688 A PRACTICAL HANDBOOK OF BRITISH BIRDS. 



mantle black-brown, feathers very narrowly tipped pale brown and 

 dark grey central portions not entirely concealed ; lower-mantle 

 and scapulars showing more grey, with paler brown tips and 

 broader whitish extreme tips ; back paler with very faint brownish 

 tips ; upper tail-coverts tipped hoary sometimes with brown tinge ; 

 under -parts white with dark brown patch on each side of upper- 

 breast ; under wing-coverts and axillaries white ; tail-feathers as 

 adult but brownish at tips ; primaries and secondaries as adult but 

 shafts of primaries usually brown, not white ; innermost secondaries 

 and greater and median coverts tipped brown as scapulars, rest of 

 coverts with small brown tips ; lesser coverts blackish with very 

 narrow hoary fringes. 



First winter. — No certain examples and none in moult examined 

 but appears to become like adult winter, probably by moult of body- 

 feathers and by wear of tips of wing-coverts. First summer. — Birds 

 moulting in May and June may be first summer and apparently 

 they do not become so uniformly dark on under-parts as 

 adults. 



Measurements and structure. — <J wing 206-220 mm., tail : 

 outer feather 78-86, central 60-66, depth of fork 14-22, tarsus 15-17, 

 bill from feathers 27-28 (12 measured). $ wing 200-218. Primaries : 

 1st pointed, narrow and about two-thirds primary-coverts, 2nd 

 longest, 3rd 8-15 mm. shorter, 4th 20-32 shorter, 5th 36-50 shorter ; 



outer web of outer pri- 

 mary very narrow. Outer 

 secondaries shorter than 

 inner primaries, inner 

 ones about as long as 8th 

 or 9th primary, outer 

 webs sloped off at tips. 

 Tail forked, 12 feathers, 

 tips of outer rather 

 T Ti ^v\ sharply pointed, but 



rounder and shorter in 

 juvenile. About half tibia 



Feet of the Black Tern (left) and the Common Tern (right) K QTA t QrqiK olpnrlpr anrl 

 to show difference in webbing. Dare > ^arSUS Sienaer ana 



short, toes longer, three 

 front ones connected by deeply concave webs, hind toe free, claws 

 slender, long, and very little curved. Bill slender, much com- 

 pressed, upper mandible slightly arched and very slightly longer 

 than lower, gonys rather long and gently sloped off to tip, which 

 is very sharp. Nostril basal, slit-like. 



Soft parts. — Bill black (juv. brown-black with base of lower 

 mandible dark yellow) ; legs and feet dark red-brown (juv. deep 

 yellow) ; iris dark brown. 



Characters and allied forms. — C. n. surinamensis (America) is 

 distinctly darker in summer on upper and under-parts and slightly 

 darker on rump in winter and juvenile. Distinguished from other 



