Know your coffee birds: Tennessee Warbler

The Tennessee Warbler (Vermivora peregrina) is a great example of a "Neotropical migrant": a bird that breeds in North America and winters in the tropics. They can be common to abundant during migration over a wide swath of the continent (including Tennessee, where it was discovered, resulting in the rather inappropriate name). Tennessee Warblers are one of the classic winter residents of shade coffee farms in Central America and northern South America, which led tropical ornithologist Alexander Skutch to conclude that they really should be named "Coffee Warbler."

A Tennessee Warbler in winter in Costa Rica's Central Highlands.

Tennessee Warblers nest across the Canadian boreal forest. They are one of the warblers that specialize in spruce budworms. In years when these insects are abundant, populations of the warbler swell. In fact, Tennessee Warblers are one of the most important predators of these devastating pests.

Range map. Click to enlarge.

On their wintering grounds, Tennessee Warblers like semi-open to open second growth forest, and shade coffee plantations share the habitat characteristics of these forests. On coffee farms, Tennessee Warblers are often associated with flowering trees, especially those in the genus Inga, which are very common on shade coffee farms. Although the warblers may defend a flowering tree, they are also often found in mixed species flocks. Since Ingas do not flower for a long period of time, these flocks may track the flowering trees across the landscape. The warblers also fond of  two other tree genera frequently used as shade trees on coffee farms, Erythrina and Grevillea.

Why do the warblers like the flowering trees? Winter is dry season in the tropics, when insects are less abundant. Nectar becomes and important part of the winter diet of Tennessee Warblers. For this reason, shade coffee farms are considered very important to the survival of this little bird with the understated colors and loud, ringing voice.

Read more:

• The Coffee Warbler (Smithsonian Migratory Bird Center, by my friend Tom Dietsch.
• Tennessee Warbler (Boreal Songbird Initiative)

Photo of Tennessee Warbler by Jerry Oldenhettel.
Range map from All About Birds, Cornell Lab of Ornithology.

Comments

[Georgia]

Writing to let you now about a research short published in Cornell's Birdscope (22:3 Summer 2008) about the effect of "tropical urbanization" on neotropical migrants.