Tropical Tanagers
by Les Beletsky

Excerpted from: Tropical Mexico: The Ecotravellers' Wildlife Guide, Academic Press, 1999.

Tanagers comprise a large New World group of beautifully colored, small passerine birds, most of which are limited to tropical areas. They are among the tropics' most common and visible birds, primarily owing to their habit of associating in mixed-species flocks that gather in the open, often near human habitation, to feed in fruit trees, and they are a treat to watch. All told, there are some 230 species of tanagers (Family Thraupidae), the group including the typical tanagers, the honeycreepers, and the euphonias; about 25 species occur in southern Mexico. Some of the tanagers migrate north or south to breed in temperate areas of North and South America (four breed in the USA, including the WESTERN TANAGER, among the most wildly colored of North American birds). Tanagers inhabit all forested and shrubby areas of the American tropics, over a wide range of elevations, and are particularly numerous in wet forests and forest edge areas. Not devotees of the dark forest interior, they prefer the lighter, upper levels of the forest canopy and more open areas; some prefer low, brushy habitat.

Tanagers vary in length from 9 to 28 cm (3.5 to 11 in), with most concentrated near the smaller end of the range. They are compact birds with fairly short, thick bills and short to medium-long tails. Tanagers' outstanding physical attribute is their bright coloring - they are strikingly marked with patches of color that traverse the entire spectrum, rendering the group among the most fabulously attired of birds. It has been said of the typical tanagers (genus Tangara) that they must "exhaust the color patterns possible on sparrow-sized birds." Yellows, reds, blues and greens predominate, although a relatively few species buck the trend and appear in plain blacks, browns, or grays. The sexes usually look alike. Euphonias are small, stout tanagers, whose appearances, all species being slightly different, revolve around a common theme: blue-black above, with yellow foreheads, breasts, and bellies. Honeycreepers are also usually brilliantly colored.

NATURAL HISTORY

Some tanagers, such as the ant-tanagers, are frequent members of mixed-species flocks (along with antbirds, woodcreepers and others) that spend their days following army ant swarms, feeding on insects that rush from cover at the approach of the devastating ants. Euphonias specialize on mistletoe berries, but eat other fruits and some insects as well. The honeycreepers are tanagers that are specialized for nectar feeding, their bills and tongues modified to punch holes in flower bottoms and suck out nectar; they also feed on some fruits and insects.

Breeding. Most tanagers appear to breed monogamously, although a number of bigamists have been noted (BLUE-GRAY and SCARLET-RUMPED TANAGERS, among them). Breeding is usually concentrated during the transition from dry to wet season, when fruit and insects are most plentiful. In many species, male and female stay paired throughout the year. Males of many species give food to females in nuptial feeding, and during courtship displays make sure that potential mates see their brightly colored patches. Either the female alone or the pair builds a cup nest in a tree or shrub. Two eggs are incubated by the female only for 12 to 18 days and young are fed by both parents for 12 to 18 days prior to their fledging. A pair of tiny euphonias build a nest with a roof and a side entrance, often within a bromeliad plant.

Ecological Interactions. Tanagers, as mashing frugivores, sometimes drop the largest seeds from the fruits they consume before swallowing but, nonetheless, many seeds are ingested; consequently, these birds are active seeds dispersers. Some ecologists believe tanagers to be among the most common dispersers of tropical trees and shrubs, that is, they are responsible for dropping the seeds that grow into the trees and shrubs that populate the areas they inhabit. Euphonias, for example, are crucial for the mistletoe life cycle because, after eating the berries, they deposit their seed-bearing droppings on tree branches, where the seeds germinate, the mistletoe plants starting out there as epiphytes.

Some tanagers and other species of Neotropical songbirds are considered sedentary. That is, they do not migrate or change location much at all. They breed in one place and then stay more or less in the same area during nonbreeding portions of the year. From a conservation viewpoint, sedentary habits are sometimes considered a negative quality. If a species lives in only one habitat type - needs that habitat to survive - then it has little built-in flexibility in its habitat requirements. And should that one habitat be severely reduced, say lowland tropical forest in southern Mexico, then the species may be doomed. But if a species is not sedentary, that is, if it lives during the year in different places and so different habitat types, it has some flexibility in its habitat requirements - which can be both good and bad for conservation. On the one hand, if one habitat is temporarily unavailable, for instance during some seasons of the year, the birds may be able to survive by moving to the other type. On the other hand, to protect a species using two habitats, for instance a high elevation site during breeding and a low elevation site during winter, both kinds of habitats must be preserved. Careful observation of some birds previously thought sedentary indicates that many may actually make some movements during the year. For instance, recent research on COMMON BUSH-TANAGERS near Oaxaca found that although they mostly remain at high elevations, they occasionally move down in winter to low elevation forests.

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