are set forth at length in his excellent work, those of Mr. Sclater in _The Ibis_ for 1891, pp. 514-557, and those of Professor Newton in his _Dictionary of Birds_. Many writers would assign to Madagascar a higher rank than that of a Sub-region. MIGRATION.–Few peculiarities of Birds have excited more general interest than their seasonal Migration, which in many species is so marked as to have been observed from very remote times; and it is probable that nearly all species are subject to periodical movements of varying extent. These movements are greatest in the Birds which have their breeding quarters in the northern parts of the Northern Hemisphere; and, with some exceptions, it may be said that the more northerly is the range of a species the more extensive are its migratory wanderings. In the Southern Hemisphere the facts known are as yet insufficient to allow of safe deductions. Absence of a food-supply in winter is alone enough to account for migration in the above cases, and the return from the south in spring is probably due to the desire of Birds to reoccupy their old haunts, or those in which they have been bred. But just as there are some species which habitually breed within the Arctic Circle and winter in the Tropics, there are others which may not go so far in either direction, and yet have their movements governed by exactly the same principle, with the result that in a temperate zone we have Birds coming from the north to winter with us, while others, arriving from the south in spring, spend the summer here, and depart towards autumn. Others again, the true "Birds of Passage," arriving like the last in spring, make little or no stay, but pass onward to more northerly lands, and re-appear for as short a time in autumn on their return journey southwards. Moreover, observation shews that, in most parts of the temperate zone, there are many Birds which, though _resident as species, are migratory as individuals_–that is to say, that while examples of {18}the species may be met with at certain spots throughout the whole year, those which occur at one season are not always the same individuals as those which occur at another–the particular Thrush, Titmouse, or Finch, appearing in the winter not being identical with that which appears in summer. Again, among species of which some individuals are constantly present throughout the year, a great accession to the numbers is made at the close of the breeding-season by the influx of other individuals of the same species bred in another district, though this influx generally lasts for a comparatively short time, and the strangers pass on, accompanied it may be, by some or even most of those that have been reared on the spot in the season immediately preceding. These species are the "Partial Migrants."