Pastures and fields in Costa Rica have less bird species than forested habitats but there are some special birds that only live in the grass. One of these birds in Costa Rica is the Blue-black Grassquit. A small, common finch never found away from grassy fields the Blue-black Grassquit has some interesting behaviors.
A very small finch, the plumage of the Blue-black Grassquit differs strongly by sex. Like their name says, the male Blue-black Grassquit is a dark, metallic blue bird. When it jumps up, a flash of white at the base of the wings is visible. Two other small, black finches are similar but are dull black and have stronger, larger bills than the Blue-black Grassquit. The female Blue-black Grassquit looks much more like a sparrow with her brownish plumage and streaked underparts. The female Indigo Bunting is similar in plumage but is a lighter brown color and sometimes shows light blue highlights in the tail and wings.
Behavior in Costa Rica
Blue-black Grassquits have the peculiar habit of singing and displaying for long periods of time. The high-pitched, brief insect-like song is similar to a few North American sparrow species that occur in similar habitats. Although Grassquits are not closely related to sparrows, the songs are similar because this type of vocalization carries further in open grassy areas while the brief nature of the song could give predators trouble keying in on these small birds. Each time the Grassquit sings, it jumps straight into the air and opens its wings to reveal white patches. The jump and white in the wings make the males more visible to other Grassquits whose field of view is obscured by the thick vegetation. Females could also be choosing males based on the height of the jump.
Habitat and distribution in Costa Rica
In Costa Rica, the Blue-black Grassquit is dependent upon open grassy fields. About as non-forest as a bird can get, this species will only occur in gardens if there is a large unmowed area. The Blue-black Grassquit jumps and sings from fields throughout Costa Rica, from the lowlands to the Central Valley.