OCR Text |
Show ISLAND LIFE. (rAit'l' I. of mammalia. It will be interesting therefore to examine the few cases on record, as we shall thereby obtain additional knowledge of the steps and processes by which the distribution of varieties and species has been brought about. Discontinuity of the Area of Parus palustris.-Mr. Seebohm, who has travelled and collected in Europe, Siberia, and India, and possesses extensive and accurate knowledge of Palrearctic birds, has recently called attention to the varieties and subspecies of the marsh tit (Parus palustris), of which he has examined numerous specimens ranging from England to Japan. I The curious point is that those of Southern Europe and of China are exactly alike, while all over Siberia a very distinct form occurs, the sub-species P. borealis. In Japan and Kamschatka other varieties are found, which have been named respectively P. japonicus and P. camschatlcensis. Now it all depends upon these forms being classed as sub-species or as true species whether thi.s is or is not a case of discontinuous specific distribution. If Parus borealis is a distinct species from Parus palt{;Stris, as it is reckoned in Gray's Hand List of Bi1·ds, and also in Sharpe and Dresser's B'irds of Europe, then Pan&s pah(;stris has a most remarkable discontinuous distribution, as shown in the accompanying map, one portion of its area comprising Central and South Europe and Asia Minor, the other an undefined tract in Northern China, the two portions being thus situated in about the same latitude and having a very similar climate, but with a distance of about 4,000 miles between tb~m. If, however, these two forms are reckoned as sub-species only, then the area of the species becomes continuous, while only one of its varieties or sub-species has a discontinuous area. It is a curious fact that P. pah&stris and P. borealis are found together in Southern Scandinavia and in some parts of Central Europe, and are said to differ somewhat in their note and their habits, as well as in colouration. Discontinuity of Emberiza schmniclus.-The other case is that of our reed bunting (Embe,riza schmniclus), which ranges over almost all Europe and Western Asia as far as the Yenesai valley and North-west India. It is then replaced by another smaller 1 See Ibis, 1879, p. 32. |