olive birds with gray heads, part 2

June 6, 2005

in Birds, Natural history

Tewablog1 Some years I don’t catch many Tennessee Warblers (Vermivora peregrina), but this year seemed to be a good year for them.  Their populations surge and wane with outbreaks of spruce budworms (Choristoneura fumiferana) on their northern nesting grounds. The budworms tend to be cyclical, and Tennessee Warblers are one of a suite of warblers that are considered spruce budworm specialists; others include Cape May Warbler (Dendroica tigrina) and Bay-breasted Warbler (D. castenea).  During budworm outbreaks, Tennessee Warblers will increase their clutch size — laying up to eight eggs rather than three or four — and occur at higher densities in response to this abundant prey.

Tennessee Warblers winter from Mexico to Venezuela, often on shade coffee plantations. Trees in the genus Inga are common overstory trees in coffee plantations, and important to wintering Tennessee Warblers. In addition to eating insects, the warblers are nectar thieves, stealing nectar from the flowers by piercing the base of the blossom, thus getting away with the goods without pollinating the plant.  The birds also utilize other tree and shrub species in winter and during migration in the more conventional, stick-your-head-in-the-flower manner.  Their faces, then, may become stained with red or orange pollen.

The majority of Tennessee Warblers, 97%, breed in Canada’s boreal forests.  In fact, according to the Boreal Songbird Initiative:

  • 53% of warbler species, 80% of the waterfowl species of North America, and 63% of the finch species breed in the boreal region.
  • For nearly 100 species, 50% or more of their entire breeding populations occur in the Boreal.
  • Over 80% of the North American populations of 35 species occur in the Boreal.

The boreal forests are so crucial to so many of the breeding birds of North America that several organizations have begun working on education, advocacy, and conservation for the region.  In addition to the aforementioned Boreal Songbird Initiative, there is NDRC’s Heart of the Boreal Forest, and the Boreal Forest Network.  All take donations!  The public can also help by purchasing paper products that are not made from wood harvested from boreal forests.

Likewise, many of our North American breeding birds are dependent on shade-grown coffee plantations, so you can also help by drinking shade-grown coffee.

When Tennessee Warblers pass though my neck of the woods, I am totally immersed in the richness and promise of a Midwestern spring.  Tropical coffee plantations and northern boreal forests seem distant, but this little olive bird with a gray head is a perfect representative of both of these habitats, and reminds me how important they are to the continued spectacle of migration.

Olive birds with gray head, part 1 here.

GrrlScientist June 7, 2005 at 7:44 am

Excellent message! I have been talking for a month or more about birds that depend upon the boreal for some or all of their life cycle, and I am happy to see someone else talking about it too. Including information about shade-grown coffee makes this message even better!

Rurality June 7, 2005 at 11:39 am

I hadn't noticed TN warblers with orange heads before, but have seen plenty of newly-arrived migrating prothonotaries looking like that!

Love your blog.


Trix June 11, 2005 at 8:21 am

Thanks for mentioning the Boreal Songbird Initiative; they're site is great, they're cause is great, and bird's plight is great!

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