OCR Text |
Show 18 ISLAND LIFE. (rAR'l' I. w h1'l e alli'ed speci·e s come t o the north bank, which in tl i·k e manner forms their boundary. As examples we may men IOn that one of the Saki monkeys ( Pithecia monachus?) comes up to the south bank of the Upper Amazon, while immeuiat~ly we cross over to the north bank we find another spectes (p .th · . ,.f:b. b t 2) Among birds · we have the green t ecta 1 uJ" ar a a . . 1 f h jacamar (Galbula viridis), abundant on the north ban r o ~ o Lower Amazon while on the south bank we have two allied species (Galbula rufoviridis and G. cyaneicollis); and among insects we have at Santarem, on the south bank of the Amazon the beautiful blue butterfly, Callithea sapphira, while almost op~osite to it, at Monte-alegre,an allied species, Callithea L epric1,t?'i is alone found. Perhaps the most interesting and best known case of a series of allied species, whose ranges are separate but conterminous is that of the beautiful South American wading birds, called ~rurnpeters, and forming the genus Psophia. There are five species, all found in the Amazon valley,. but each limited to a well-marked district bounded by great nvers. On the north bank of the Amazon there are two species, one in its lower valley extending up to the Rio Negro, and the other in the central part of the valley beyond that river; while to the south of the Amazon there are three, one above the Madeira, one below it, and a third near Para, probably separated from the last by the Tocantins river: Overlapping areas among the species of a genus is a more common phenomenon, and is almost universal where these species are numerous in the same continent. It is, however, exceedingly irregular, so that we often find one species extending over a considerable portion of the area occupied by the genus and including the entire areas of some of the other species. So little has been done to work out accurately the limits of species that it is very difficult to give examples. One of the best is to be found in the genus Dendr03ca, a group of American wood-warblers. These little birds all migrate in the winter into the tropical regions, but in the summer they come north, each having its particular range. Thus, D. dO'l'ninica comes as far as South Carolina, D. c031·ulea to Virginia, JJ. discolor to Southern Maine and Canada; four other species go CHAr . II.] TilE ELEMENTARY FACTS OF DISTIUDUTION. 19 ------------------------ farther north in Canada, while five more extend ·to the borders of the Arctic zone. The species of Tits as. illustrating areas of distrib1.ttion.-In our ?wn hemisphere the overlapping of allied species may be well 1llustrated by the various kinds of titmice, several of which are among our best known English birds. The great titmouse (Par~ts rr:ajoT) has th.e widest range of all, extending from tho Arctic circle to Algena, Palestine, and Persia, and from Ireland right across Siberia t~ the Ochotsk sea, probably following the great northern forest belt. It do~s not extend into China and Japan, where distinct species are found. Next in extent of range is the coal tit ( Parus ater), which inhabits all Europe from the Mediterranean to about 64° N. latitude, in Asia Minor to the Lebanon and Caucasus, and across Siberia to Amoorland. The marsh tit (Parus palustris) inhabits temperate and south Europe from 61 o N. latitude in Norway to Poland and Southwe~ t Russia, and in the south from Spain to Asia Minor. Closely alhed to this-of which it is probably only a variety or subspecies-- is the northern marsh tit (Pants borealis), which overlaps the last in Norway and Sweden, and also in South Russia and the Alps, but extends further north into Lapland and North Russia, and thence probably in a south-easterly direction across Central Asia to North China. Yet another closely-allied species (Pa1·us camtschatlcensis) ranges from North-eastern Russia across Northern Siberia to Lake Baikal and to Hakodadi i~ Japan, thus overlapping Pa1·us borealis in the western portion of its area. Our little favourite, the blue tit (Parus c03rule?,ts) ranges over all Europe from the Arctic circle to the ~iediterranean, and on to Asia Minor and Persia, but does not seem to pass beyond the Ural mountains. Its lovely eastern ally the azure tit (Parus cyaneus) overlaps the range of P. c03rnleus in Western Europe as far as St. Petersburg and Austria, rarely straggling to Denmark, while it stretches all across Central Asia between the latitudes 35o and 56° N. as far a.s the Amoor valley. Besides these wide-ranging species there are several others which are more restricted. Parus teneriffce, a beautiful dark blue form of our blue tit, inhabits North-west Africa and the Canaries; Parus ledouci, closely allied ·to our coal tit, is found only in AlO'eria. 0 ' c 2 |