This order, the Passeriformes, is also called 'perching birds' because all members have a foot with three toes pointed forward and one long toe pointing backward, making a elaw suitable for perching on twigs. The passerines also share other anatomical features as well as a unique type of sperm.
This is the largest, most recently evolved, and most taxonomically confusing order of birds, and ornithologists are constantly changing the names and relationships of the species, sometimes splitting one species into two or more, sometimes lumping two to make one, and sometimes moving them into a different family.
About half of Costa Rica's birds are passerines, ineluding, among others, the families of flycatchers (78 species), antbirds (30 species), wrens (22 species), ovenbirds (18 species), woodcreepers (16 species), and the huge catchall Emberizidae family, which ineludes the warblers (52 species, ineluding many North American migrants), tanagers (50 species), blackbirds (20 species), and a confusing array of over 50 sparrows, finches, and grosbeaks. Some, like the woodcreepers, are so similar to one another that ornithologists cannot reliably identify them unless they catch the birds. Others, like some tanagers and cotingas, are so extravagantly and uniquely plumaged that identification is very easy. It is some of the latter that I discuss here.
Tanagers are fairly small but often very colorful birds that mainly live in the Neotropics. The most abundant, and one of the country's most common birds, is the blue-gray tanager (tangara azuleja; Thraupis episcopus). Its head and body are a pale blue gray that becomes brighter blue on the wings and tail. It prefers open, humid areas and is seen up to 2300m everywhere except the dry northwest and deep inside the forest.
The male scarlet-rumped tanager (tangara lomiescarlata; Ramphocelus passerinii) is jet black with a bright scarlet rump and lower back, a flashy and unmistakable combination. This bird is common in the Caribbean and southern Pacific slopes. The females, which travel with the males, are a varied mixture of olive, orange, and gray and look like a different species. Both, however, have a silvery bill, found on the Caribbean slope, and the yellow-billed cotinga (cotinga piquiamarillo; Carpodectes antoniae), found on the south Pacific slope. In both cases, the female is a pale gray.
The blue ones, both with a purple throat and belly, are uncommon though unmistakable if seen. The lovely cotinga (Cotinga amablis) is found on the Caribbean and the turquoise cotinga (Cotinga ridgwayi) is in the south Pacific lowlands. One of the strangest cotingas is the three-wattled bellbird (pájaro campano; Procnias tricarunculata).
The 46cm-long white-throated magpie jay (urraca; Calocitta formosa) is blue above and white below and on the face, with a very long tail and a crest of forward-curling, black-tipped feathers. It is often seen in the drier northwest slopes and the Península de Nicoya. The slightly smaller brown jay (piapia; Cyanocorax morio) is mainly brown with creamy outer tail feathers and belly. It is found in deforested areas. Jays are noisy birds with harsh calls.
The colonial Montezuma oropendola (oropéndola de Moctezuma; Psarocolius Montezuma) weaves a large sacklike nest, sometimes over a meter in length. Colonies of these nests are often seen hanging from branches of tall trees in open areas of the Caribbean lowlands. It has a chestnut-colored body, black head and neck, and golden-yellow outer tail feathers that are conspicuous in flight. The dark bill is orange-tipped and there is a bluish patch on the face.
The less-common chestnut-headed oropendola (Psarocolius wag/eri) builds similar nests and has yellow tail feathers, but is black with a chestnut head and pale yellow bill. Both are found mainly on the Caribbean slope and occasionally elsewhere. Their calls are varied, loud, gurgling, and at times mechanical sounding.
Costa Rican cotingas flaunt their colors. Two are shining white and two others are a brilliant blue and purple. The white ones are the snowy cotinga (cotinga nivosa; Carpodectes nitidus).