were to lapse directly the young were hatched,
that the boundaries were to cease to exist, and that the birds were free
to wander at will without fear of molestation, the end for which the
territory had been evolved would none the less have been obtained; for
inasmuch as the parents are accompanied by their young, it matters not
in what part of the meadow they seek their food; all that matters is
that the number of families shall not exceed the available supply of
food. So far, then, as the Lapwing is concerned, the territory fulfils
its purpose when once it limits the number of males, since, by doing so,
it limits the number of families and prevents undue pressure upon the
means of support.

Nevertheless, there are many birds that seem to rely entirely upon the
territory to supply them with all that is necessary. Each Warbler seeks
its food within the precincts of its own particular domain, and, except
in occasional instances, neither resorts to neutral ground nor makes
excursions into the locality immediately surrounding the territory, as
does the Bunting. Probably it would be disastrous if it attempted to do
so, for since its young at birth are so delicate and so susceptible to
changes of temperature, it cannot afford to be absent from them for
long. Of the two experiments made with young Whitethroats, one was made
under favourable and the other under unfavourable conditions. In this
latter case the temperature was 50 deg. F., and the young, it may be
remembered, only survived for a little over one hour. Now exposure at
that temperature is evidently dangerous, but it would be still more
dangerous if the weather were wet instead of dry, and the temperature
46 deg. F. instead of 50 deg. F.; and it is, I imagine, on this account
that the impulse to brood is so strongly implanted in the female. No
sooner, it seems, does she depart than she returns with a small quantity
of food which she hurriedly distributes and immediately settles down to
brood; and if forcibly prevented from returning, her attitude betrays
symptoms of what, humanly speaking, we should term great distress. If,
then, the conditions in the external environment were such as would make
it difficult for the female to obtain food rapidly, what advantage would
she derive from so strongly developed an impulse? Might it not be a
disadvantage? Might it not mean that she would abandon the search too
readily and be content to return with an insufficient supply, and