Great changes in the avifauna take place in September.
The yellow-throated sparrows, the koels, the sunbirds, the bee-eaters, the red turtle-doves and the majority of the king-crows leave the Punjab. From the United Provinces there is a large exodus of brain-fever birds, koels, pied crested-cuckoos, paradise flycatchers and Indian orioles. These last are replaced by black-headed orioles in the United Provinces, but not in the Punjab.
On the other hand, the great autumnal immigration takes place throughout the month. Before September is half over the migratory wagtails begin to appear. Like most birds they travel by night when migrating. They arrive in silence, but on the morning of their coming the observer cannot fail to notice their cheerful little notes, which, like the hanging of the village smoke, are to be numbered among the signs of the approach of winter. The three species that visit India in the largest numbers are the white (Motacilla alba), the masked (M. personata) and the grey wagtail (M. melanope). In Bengal the first two are largely replaced by the white-faced wagtail (M. leucopsis). The names "white" and "grey" are not very happy ones. The white species is a grey bird with a white face and some black on the head and breast; the masked wagtail is very difficult to distinguish from the white species, differing in having less white and more black on the head and face, the white constituting the "mask"; the grey wagtail has the upper plumage greenish-grey and the lower parts sulphur-yellow. The three species arrive almost simultaneously, but the experience of the writer is that the grey bird usually comes a day or two before his cousins.
On one of the last ten days of September the first batch of Indian redstarts (Ruticilla frontalis) reaches India. Within twenty days of the coming of these welcome little birds it is possible to dispense with punkas.
Like the redstarts the rose-finches and minivets begin to pour into India towards the end of September. The snipe arrive daily throughout the month.
With the first full moon of September come the grey quail (Coturnix communis). These, like the rain-quail, afford good sport with the gun if attracted by call birds set down overnight. When the stream of immigrating quail has ceased to flow, these birds spread themselves over the well-cropped country. It then becomes difficult to obtain a good bag of quail until the time of the spring harvest, when they collect in the crops that are still standing.
Thousands of blue-winged teal invade India in September, but most of the other species of non-resident duck do not arrive until October or even November.
Not the least important of the September arrivals are the migratory birds of prey. None of the owls seem to migrate. Nor do the vultures, but a large proportion of the diurnal raptores leaves the plains of India in the spring.
To every migratory species of raptorial bird, that captures living quarry, there is a non-migratory counterpart or near relative. It would almost seem as if each species were broken up into two clans—a migratory and a stationary one. Thus, of each of the following pairs of birds the first-named is migratory and the other non-migratory: the steppe-eagle and the tawny eagle, the large Indian and the common kite, the long-legged and the white-eyed buzzard, the sparrow-hawk and the shikra, the peregrine and the lugger falcon, the common and the red-headed merlin, the kestrel and the black-winged kite.
It is tempting to formulate the theory that the raptores are migratory or the reverse according or not as they prey on birds of passage, and that the former migrate merely in order to follow their quarry. Certain facts seem to bear out this theory. The peregrine falcon, which feeds largely on ducks, is migratory, while the lugger falcon—a bird not particularly addicted to waterfowl—remains in India throughout the year.