From Opus

Photo by DarrenMcKenna.
Police Point Park, Medicine Hat, Alberta, Canada

Vireo gilvus

[edit] Identification

L. 13cm, W. 22cm
A drab vireo with few distinguishing marks; warbling song is the best clue. There is an indistinct stripe over the (black) eye. Upper parts are gray or olive-gray, breast whitish with light yellow wash on flanks. Blue-gray legs and feet.

Easternmost and westernmost birds are quite different: eastern bird averages longer, deeper bill (looks a little swollen) with paler upper mandible, longer wing, and heavier. In plumage, the crown of western birds often darker than rest of upperparts, which has a generally stronger olive-green tone than eastern birds. Differences in plumage appears stronger between eastern and north-western birds and less pronounced when comparing with south-western birds.

[edit] Distribution

Throughout the USA except the deep south, in the western provinces of Canada and extreme western mainland of Mexico. Has declined in the eastern U.S. where shade trees have been sprayed with insecticides.

[edit] Taxonomy

[edit] Subspecies

Warbling vireo has a total of six recognized subspecies^[1]:

• V. g. gilvus:

• South-western Canada to east-central US; winters to north-eastern Costa Rica

• V. g. swainsoni:

• South-eastern Alaska to north-western Baja; winters to El Salvador

• V. g. victoriae:

• Mountains of southern Baja California (Sierra de la Laguna)

• V. g. leucopolius:

• Great Basin of eastern Washington to south-eastern California and south-western Utah

• V. g. brewsteri:

• Sierra Madre Occidental of north-western Mexico (southern Sonora to Nayarit)

• V. g. connectens:

• Mountains of southern-central Mexico (Michoacán to Oaxaca)

One of these, victoriae has been claimed as a separate species, Cape Warbling Vireo. Another treatment is for this and three other subspecies (swainsonii, leucopolius, and sympatricus) to be split into Western Warbling vireo (would then be Vireo swainsonii), and the remaining subspecies to be Eastern Warbling Vireo (Vireo gilvus) with subspecies gilvus, brewsteri, eleanorae, bulli, amauronotus, and strenuus. The current consensus among worldwide checklist makers seems to be not to accept this split.
Subspecies swainsonii should be spelled swainsoni^[2].

[edit] Habitat

Treetops, especially large trees and along rivers and creeks

[edit] Behaviour

Individuals or pairs flit about in the treetops in wooded country, especially in riparian zones. Moves rapidly when foraging, but may perch in the same spot to sing for a several minutes. Often in the densest foliage, so hard to spot even when close.

[edit] Diet

Insects, caterpillars, insect eggs, and some fruits.

[edit] Vocalisation

Song: A warble, repeatedly frequently; 12-20 syllables for eastern birds, shorter for western birds.

[edit] References

1. Clements, JF. 2009. The Clements Checklist of Birds of the World. 6th ed., with updates to December 2009. Ithaca: Cornell Univ. Press. ISBN 978-0801445019.
2. 51st supplement to the AOU checklist of North American birds
3. Birds of North America online

• List of references

[edit] External Links