NON-INDIGENOUS BRITISH BIRDS. 125 



Average measurement, 2*3 inches in length by i'8 inch 

 in breadth. Incubation (often begun as soon as the 

 first ^^^ is laid) is apparently performed chiefly by the 

 female, but the duration of the period is unknown. 



Diagnostic characters : 1 know of no character 

 which will serve to distinguish the eggs of this Falcon 

 from those of the other Jer-Falcons. As a rule the 

 locality is of the first importance in their identification. 

 From eggs of the Peregrine they may be distinguished 

 by their larger size, more ovate form, coarser grain, and 

 on an average orange-brown instead of reddish-brown 

 colour. 



Family FALCONID.E. Genus Hierofalco. 



Sub-family FALCONING. 



ICELAND JER-FALCON. 



Hierofalco islandus {Gmcli?i). 



(British : Rare nomadic winter migrant.) 



Single Brooded. Laying season, middle of April to 

 middle of May. 



Breeding area : Extreme North-western Pal^arctic 

 region. The Iceland Jer-Falcon appears only to breed 

 in Iceland. 



Breeding habits : Although great numbers of eggs 

 of the Iceland Jer-Falcon have been collected, the 

 nesting habits of the bird itself are little known. Its 

 favourite and apparently only nesting places are on the 

 cliffs and crags that bound the sea-coast, or that hem in 

 the inland lakes and fjords. This Falcon is not known 

 to make any nest, beyond a mere hollow in the scanty 

 soil on a ledge or shelf of the cliffs, but it is said 



