olive birds with gray heads, part 1

May 31, 2005

in Birds, Natural history

Bhvibite“The soft color tones combine to make a most charming picture of pleasing loveliness. He appears to be a well groomed aristocrat among birds.” So Life Histories of North American Birds author Arthur Cleveland Bent described the Blue-headed Vireo (Vireo solitarius), one of my favorite birds. It is the first vireo to arrive here in spring from southern U.S. and Latin American wintering grounds. Not only are these vireos beautiful, but they are feisty, as the little guy working my finger demonstrates (the bird below was a more cooperative). This species was once called the Solitary Vireo, but in 1997 was split into three species: Blue-headed, Cassin’s (V. cassinii) and Plumbeous (V. plumbeous). It is the only eastern vireo to make extensive use of coniferous forests across the northern U.S. and Canada. This may be tied to its early spring arrival, which is prior to the leaf-out of most deciduous trees.

Blue-headed Vireos have an interesting behavior: the males construct “courtship nests.” Although usually rudimentary, they are thought to impress potential mates. These nests Bhviblogare often built in conifers, and tend to be abandoned when breeding nests are built. Male Blue-headed Vireos also help build the breeding nest, and they incubate the eggs as often as the female, behaviors that are unusual among songbirds.

Population trends of Blue-headed Vireos are stable or increasing.  But all is not well in their northern forest homes. An introduced aphid-like insect pest, the Hemlock Woolly Adelgid (Adelges tsugae) is killing hemlocks in forests of the eastern U.S., and it is advancing at a rate of about 15 miles/30 km per year. This Asian insect harms hemlocks by sucking sap from young twigs, thereby retarding growth, and eventually weakening and killing the tree. The biological impact of the destruction of hemlock forests is significant.  This excerpt from a Nature Conservancy document summarizes:

“Hemlock trees are ecologically important and provide a unique environment. T. canadensis is a long-lived conifer, and its stands form a cool, damp habitat with low light levels in the understory. These dense stands possess a very different microclimate and unique species composition from the surrounding, more open forests. These forests are normally stable and resistant to plant invasions. The loss of forests will greatly affect the microclimate and soil conditions. Large-scale hemlock die-off will affect species diversity, vegetation structure, stand environmental conditions, and ecosystem processes.”

AdelgidsThere is currently no way to manage for Hemlock Woolly Adelgid in a forest setting.  Hemlocks can act as keystone species in an ecosystem, and the Blue-headed Vireo is just one of the creatures that relies on the health of hemlock-dominated woodlands.

I hope through good science and with some luck we will find a way to halt the progress of the adelgid. It is hard for me to imagine welcoming spring without the appearance of the Blue-headed Vireo, a special bird, moving through trees just unfurling new leaves, singing its lazy, repetitive song, beguiling me with its pleasing loveliness.

Trix June 1, 2005 at 9:18 pm

I'm going to have to update my field guides. I haven't seen a 'solitary' vireo in two years now; maybe I'll go take a closer look at the hemlocks..

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