From the time of the laying of the first egg until the moment of the departure of the last young bird, one or other of the parents always mounts guard over the nest, except when they are chasing a koel.  Crows are confirmed egg-lifters and chicken-stealers; they apply their standard of morality to other birds, and, in consequence, never leave their own offspring unguarded.  A crow’s nest at which there is no adult crow certainly contains neither eggs nor young birds.

As has already been stated, crows spend, much time in teasing and annoying other birds.  Retribution overtakes them in the nesting season.  The Indian koel (Eudynamis honorata) cuckolds them.  The crows either are aware of this or have an instinctive dislike to this cuckoo.  The sight of the koel affects a crow in much the same way as a red cloth irritates a bull.  One of these cuckoos has but to perch in a tree that contains a crow’s nest and begin calling in order to make both the owners of the nest attack him.  The koel takes full advantage of this fact.  The cock approaches the nest and begins uttering his fluty kuil, kuil.  The crows forthwith dash savagely at him.  He flies off pursued by them.  He can easily outdistance his pursuers, but is content to keep a lead of a few feet, crying pip-pip or kuil-kuil, and thus he lures the parent crows to some distance.  No sooner are their backs turned than the hen koel slips quietly into the nest and deposits an egg in it.  If she have time she carries off or throws out one or more of the legitimate eggs.  When the crows return to the nest, having failed to catch the cock koel, they do not appear to notice the trick played upon them, although the koel’s egg is smaller than theirs and of an olive-green colour.  Through the greater part of June and July the koels keep the crows busy chasing them.  Something approaching pandemonium reigns in the neighbourhood of a colony of nesting crows:  from dawn till nightfall the shrieks and yells of the koels mingle with the harsh notes of the crows.

Sometimes the crows return from the chase of the cock koel before the hen is ready, and surprise her in the nest; then they attack her.  She flees in terror, and is followed by the corvi.  Her screams when being thus pursued are loud enough to awaken the Seven Sleepers.  She has cause for alarm, for, if the raging crows catch her, they will assuredly kill her.  Such a tragedy does sometimes occur.

Not infrequently it happens that more than one koel’s egg is laid in a crow’s nest.

The incubation period of the egg of the koel is shorter than that of the crow, the consequence is that when, as usually happens, there is one of the former and several of the latter in a nest, the young koel is invariably the first to emerge.  It does not attempt to eject from the nest either the legitimate eggs or the young crows when they appear on the scene.  Indeed, it lives on excellent terms with its foster brethren.  But to say this is to anticipate, for as a rule, neither young koels nor baby crows hatch out until July.