Variable Seedeater - Description

Description

The Variable Seedeater is a small, robust bird with a black conical bill. It is 10.5 cm (4 in) long and weighs 11 g (0.4 oz). There are four subspecies, which differ primarily in the plumage of the male:

• S. c. corvina (nominate): Found from southern Mexico and along the Caribbean slope from Belize south to Panama. Adult males are entirely black apart from a small white wing-speculum and white wing linings.
• S. c. hoffmannii: Pacific slope in Costa Rica and Panama. Males resemble males S. c. corvina, but with white half-collar, rump and belly (the rump often intermixed with grey and the flanks retain some black mottling or barring).
• S. c. hicksii: Eastern Panama and adjacent north-western Colombia. Males resemble S. c. hoffmannii, but, except for a small black chin and/or malar, the entire throat is white.
• S. c. ophthalmica: South-western Colombia, western Ecuador, and far north-western Peru. Males are very similar to males of S. c. hicksii, but black malar very fine or lacking, rump purer white, and show purer white flanks with little or no black mottling/barring.

Previously, additional subspecies have been recognized for the various hybrid populations found where the above mentioned subspecies meet (see Taxonomy).

Females are olive-brown above, paler below, and have white wing linings like the male. The racial differences in the female plumages are minor, with S. c. hoffmannii, S. c. hicksii and S. c. ophthalmica generally being paler and less brown than S. c. corvina, and often with a faint yellow tinge below. Juveniles are like the adult female of their subspecies. Males may not acquire the full adult plumage in their first year, and may breed whilst still showing some immature features in their appearance.

A hypermelanic male was reported from Reserva Buenaventura in El Oro Province, Ecuador, in 2005. The bird had increased phaeomelanin; its white areas — except those of the wings — were bright tawny chestnut. A similar bird was collected along the "Pipeline Road" near Gamboa, Panama, in 1963. Such individuals seem to provide a glimpse at the circumstances of speciation: in the genera Sporophila and Oryzoborus, several species exist which differ externally only by one having white areas, the other being hypermelanic just as the two Variable Seedeaters mentioned here. Of course, there must be some factor maintaining reproductive isolation, but the plumage differences between such seedeater species pairs probably had their origin in such a mutation becoming fixed in a founder population due to genetic drift.