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. In addition to differences in size, plumage varies geographically as well, with southern birds having more brightly coloured plumage. The song consists of clear whistles rendered as hirrJI hirrJI hirrJI, plida plida plida chir chir, etc. The male sings throughout the year, with the frequency of the singing increasing in late winter and reaching a peak in early spring. During the year the male sings the most during the midmorning, but during spring the male sings constantly during mornings and late afternoon. Song is usually delivered from the canopy or other tall trees.

The olive warbler is distributed from the southwestern United States to Nicaragua, making it the only bird family endemic to North America. In the northern part of its range it has a continuous distribution from Yavapai County, Arizona and the southwestern tip of New Mexico along central Mexico to southern Mexico. It has a disjunct distribution across the rest of its range, with populations in Tamaulipas, Coahuila and Sonora and Chihuahua in Mexico, and further south in southwest Guatemala and from northern El Salvador and central Honduras to northern Nicaragua. The olive warbler is a bird of mountains and highlands. In northern areas of its range it occurs from 2,600 m (8,500 ft) above sea level or more, in some parts of its range it may not occur below 3,500 m (11,500 ft). In Oaxaca in Mexico it occupies a range of between 1,700–3,000 m (5,600–9,800 ft) further south in Guatemala it ranges down to 1,850 m (6,070 ft) and at the southern end of its range it can be found as low as 1,000 m (3,300 ft) in Honduras and in Nicaragua it occupies a belt of forest from 1,070–1,370 m (3,510–4,490 ft) . They typically inhabit conifer forests, such as ponderosa and sugar pine forests in Arizona, Abies common fir forests, oak, and pine forests in central Mexico, Guatemala, and Honduras. These forests range from humid to semi-arid. …

The olive warbler is an insectivore, taking insects and other arthropods. No specific information exists about the actual prey species taken, except that they will take the larvae of Tortricidae moths. It forages in forests in the canopy and subcanopy. In feeds in the outer branches and twigs. It mostly feeds in the branches of ponderosa pines, but also feeds in the branches of grey and silverleaf oaks.