It is not possible for anyone of sound hearing to be an hour in a hill station in the early summer without being aware of the presence of cuckoos. The Himalayas literally teem with them. From March to June, or even July, the cheerful double note of the common cuckoo (Cuculus canorus) emanates from every second tree. This species, as all the world knows, looks like a hawk and flies like a hawk.
According to some naturalists, the cuckoo profits by its similarity to a bird of prey. The little birds which it imposes upon are supposed to fly away in terror when they see it, thus allowing it to work unmolested its wicked will in their nests. My experience is that little birds have a habit of attacking birds of prey that venture near their nest. The presence of eggs or young ones makes the most timid creatures as bold as the proverbial lion. I therefore do not believe that these cuckoos which resemble birds of prey derive any benefit therefrom.
The hen European cuckoo differs very slightly from the cock. In some species, as, for example, the famous "brain-fever bird" (Hierococcyx varius), there is no external difference between the sexes, while in others, such as the Indian koel (Eudynamis honorata), and the violet cuckoo (Chrysococcyx xanthorhynchus), the sexes are very dissimilar. I commend these facts to the notice of those who profess to explain sexual dimorphism (the different appearance of the sexes) by means of natural or sexual selection. The comfortable theory that the hens are less showily coloured than the cocks, because they stand in greater need of protective colouring while sitting on the nest, cannot be applied to the parasitic cuckoos, for these build no nests, neither do they incubate their eggs.
In the Himalayas the common cuckoo victimises chiefly pipits, larks, and chats, but its eggs have been found in the nests of many other birds, including the magpie-robin, white-cheeked bulbul, spotted forktail, rufous-backed shrike, and the jungle babbler.
The eggs of Cuculus canorus display considerable variation in colour. Those who are interested in the subject are referred to Mr. Stuart Baker's papers on the Oology of the Indian Cuckoos in Volume XVII of the Journal of the Bombay Natural History Society.
It often happens that the eggs laid by the cuckoo are not unlike those of the birds in the nests of which they are deposited. Hence, some naturalists assert that the cuckoo, having laid an egg, flies about with it in her bill until she comes upon a clutch which matches her egg. Perhaps the best reply to this theory is that such refinement on the part of the cuckoo is wholly unnecessary. Most birds, when seized by the mania of incubation, will sit upon anything which even remotely resembles an egg.
Mr. Stuart Baker writes that he has not found that there is any proof of the cuckoo trying to match its eggs with those of the intended foster-mother, or that it selects a foster-mother whose eggs shall match its own. He adds that not one of his correspondents has advanced this suggestion, and states that he has little doubt that convenience of site and propinquity to the cuckoo about to lay its eggs are the main requisitions.
Almost indistinguishable from the common cuckoo in appearance is the Himalayan cuckoo (Cuculus saturatus). The call of this bird, which continues later in the year than that of the common cuckoo, is not unlike the whoot-whoot-whoot of the crow-pheasant or coucal. Perhaps it is even more like the uk-uk-uk of the hoopoe repeated very loudly. It may be syllabised as cuck-hoo-hoo-hoo-hoo. Not very much is known about the habits of this species. It is believed to victimise chiefly willow-warblers.
The Indian cuckoo (Cuculus micropterus) resembles in appearance the two species already described. Blanford speaks of its call as a fine melodious whistle. I would not describe the note as a whistle. To me it sounds like wherefore, wherefore, impressively and sonorously intoned. The vernacular names Boukotako and Kyphulpakka are onomatopoetic, as is Broken Pekoe Bird, by which name the species is known to many Europeans.
Last, but not least of the common Himalayan cuckoos, are the famous brain-fever birds, whose crescendo brain-fever, BRAIN-FEVER, BRAIN-FEVER, which is shrieked at all hours of the day and the night, has called forth untold volumes of awful profanity from jaded Europeans living in the plains, and has earned the highest encomiums of Indians.
There are two species of brain-fever bird that disport themselves in the Himalayas. These are known respectively as the large and the common hawk-cuckoo (Hierococcyx sparverioides and H. varius). I do not profess to distinguish with certainty between the notes of these two birds, but am under the impression that the larger form is the one that makes itself heard at Naini Tal and Mussoorie.
The Indian koel (Eudynamis honorata) is not to be numbered among the common birds of the Himalayas. Its noisy call kuil, kuil, kuil, which may be expressed by the words you're-ill, you're-ill, who-are-you? who-are-you? is heard throughout the sub-Himalayan regions in the early summer, and I have heard it as high up as Rajpur below Mussoorie, but have not noticed the bird at any of the hill stations except Almora. As has already been stated, the avifauna of Almora, a little station in the inner hills nearly forty miles from the plains, is a very curious one. I have not only heard the koel calling there, but have seen a young koel being fed by crows. Now, at Almora alone of the hill stations does Corvus splendens, the Indian house-crow, occur, and this is the usual victim of the koel. I would therefore attribute the presence of the koel at Almora and its absence from other hill stations to the fact that at Almora alone the koel's dupe occurs.