Olive Warbler

The olive warbler is a medium-sized warbler, 13 to 14 cm (5.1–5.5 in) in length and weighing 9.5 to 12 g (0.34–0.42 oz). It shows clinal variation in size, with more northern populations being larger than southern ones, a phenomenon known as Bergmann's rule. The olive warbler is a long-winged bird. The plumage of the male is mostly grey body with some olive-green on the wings and two white wing bars. The male's head and breast are "tawny-orange", and there is a black patch through the eye. In the female and juvenile, the orange is replaced by yellow, and the black mask is more diffuse.