16 BRITISH BIRDS. 
FALCO GYRFALCO ann FALCO CANDICANS. 
BROWN JER-FALCON and WHITE JER-FALCON. 
(PLATE 3.) 
There are two species of Jer-Falcons, very distinct from each other, and 
having well-defined geographical ranges, but connected together by a series 
of intermediate forms in the intermediate localities. It is not known that 
these intermediate forms are produced by the interbreeding of the two 
extremes; but in the case of the form which inhabits Iceland there seems 
to be evidence that some interbreeding does take place (see Ibis, 1862, 
p. 47, footnote). The synonymy of the two species and their most im- 
portant intermediate forms is as follows :— 
FALCO GYRFALCO. 
Brown JER-FALCON. 
Falco gyrfalco, Linn. Syst. Nat. i. p. 150 (1766); et auctorum plurimorum— 
Schlegel, Bonaparte, Naumann, Gould, (Sharpe), &e. 
Falco sacer, Briss. apud Forst. Phil. Trans. Roy. Soc. \xii. p. 882 (1772). 
Falco lanarius, Linn. apud Lath. Gen. Syn. Suppl. i. p. 282 (1787). 
Falco sacer, var. 8, Gmel, Syst. Nat. i. p. 273 (1788, ex Forst.). 
Hierofalco gyrfaleo (Linn.), Brehm, Journ. Orn. 1853, p. 266. 
Falco norvegicus, Tristr. Ibis, 1859, p. 24 (ex Wolley’s Sale Cat. nee Lath.) 
Falco gyrfalco norwegicus, Schl. Mus. Pays-Bas, ii. Falcones, p. 12 (1862, nee Lath.). 
Falco (Hierofaleo) gyrfaleo (Linn.), var. gyrfaleo (Linn.), Ridgw. N. Amer. Birds, 
iii. p. 108 (1874). 
Falco (Hierofalco) gyrfaleo (Linn.), var. sacer (Forst.), Ridgw. N. Amer. Birds, iii. 
p. 115 (1874). 
FALCO GYRFALCO-CANDICANS. 
IcELAND JER-F acon. 
Accipiter falco islandicus, Briss. Orn. i. p. 336 (1760). 
Accipiter gyrfalco islandicus, Briss. Orn. i. p. 373 (1760). 
Falco islandus, Gmel. Syst. Nat. i. p. 271 (1788, ex Briinn. nec Lath.). 
Hierofalco islandus (Gmel.), Sharpe, Cat. Birds Brit. Mus, i. p. 414 (1874, nee Lath.). 
FALCO CANDICANS-GYRFALCO. 
SouTH-GREENLAND JER-FALcon, 
Falco rusticolus, Linn, Syst. Nat. i. p. 125 (1766). 
Falco fuscus, Faber, Faun. Groenl. p. 59 (1780). 
Falco arcticus, Holb. Zeischr. Ges. Nat. iii. p. 426 (1854), 
Falco gyrfalco groenlandicus, Sch/. Mus. Pays-Bas, ii. Falcones, p. 13 (1862). 
Falco holbeelli, Sharpe, Proc. Zool. Soc. 1873, p. 415. 
Hierofalco holboelli (Sharpe), Sharpe, Cat. Birds Brit. Mus. i. p. 415, pl. xiii, (1874), 
