Elfin-woods Warbler

Appearance

The elfin woods warbler is a small passerine, averaging 12.5 cm (5 in) in length and 8.4 g (0.30 oz) in weight.[9] Its upperparts are predominantly black with white areas, and its underparts are white with black streaks. Other identifying characteristics are dark brown eyes, white patches on its ears and neck, an incomplete white eyering, a white eyestripe, and two white spots on its outer tail feathers. Like other Antillean warblers (Adelaide's warbler, Saint Lucia warbler, plumbeous warbler, and arrowhead warbler), it has a long bill and short, round wings (53.8 mm or 2.12 in average). Among Setophaga species, only Adelaide's warbler has a shorter average wing length. Juveniles differ from adults, retaining a grayish-green back for approximately a year and partially molting from July to October.

Naming

The species name, angelae, is a tribute to Angela Kepler, one of its discoverers.

Distribution

When first discovered, the elfin woods warbler was believed to exclusively occur in the high elevation, from 640 to 1,030 meters (2,100 to 3,380 ft), dwarf or elfin forests of the El Yunque National Forest in eastern Puerto Rico. The wind-clipped trees in these forests rarely exceed 5 meters (16 ft) in height and are characterized by stiff, thick twigs, leathery leaves and impenetrable, dense undergrowth ideal for hiding from predators. Later studies showed that the species migrated to lower elevations, between 370 and 600 meters (1,210 and 1,970 ft), in Tabonuco and Palo Colorado forests. Three more populations were discovered in the Maricao State Forest (1972, largest known population), the Carite State Forest (1977) and the Toro Negro State Forest (late 1970s).

The species is presumed extirpated from two locales, occurring only at El Yunque National Forest and the Maricao State Forest. The elfin forest at El Yunque National Forest is characterized by high rainfall and humidity, low temperatures and insolation, and constant winds. It is found at mountain summits and is primarily composed of dense shrub and small trees with moss and epiphyte growth in its plants and floor. The species richness is low when compared to other types of forests (tabonuco, palo Colorado and palma sierra forests) found in the Luquillo Mountains. The elfin forest at the Maricao State Forest, located in western Puerto Rico, receives an annual average rainfall of 2,250 millimeters (90 in), a high amount considering that a rainforest, by definition, receives a minimum of 1,700 millimeters (67 in) annually. Since its soil has low water-holding capacity its vegetation is more xeric than expected. The species's highest density occurs in Podocarpus forests in the Maricao State Forest. Little information is available on the elfin forests at Toro Negro and Carite.

Status

Due to its small populations and restricted habitats, conservation efforts were begun in 1982 to protect this species, but as of 2005, the warbler was still in need of protection. The species is not in immediate danger as the majority of its habitat is protected forest, but introduced species (such as rats and small Asian mongooses), habitat reduction, and natural disasters represent potential threats to the population.

Reproduction

The elfin woods warbler breeds from March to June. Both parents are involved in the construction of the nest and in feeding the chicks. Nests are built close to the tree trunk within dry aerial leaf litter, usually Cecropia leaves (a material used by no other Parulidae species), in Bulbophyllum wadsworthii trees. Nests are well-concealed and located 1.3 to 7.6 meters (4.3 to 24.9 ft) above ground level. In 2003 a nest with four chicks was found inside a tree stump of Colorado tree, Cyrilla racemiflora, at Maricao. The nest was at about 15 feet above ground level, with little cover in a secondary forest area. Nests are cup-shaped and made from small roots and twigs, dry leaves of Chusquea abietifolia and B. wadsworthii, and dry Panicum maximum leaves. The interior is made from fibers of C. abietifolia, dry leaves and other plant matter. Females lay two or three white eggs with red-brown spots. The chick's diet consists of insects—parents have been observed offering lepidopteran and orthopteran adults and lepidopteran larvae to hatchlings.

Food

These birds are insectivores, as they feed by gleaning small insects off the habitat leaves.