104 A PRACTICAL HANDBOOK OF BRITISH BIRDS. 



various varieties were brought to Denmark by the Icelanders. From 

 Kerr — 1792 — onwards islandus has generally been restricted to the grey- 

 backed Iceland form). 

 Falco islandus J. F. Gmelin, Yarrell, I, p. 46 (part) ; Saunders, p. 343. 



Description. — Adult male and female. Winter and summer. — 

 Occasionally very difficult to distinguish from F. r. rusticolus, 

 crown being only slightly more streaked with whitish, nape rather 

 whiter and rest of upper -parts with paler slate-grey bars. Usually 

 crown creamy -white streaked black-brown, nape white with irregular 

 black-brown markings, rest of upper -parts and tail with ashy- 

 grey bars much paler than in F. r . rusticolus, ear-coverts and cheeks 

 white streaked black-brown, under-parts as in F. r. rusticolus, but 

 often with finer black streaks and smaller spots. This plumage 

 is acquired by complete moult from June to January. 



Nestling. — (Not examined.) 



Juvenile. — Sometimes like that of F. r. rusticolus, but usually 

 crown and nape with considerably more white, being usually white 

 thickly streaked dark brown ; feathers of mantle, scapulars and 

 wing-coverts usually with whiter edgings ; upper tail-coverts with 

 more definite whitish bars ; tail-feathers also more definitely barred 

 white ; ear -coverts and cheeks usually with more white ; comb- 

 like barring on inner webs of primaries whiter. 



First winter. — Like juvenile. First summer.— The juvenile 

 plumage is completely moulted from June (sometimes almost 

 complete by July, when bird is about a year old) to January. New 

 plumage like that of adult. 



Measurements and structure. — (J wing 366-380 mm., tail 190- 

 210, tarsus 57-69, bill from cere 23-27 (11 adults measured). $ 

 wing 410-430, bill 26-29 (12 adults measured). Primaries : 2nd 

 longest, 1st 12-17 mm. shorter, 3rd 8-12 shorter, 4th 25-30 shorter, 

 5th 45-55 shorter ; 2nd and 3rd emarginated outer webs, 1st very 

 abruptly emarginated and attenuated near tip of inner web and 

 2nd not so abruptly. Rest of structure as Peregrine Falcon. 



Soft parts. — Bill bluish-horn, darker at tip, yellowish at base ; 

 cere, legs and feet yellow in adult, grey in young ; iris dark brown. 



Breeding-habits. — Necessarily cliff -breeder only. Nest.— Hantzsch 

 describes it as flat and broad, with a few twigs and hard stalks. 

 Eggs. — Normally 4, but good many instances of 5 (and even 6) 

 on record, and 3 not uncommon, especially in second layings. 

 Somewhat lighter in colouring than Gyr -Falcons' in a series but 

 often indistinguishable, frequently showing good deal of light 

 ground : exceptionally quite white. Average of 100 eggs, 59.1 X 

 46.38. Max. : 64 x 48.2 and 60.1 X 49.3. Min. : 53.8 X 44.2 

 and 57.5 X 41.8. Breeding -seas on. — Eggs laid from end April 

 to mid-May. Incubation. — Chiefly by female, but Faber asserts 

 male takes a share. Period probably not less than four weeks, 

 and young leave nest in first half July. Single brooded, but will 

 lay again if first clutch is taken. 



