Scientific ornithologists recognise this great difference between the two faunas, and include the Himalayas in the Palæarctic region, while the plains form part of the Oriental region.
The chief things which affect the distribution of birds appear to be food-supply and temperature. Hence it is evident that in the Himalayas the avifauna along the snow-line differs greatly from that of the low, warm valleys. The range of temperature in all parts of the hills varies greatly with the season. At the ordinary hill stations the minimum temperature in the summer is sometimes as high as 70°, while in the winter it may drop to 23° F. Thus in midwinter many of the birds which normally live near the snow-line at 12,000 feet descend to 7000 or 6000 feet, and not a few hill birds leave the Himalayas for a time and tarry in the plains until the severity of the winter has passed away.
THE COMMON BIRDS OF THE WESTERN HIMALAYAS
THE CORVIDÆ OR CROW FAMILY
This family, which is well represented in the Himalayas, includes the true crows, with their allies, the choughs, pies, jays, and tits.
The common Indian house-crow (Corvus splendens), with which every Anglo-Indian is only too familiar, loveth not great altitudes, hence does not occur in any of the higher hill stations. Almora is the one place in the hills where he appears to be common. There he displays all the shameless impudence of his brethren in the plains.
The common crow of the Himalayas is the large all-black species which is known as the Indian corby or jungle crow (C. macrorhynchus). Unlike its grey-necked cousin, this bird is not a public nuisance; nevertheless it occasionally renders itself objectionable by carrying off a chicken or a tame pigeon. In May or June it constructs, high up in a tree, a rough nest, which is usually well concealed by the thick foliage. The nest is a shallow cup or platform in the midst of which is a depression, lined with grass and hair. Horse-hair is used in preference to other kinds of hair; if this be not available crows will use human hair, or hair plucked from off the backs of cattle. Those who put out skins to dry are warned that nesting crows are apt to damage them seriously. Three or four eggs are laid. These are dull green, speckled with brown. Crows affect great secrecy regarding their nests. If a pair think that their nursery is being looked at by a human being, they show their displeasure by swearing as only crows can, and by tearing pieces of moss off the branch of some tree and dropping these on the offender's head!
Two species of chough, the red-billed (Graculus eremita), which is identical with the European form, and the yellow-billed chough (Pyrrhocorax alpinus), are found in the Himalayas; but he who would see them must either ascend nearly to the snow-line or remain on in the hills during the winter.