territory, I do not know. But even supposing that all
ownership of territory