NON-INDIGENOUS BRITISH BIRDS. 79 



that, with the series accessible to present description, it 

 is quite unnecessary to repeat their characteristics. The 

 duration of the period of incubation is unknown, but it is 

 probably chiefly performed by the female. 



Diagnostic characters : No character exists by 

 which the eggs of this Ouzel can be separated from 

 those of allied species, and unless thoroughly well 

 authenticated, they are of no scientific value whatever. 



Family TURDID.^. Genus Erithacus. 



Sub-family TURDIN.-E. 



ARCTIC BLUE-THROATED ROBIN. 



Erithacus suecica {Brelwi). 



(British : Abnormal spring and autumn migrant.) 



Single Brooded. Laying season, June. 



Breeding area : Northern Palaearctic region. The 

 Arctic Blue-throated Robin, as its name implies, breeds 

 in the regions lying north of the Arctic circle, from 

 Scandinavia in the west to the Tchuski Land in the 

 east, and in a similar climate at high elevations in 

 more southern areas. Thus it is known to breed in 

 Kamtschatka, as well as on the lofty heights of the 

 Pamirs, and on the Himalayas. 



Breeding habits : The Arctic Blue-throated Robin 

 arrives at its breeding grounds in Scandinavia early in 

 May, but not until the end of the month in Northern 

 Russia, and in Siberia a week or ten days later still. Its 

 favourite breeding grounds and summer haunts are the 

 swampy thickets of birch and willow, the clumps of 



