the undergrowth and in the gorse bush in which the nest was
placed, no trace of the third bird was to be found. Of the two remaining
young, one was alive and responsive but the other was dead, and though
the female attended assiduously to the sole surviving offspring, yet it
too had succumbed by the following morning.

In a third territory, there was a nest containing four eggs. These eggs
were due to hatch at much the same time as those in the two nests just
referred to, but they failed to do so, and an examination showed that
they contained well developed but dead chicks.

To what can the death of the young and of the chicks in the eggs be
attributed? Not to any failure in the instinctive response of the
females, for they fed their young, they brooded them, they even brooded
the dead as well as the living, and probably did all that racial
preparation had fitted them to do. Yet the fact that the young in the
second nest were lifeless and exposed at 3 A.M. seems to betoken absence
on the part of the parents during the night, and may be interpreted as a
failure of the parental instinctive response. Let us return for a moment
to the experiments. These showed, it will be remembered, that a rise or
fall in the temperature of but a few degrees was sufficient to make an
astonishing difference in the length of time that the young were able to
survive without their parents; that when the temperature reached 58 deg.
F. the bodies of the young retained their warmth, and that under such
conditions even a night's exposure had little, if any, effect; so that
even supposing that the parents were absent during the night, the death
of the young cannot be said to have been due to a failure of the
parental instinct, because under normal conditions--and under such has
their instinctive routine been evolved--their absence would not have
prejudiced the existence of the offspring. I attribute the collapse of
the young solely to the exceptional cold that prevailed at just the most
critical time, and I base this conclusion partly on the experience
gained from experiment, but mainly on their condition observed at
different intervals; for during exposure they collapsed rapidly, their
flesh became cold and their movements sluggish, their response grew
weak, and gradually they became more and more feeble until they could
scarcely close their bills after the mandibles had been forced asunder.
Yet, even after having reached so acute a stage of coll