The Blue-Gray Tanager (Thraupis episcopus) is one of about 230 species of tropical and subtropical tanagers, and one of the most common and unmistakable birds in Costa Rica. It is a generalist frugavore (fruit-eater), found in a great variety of different habitats, most often in pairs.
It is plentiful and highly visible at Selva Verde, where it regularly frequents bird-feeding trays. Its primary diet comprises succulent fruit from trees, shrubs and vines. Recent studies confirm it has remarkable discriminatory capabilities and can detect 0.09 percent protein variations in food. These tanagers are restless, always on the move. Their call is a raspy squeaky twittering. In flight, they are easy to distinguish because they seem to bounce through the air, alternatively flapping their wings, then gliding with the wings tucked close to the body.
They are extremely social birds. Pairs remain together year-round, often accompanied by adult offspring. As well, many foraging flocks contain unrelated individuals. Blue-gray tanagers are prominent component of mixed-species feeding flocks, some of which contain five or more tanager species. They regularly associate with euphonias, honeycreepers, and several other tanager species.
Although the blue-gray tanager occurs mainly in pairs most of the time, males are notoriously unfaithful partners. Infidelity is rampant and extra-pair liaisons are common. Such behavior has earned males of this species the reputation of being unrepentant bigamists.
These tanagers occupy a huge range, from Mexico to the Amazon Basin. Within that area, local conditions have generated about 15 geographical races.
The blue-gray tanager is about 6 inches long. Pairs make a cup-like nest. The normal clutch is two eggs, incubated for 12-14 days. Family groups often remain intact for several months.
This is undoubtedly one of the easiest birds to see at Selva Verde, owing to its abundance and tameness.
- Robert Alison, PhD
Robert is an avian ecologist and ornithologist based in Victoria, British Columbia. He is a frequent contributor to Field Notes.