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(Concluded from p. 271)
Occasionally the female parent as well as the male may kill its young.
Brook (26) had a pair of blue magpies in his aviary. The hen laid three eggs of which it ate two; the third was hatched and the youngster was fed and cared for for a week when the mother killed and devoured it.
Domesticity and captivity not infrequently produce instinctive conflict situations that lead to infanticide. The data are still relatively meager and insufficient for a thorough interpretation.
We do not know what conditions provoked any of these acts, but we can find some human parallels, at least as far as lack of care, desertion, or even killing, is concerned. Criminal human parents do not go as far as to eat their murdered offspring, but this may be due to the inhibiting influence of centuries of civilization, and of its attendant morals.
A rather peculiar feature about the cyclical emotions is that they very frequently do not overlap. Thus, in many birds the urge to display and sing in the male dies down after nest-building commences; the instinct to care for the eggs dies when they hatch and the female bird has at that time very little desire to care for and protect the young. This was first discovered by wild life photographers who found that it was easier to get pictures of the bird on the nest after incubation had gone on for several days than when it was first starting, but that as soon as the eggs hatched, it was again difficult to induce the bird to come to the nest while the photographers or their “blind “were near the nest. Each part of the cycle grows- slowly to a climax, then abruptly ceases, and only then does the next part commence to develop. When any disturbance occurs that interferes seriously with the bird's activities, it often tends to go back one step in the sequence of cyclical activities and start again from that point.