62 



KNOWLEDGE 



[March, 1902. 



able cases of discontinuous distribution are not wautinfj. 

 Inula salieina, for instance, is sciittcrod ovor the shores and 

 islands of Lout;h Derfj in Irehmd. Tliou<,'h widely s))road 

 in Europe and Asia, it is absent, elsewhere in the British 

 Islands, and furnislies a verv remarkable exainjjle of an 

 outlier of the kind referred to. Cnrex DavaUimii, widely 

 spread in Europe, had its only British station at Hath, but 

 is now extinct there. Cnrex Bu.rbnumii should j)erhaps be 

 reckoned with the relics of the Glacial flora ; with a vast 

 ranjje abroad — Antic and Alpine Europe, Asia, America, 

 and Australia — it is represented in our islands by two 

 patches, one in Scotland (Argyll), one in Ireland (Lough 

 Neagh). Other examples of outlyiiig stations of species 

 ■widespread in Europe are afforded by Buuifhus avsins 

 (Cheddar), Selinum carvifolia (Lincoln and Cambridge), 

 Peiicedanvm officinale (Kent and Essex), Cnicus tuherosus 

 (Wilts), Phyteuma spicafa (Sussex), Teucriiim Bofrys 

 (Surrey), Ilerniaria ciliata (Hants), Epipoyum aphyllum 

 (Hereford). In some of these instances, where the British 

 habitats adjoin the Channel or the North Sea, they may 

 perhaps be looked on as lying on the natural margin or 

 climatic limit of the species ; but in other cases the isola- 

 tion of the stations ajipears to point to a shrinkage in 

 the former area of distribution, and a distinct "island" 

 formation. 



It should be pointed out, however, that a plant-island 

 may mean the very reverse of what has been exemplified 

 above. A recent immigrant which has secured a hold in 

 our country is bound, in the earlier stages of its history, 

 to show a range resembling in its isolation that which has 

 been described as characterizing the older members of the 

 flora. To take an instance. The prickly North American 

 knot-grass. Polygonum sngUtifolhtm, has formed a flourish- 

 ing colony in wild ground in Kerry. The North American 

 orchid Spiranthes Eomanzoffiiana, which till quite recently 

 was in Europe known only in this single station, has a 

 similar colony in the adjoining county of Cork. Both 

 are unknown in Great Britain and elsewhere in Europe. 

 While the latter is regarded by botanists as an extremely 

 ancient native, the former is looked on as probably a 

 recent immigrant. The case of this Polygonum is a 

 particularly difficult one. Usually, the plants introduced 

 through man's agency show a decided aggregation about 

 man's works — towns and harbours and cultivated land ; 

 while the old inhabitants, compared with whom the human 

 tiller of the soil is a late comer, shrink from contact with 

 man, and rejoice in thoroughly wild ground. 



THE MIGRATIONS OF THE SKYLARK AND 

 THE SWALLOW- 



By Harry F. Witherby, f.z.s., m.b.o.u. 



In Knowledge for January, 1901, I called attention to 

 Mr. W. Eagle Clarke's summary of the migrations of the 

 song thrush and white wagtail. The Report of the Migra- 

 tion Committee of the British Association, for 190l, 

 contains summaries, by Mr. Clarke, of the migrational 

 movements in the British Islands of the skylark and the 

 swallow. The facts cleverly elicited and summed up 

 by Mr. Clarke are so important and valuable that they 

 stiould be widely known, and I have attempted below to 

 extract the essence from Mr. Clarke's summaries. The 

 summaries themselves, however, are so condensed in form 

 that every word in them is valuable, and the complete 

 ])aper should be read by those particularly interested in 

 the subject. The committee announce that they are 

 hopeful, in the course of two years more, of giving sum- 

 maries of the movements of all the most representative 



species of migi-ants. It is dillicult to realize the labour 

 involved in unravelling from the mass of facts, collected 

 by means of the schedules supplied to tlie lighthouse 

 keejjers, a coherent and orderly account of the migrations 

 of any single species. But Mr. Clarke, on whom has 

 fallen the entire burden of this work, by long labour and 

 well-considered methods has been most successful, and is 

 much to be congratulated on having traced and set forth 

 very clearly and succinctly the intricate migrations of 

 birds as observed in the British Islands. 



THE SKYLARK. 



The skylark is so common in England all the year 

 round, that few people would suspect it of being a great 

 wanderer. Yet as a migrant, no species makes su great 

 a show in the returns of the light stations, and the 

 complexity of its movements surpasses that of any other 

 British bird. Mr. Clarke has separated these various 

 movements as follows : — 

 In autumn — 



(1) Certain skylarks which have nested heie leave 

 for the south. 



(2) Others come from Central Europe to winter 

 here. 



(3) Others again arrive from Northern Europe to 

 winter in our country. 



(■i) Others pass along our coasts on their way fi-om 



Central Europe to Southern Europe. 

 (5) While others us9 our coasts as a highway on 

 their journey from Northern to Southern 

 Europe. 



In the spring all these movements are reversed. 



In winter, if there is severe weather, many birds leave 

 us, and a number of more or less local movements take 

 place. 



To deal fii-st with the home-bred birds. Although a 

 great many of the skylarks which breed in the British 

 Islands undoubtedly live with us all the year round, great 

 numbers of them are strictly migratory. The emigratioL* 

 of British-bred birds commences almost as soon as the 

 nesting season is over, when skylarks begin to depart from 

 the Hebrides. The migration continues to gain in 

 strength as the autumn advances, and by September and 

 October the skylarks which nested in Scotland and in 

 many parts of Ireland, and the north of England, joiu'ney 

 to the coasts in small bands, and make their way leisurely 

 southward, to winter some in the southern and western 

 counties of England, others on the Continent. During 

 March and April these home-bred birds return. 



Though a considerable number of skylarks thus leave 

 us in autumn, their departure does not materially affect 

 the abundance of the species, since prodigious numbers, 

 from Central and Northern Europe, come to winter here. 

 Indeed, so vast are these numbers, that in November, 

 when most of the migration has ceased, our skylark popu- 

 lation is undoubtedly at its maximum. It must be 

 remembered, however, that at this time cold and want of 

 food has not decimated them, and the skylark being 

 regularly double-brooded, and often rearing even three 

 broods in a season, increases in numbers in a marked 

 degree in autumn from this cause. 



The immigration of skylarks to the British Islands from 

 Central Europe in the autumn is one of the most remark- 

 able movements connected with the migrations of this 

 bird or, perhaps, of any other British bird. It has been 

 laid down as a principle of migration, that birds invariably 

 move southward in autumn and northward in winter, but 



* Tlie terms " oiiiigration " and " iiumignition " here used refer 

 to tlio migration from and to tlie British Islands. 



