Because its principal food is worms, which feed and crawl upon the humid surface of the ground in the dusk, and retire before the light of day ; and, roosting higher than other birds, the first rays of the sun, as they peep from the horizon, become visible to it. - Knapp.
Because they are scratching themselves with one foot, and thus lose their centre of gravity. - G.White.
Because rooks have a more discerning scent than starlings, and can lead them to spots more productive of food. Anatomists say that rooks, by reason of two large nerves which run down between the eyes into the upper mandible, have a more delicate feeling than other round-billed birds, and can grope for their meat when out of sight. Perhaps, then, their associates attend them from interest, as greyhounds wait on the motions of their finders, and as lions are said to do on the yelpings of jackals. - G. White.
Because, though bearing little resemblance to those of the plover, they are, in some places, not uncommonly taken, and sold as plover's eggs in the London market; and, probably, the habitual eater of them can alone distinguish a sensible difference.
Because their haunts have been disturbed by the felling of trees, in consequence of the increased value of timber, and the changes in our manners and ideas. Rooks love to build near the habitation of man ; but their delight, the long avenue, is no longer the fashion; and the poor birds have been dispersed to settle on single distant trees, or in the copse, and are captured and persecuted. In many counties, very few rookeries remain, where once they were considered as a necessary appendage, and regularly pointed out the abbey, the hall, the court-house, and the grange. - Knapp.
The following anecdote of the rook is related in the Zoological Journal, and merits introduction here, for the excellent lesson it affords to man. " A gentleman occupied a farm in Essex, where he had not long resided, before numerous rooks built their nests on the trees surrounding his premises ; the rookery was much prized ; the farmer, however, being induced to hire a larger farm about three quarters of a mile distant, he left the farm and the rookery ; but, to his great surprise and pleasure, the whole rookery deserted their former habitation, and came to the new one of their old master. It ought to be added, that this gentleman was strongly attached to all animals whatsoever, and, of course, used them kindly."
Because their food, grubs, insects, and worms, is then mostly hidden in the earth beyond their reach. At this time, were it not for its breakfast of dew-worms, which it catches in the grey of the morning, as it is appointed the earliest of risers, it would commonly be famished. In the hot summer of 1825, many of the young brood of the season perished from want; the mornings were without dew, and consequently few or no worms were to be obtained. - Knapp.