Great-billed seed finch
The great-billed seed finch is a species of bird in the family Thraupidae. Its natural habitats are subtropical or tropical moist shrubland, swamps, and heavily degraded former forest. They are found in two separate general populations, one in the northern Amazon rainforest and the other in the Cerrado. They live in flooded areas with nests low to the ground. The adults express strong sexual dimorphism. Males are black with white under wing-coverts and ivory white bills, and the females are generally light brown with white under wing-coverts and black bills. Both the male and female have very large, thick bills. The great-billed seed finch has a melodious call, which has made it a target for trapping.
Although the population is quickly declining due to trapping and loss of habitat, not much is known about its behavior and ecology.
Taxonomy
The great-billed seed finch was called Fringilla crassirostris when a female was collected on the eastern coast of Brazil in 1815 by Prince Maximilian of Wied-Neuwied. Twenty years after his description was published, the seed finch was included in the newly proposed genus Oryzoborus by Jean Louis Cabanis.The seed finches were once categorized in the genus Oryzoborus. They are a group of six species: the chestnut-bellied seed finch, large-billed seed finch, black-billed seed finch, thick-billed seed finch, great-billed seed finch, and the Nicaraguan seed finch. The females of seed finches are very similar in morphology. The taxonomy is therefore almost exclusively based on the male plumages. Categorization of the seed finches had been historically based on male plumage patterning with color groups such as gray and chestnut-colored. Further molecular and morphological analyses of the birds led to the genus Oryzoborus being subsumed into the genus Sporophila.
The great-billed seed finch includes two subspecies:
- S. m. maximiliani which is found mainly in Cerrado, eastern Bolivia, and in the Brazilian states of Goiás, Bahia, Minas Gerais, Espirito Santo, São Paulo, Mato Grosso, and Mato Grosso do Sul.
- S. m. parkesi which is found in southeastern Sucre to Elta Amacuro, northern South America, eastern Venezuela, northern Bolivia, western Guyana, and the northernmost part of Brazil.
Description
The great-billed seed finch is sexually dimorphic. They have an extremely large and thick bill, that is chalky white in males and black in females. The beak volume is about 840mm³. The males are black with white or white and black under wing-coverts. The females have a warm brown back and a buffy brown belly with white under wing-coverts. The females are very similar to other adult females of the Sporophila genus. Both the male and female great-billed seed finch are very similar in appearance to the male and female large-billed seed finch. It is a medium-sized finch at around in length. The juvenile is similar in appearance to the female. Sexual dimorphism presents itself in males when they begin to sing. The male juvenile eventually moults its black feathers, having a patchy appearance for several months until it is fully black.Due to their similarity with other species, sexual dimorphism, and juvenile appearance, great-billed seed finches can be very difficult to identify morphologically.
The eggs of the great-billed seed finch are grayish white with black blotches and light brown spots.
Distribution and habitat
The great-billed seed finch exists in two separate populations in South America. The southern population is found in the Cerrado and in the Cerrado enclaves into the transition zones in Atlantic Forest. The northern population is found in the northern Amazon rainforest.The great-billed seed finch is specialized to live in humid environments and is often associated with flooded areas and marshy borders.