South American tern

Description

With adult South American terns reaching a length of 40 to 44 centimetres (16 to 17 in),they are larger than either common terns (Sterna hirundo) or Arctic terns (Sterna paradisaea).Otherwise they closely resemble these species in plumage at all times of year.The beak is larger and is red in adults,and they do not have a dark-coloured bar on the carpus of the wing.The black cap extends below the eye,usually separated from it by a white crescent,and the rear edge of the cap is neatly defined.Juveniles have boldly-barred,dusky,upper parts,and retain their barred tertials into their immature plumage,which differentiates them from common and Arctic tern immatures.