GENERAL CONSIDERATIONS 537 



goose {Branta nigricans), and grey plover {Squatorola helvetica). These 

 birds are in the same category as the previously named group. 



The following species are partial migrants, being resident in 

 Britain at all seasons, but having migratory representatives which 

 visit Britain in summer, and which winter somewhere to the south : 

 linnet {Linota cannabina), twite {Linota flavirostris), redbreast (Erith- 

 acus rubecula), and teal [Nettion crecca). The following, which have 

 also failed to establish themselves, are partial residents, but are also 

 largely winter visitors in Britain: gadwall {Chaulelasmus streperus), 

 pintail (Dafila acuta), wigeon {Mareca penelope), pochard (Nyroca 

 ferina), and golden plover (Charadritis pluvialis). 



As several writers on the subject of migration have pointed out, 

 racial forms of certain species appear regularly in Britain, either as 

 seasonal visitors or as occasional guests, and these include species of 

 which resident representatives occur all the year round. Again in 

 catching birds for exportation, it is impossible for the professional 

 bird-catcher to ascertain whether the specimens captured belong to 

 residents or to migrant races. The probabilities seem to me to be 

 that they mostly belong to the latter, because the bird-catcher goes 

 where he knows or expects to find birds gathered together in flocks, 

 and these mostly come together preparatory to migration. It is quite 

 possible that the specimens of linnets and twites brought to this 

 country were migratory representatives of these species; this may 

 explain their failure to remain here. The following birds, all of which 

 have become naturaHsed in New Zealand, are also resident in Britain 

 all the year round, but it is well known that there are numerous 

 migratory races of them: rook {Corvus frugilegus), stariing {Sturnus 

 vulgaris), goldfinch (Carduelis elegans), greenfinch {Ligurinus chloris), 

 skylark (Alauda arvensis), song thrush (Turdus musicus), hedge-sparrow 

 {Accentor modularis). Mallard {Anas boscas). In a note to his list of 

 partial migrants, Clarke states that : " Starlings marked in Britain have 

 been recovered in France, Greenfinches in France, Linnets in France, 

 Song Thrushes in France and Portugal, and Mallard and Teal in 

 Germany." Seebohm also (in Siberia in Europe, p. 245) says: 



Many birds, such as the Robin, the Blackbird, the Song Thrush, etc., 

 which are resident in England, are migratory in Germany. There is every 

 probability that it is only within comparatively recent times that these 

 birds have ceased to migrate in England, and we may fairly conjecture 

 that should the English climate remain long enough favourable to the 

 •winter residence of these birds, they will develop into local races, which 

 will eventually have rounder and shorter wings than their Continental allies. 



In connection with the naturalisation of the rabbit, it is interesting 

 to note that the earlier introductions all failed to establish themselves 



