Any observer may verify the assertion that birds regularly visit certain favourable food-bases by paying attention to the occurrences of birds of passage. The study of a county, for instance, shows that certain species show partiality for particular localities. Thus in Cheshire goldeneyes pass through every spring and autumn, and may be met with occasionally on any of the meres; but at Oakmere, in the Delamere district, one may be almost certain of seeing parties of this species any time during the periods of passage. The curlew may be heard or seen passing over any part of the county, but only in the Delamere fields do we frequently meet with flocks feeding in inland Cheshire. Before the winter resident golden plovers have arrived in autumn and after they have departed in spring, the favourite fields are regularly visited by passing flocks, and the lower reaches of the Mersey, where the common sandpiper is rare as a summer resident, are visited every autumn by parties of birds on passage. Chance may lead a casual wanderer to a good food-supplying spot, but the regularity of appearance suggests habit and memory.
A fact which supports the theory that birds ramble far in search of food in their winter quarters, is that in many species the winter range is more extensive than the breeding area. Thus Mr Cooke shows that the known breeding area of the Pacific golden plover has an east and west extension of some 1700 miles, but in winter it ranges over an area with an east and west extension of about 10,000 miles. The scarlet tanager, however, has a breeding range extending for some 1900 miles across eastern Canada and a winter home in north-western South America of only some 700 miles in extent.
The winter quarters, or the outermost limits of the individual but not necessarily the specific range, having been reached, the bird spends its time in seeking food, remaining in one place if food is plentiful, or wandering, according to necessity or the habit of the species. The assertion that some birds have a second breeding season in their southern home is either unsupported by any direct evidence or is the result of a mistake in identification; the bird which has been found breeding has in several instances been shown to be a southern form or a related species of the one it was thought to be.
