At the second nest, I was unable to watch the behaviour of the parents so closely. On the 15th June the nest contained three young from three to four days old, and during the morning of that and the succeeding day nothing unusual occurred, with the exception that the period of exposure seemed, as in the former case, to be too long. On the 17th June at 3.10 A.M. the young had collapsed and were stiff, but the parents were in their territory and anxious apparently to attend to their brood. At 9.15 A.M. only two of the young were left in the nest, and though I searched amongst 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° 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.