During the migration season in spring, and more especially in autumn, these northern river-valleys are frequented by great numbers of land birds on their way to more northern and eastern breeding grounds in Continental areas, or returning south and west to winter in our islands or to cross over them to warmer latitudes. These northern rivers are exceptionally favourable for migration, so many of them trending in the same general direction as the birds are bent on following. Vast numbers of migrant small birds follow such river-valleys as the Tees and the Humber, on their way into Yorkshire, Notts, and Derbyshire, by way of the Don and its tributary streams. It is unnecessary here to dwell upon these species in detail, for we hope to go much deeper into the matter when we come to a study of the migration of birds in the northern shires. We have gathered much evidence in support of this migration during a residence of many years at no great distance from the Humber and certain valleys in direct communication with that important estuary--next, perhaps, in interest, so far as bird-life is concerned, to that still more wonderful locality the Wash, a little lower down the coast.
It is the bird-life of sea and shore especially that renders these northern shires so much more interesting than the littoral counties of the south and west. Compared with these the southern coasts seem tame and deserted, indeed. This is principally due not only to the fact that so many marine species breed in northern areas only, but also to the much greater strength of migration generally along the coasts. All along the coast from Lincolnshire northwards to the Firth of Forth, and onwards to the Hebrides, St. Kilda, the Orkneys and the Shetlands, we have vast and varied bird populations, not only scattered up and down the shore, but congested here and there where the sea-fowl in unnumbered hosts congregate to rear their broods. The southern counties present us with nothing approaching to this; the wealth and variety of the marine avifauna of the northern shires is one of the most pleasing of their many characteristics.
For the sake of comparison we may here state that along the entire coast-line of South Devon--embracing some of the finest cliff scenery in England and full of sandy reaches, rolling downs, rocky islets and stacks, and lengths of shingle and sand--there are but two typical marine species (at most three, if we include the doubtful Oyster-catcher) that breed, and one only of these, the Herring Gull, in any numbers; the other, the Ringed Plover, is local and nowhere numerous! But how very different is the case when we get round the English coast as far as the Wash and enter that area which for the purposes of the present work we describe as the northern shires. Let us follow this line of varied coast, with its alternating lengths of sand and shingle, buttress-like cliffs, rocky shores, and islets round to the Forth, and briefly glance at the several species that frequent it and breed upon it in succession. We will, however, leave for a future chapter the birds that are more strictly confined to the sea-cliffs, and deal with those only that nest either along the flat shores or low rocky islands.