66 A PEACTICAL HANDBOOK OF BRITISH BIRDS. 



Measurements and structure. — $ wing 398^15 mm., tail 195-225, 

 tarsus 55-65, bill from base of feathers 30-38 (18 measured). 

 $■ wing 425-460 mm. Primaries : 3rd longest, 2nd and 4th occa- 

 sionally as long but usually 5-10 mm. shorter, 1st and 5th 35-50 

 shorter ; 2nd to 4th emarginated on outer webs ; outer edge of 

 1st primary and of emarginated portions of 2nd to 4th with very 

 short serrations. Outer secondaries about as long as 10th primary, 

 rest becoming longer and longest about equal to 7th primary, 

 tips rounded. Tail slightly rounded, 12 feathers, tips rounded. 

 Under tail -coverts nearly as long as tail. Tarsus and toes thickly 

 covered with feathers (with long, thread-like rami), three toes directed 

 forwards and one backwards, claws long, much compressed, very 

 strong, curved and tapering to very sharp point. Bill short, very 

 strong and much compressed, upper mandible strongly curved 

 and projecting at tip which is sharply pointed, lower mandible 

 broader and shorter with rounded tip. Nostrils covered by bristle- 

 like feathers of disk. 



Soft parts. — Bill and claws blackish horn-colour ; iris golden. 



Characters. — No subspecies. Large size and white coloration 

 with or without brown bars easily distinguish it. 



Breeding-habits. — Makes no nest, but lays eggs in depression on 

 hillock in tundra or high fjeld. During lemming years accompanies 

 hordes of migrating rodents, breeding far south of its usual limits. 

 Eggs. — From 4 to 9 or 10, white, and in some cases at any rate laid at 

 considerable intervals, incubated eggs and half grown young having 

 been found together. Average of 100 eggs, 57.3x45.1. Max.: 

 63 X 46.5 and 60.3 X 48.4 Min. : 51 .5 x 43.7 and 55 x 42. Breeding- 

 season. — Varies according to latitude from mid-April and May to 

 June. Incubation. — By hen only, male keeping guard. Period 

 about 32 days. Normally single brooded, but possibly some birds 

 do not breed every year. 



Food. — In British Isles feeds on rabbits, mice, birds (Duck, Little 

 Grebe, Partridge and small birds, such as Buntings and Pinches) 

 and insects (beetles), as well as spiders (found in castings). Li 

 Arctic regions feeds on lemmings, Arctic hare and birds (Little Auk, 

 Ducks, Ptarmigan, Gulls and small birds). It has even been known 

 to attack a wounded Brent Goose and catches fish at times. 



Distribution. — British Isles. — Almost regular winter-visitor to 

 Shetlands and frequent Orkneys and Hebrides, often on mainland 

 of Scotland and in Ireland, where about forty recorded, chiefly 

 in north and north-west, and most numerously Mayo. In England 

 three taken in Northumberland, one and several seen Yorks., one 

 Derby., ten Norfolk, one Suffolk, one seen Bucks., about five Devon, 

 one Somerset, one Scilly Isles. Occurs from Sept. to April, one 

 (Elgin) June 18. 1917, one (Mayo) July 21, 1906, one (Bucks.) 

 July-Aug., 1912. 



