THE ARCTIC TERN. 713 



colour of upper-parts varies as in Common Tern but dark brown 

 markings are usually closer. There is apparently no constant 

 distinction as some nestlings of Arctic have no dusky on fore -head 

 and some Common Terns have dusky fore-head. 



Juvenile, — As Common Tern but rump and all tail-coverts 

 white, not tinged grey ; tail with more white, usually only 2 or 3 

 outer pairs with gre3 T outer webs ; blackish line on primaries 

 narrow as in adult ; secondaries with more white at tips, outer ones 

 with little grey on inner webs and grey on outer webs considerably 

 paler than in Common Tern ; lesser coverts dark slate -grey, not so 

 blackish as in Common Tern. 



First winter. — Moult and abrasion as in Common Tern after 

 which becomes much like adult winter but can be distinguished by 

 juvenile wings and tail and other retained juvenile feathers. First 



The Arctic Tern {S. paral.smi) hi 1st summer, i.e. one year old. 



summer. — Moult as in Common Tern after which becomes like winter 

 adult Arctic but fore -head and crown often speckled with black 

 (some feathers black or tipped black), under-parts often with a 

 good deal of grey but sometimes entirely white, outer tail-feathers 

 often (but not always) with grey on inner webs at tip and inner tail- 

 feathers usually ash-grey on outer webs ; primaries as adult ; 

 secondaries with less white and slightly darker grey than adult but 

 more white and paler grey than in Common Tern ; lesser coverts 

 slate -grey fringed hoary, paler than in Common Tern.* 



Measurements and structure. — <$ wing 265-282 mm., tail : outer 

 feather 170-200 (one 215), central 70-80, depth of foik 90-138, 

 tarsus 15-17, bill from feathers 30-33 (12 measured). 2 wing 260- 

 275, tail : outer 158-185, central 66-75, fork 92-117. 'juvenile # 

 and $ wing 226-252, tail : outer 105-125, central 65-70, fork 40-55. 

 Primaries : 1st narrow, pointed, and about two -thirds primary 

 coverts, 2nd longest, 3rd 12-22 mm. shorter, 4th 30-45 shorter, 

 5th 55-70 shorter. Best of structure as Common Tern. 



Soft parts. — Bill (ad. winter) blackish, (ad. summer) blood-red, 



* First summer birds with white fore -heads (S. portlandica Ridgway) 

 seem more frequent in this species than in S. hirundo, and this, perhaps, 

 indicates that the latter frequently resemble adults in their first summer. A 

 number of paradisoea in this plumage were noted as breeding by Lord W. Percy 

 in N.E. Siberia in July, 1914 (one shot at nest and other skins in Brit. Mus.), 

 and also by Jourdain in Spitsbergen. — H.F.W. 



