Bird of the Month - Varied Thrush

By Andy McCormick

Varied Thrush

Ixoreus naevius
Length 9.5”
Wingspan 16”
Weight 02.7 oz (78 g)
AOU Alpha Code VATH

“Classically a bird of mature, dense, unfragmented, moist coniferous forest,” the Varied Thrush is a Pacific Northwest specialty (Dunne).

Although seen most often in winter, the Varied Thrush is a breeding bird of the Olympics and Cascades and may also be found in the Blue Mountains of southeast Washington. It prefers the dark, shady retreats in the dense stands of Douglas fir, western hemlock, and western red cedar. Arthur Cleveland Bent reports that the first time he saw a Varied Thrush was in Kirkland, WA and he quotes W. Leon Dawson who said, “The Varied Thrush loves rain as a fish loves water; while as for the eternal drizzle, it is his native element and vital air,” (Bent).

The Varied is our most colorfully plumaged thrush. The blue gray head, back, and rump is set off by the burnt orange throat, belly, and wing pattern including two striking wing bars. It also sports an orange eyebrow stripe. The black chest stripe is reminiscent of the Northern Flicker.

ETHERIAL SONG

The song of the Varied Thrush is an eerie, slow, extended single note repeated about every ten seconds on a different pitch. It seems ideal for the misty, dark forests this thrush inhabits. It seems to come from nowhere and it can carry for a long distance in the forest. Research on song structure suggests that the pitch is changed to prevent habituation by neighbors (George). You can hear the song of the Varied Thrush at the Macaulay Library

The singing of the Varied Thrush increases after arrival on breeding territory in late April and early May. These thrushes are difficult to study because they breed in such dark and secluded places. We know that they build a nest in a conifer within a few meters of the ground. Usually three to four light blue eggs are deposited and incubated by the female for about two weeks. Both parents feed the nestlings, but it is not known how much time passes before fledging (Kaufman).

STATUS AND DISTRIBUTION

The Varied Thrush is a short distance migrant. However, those that nest farthest north leap-frog shorter-distance migrants and move the farthest south to southern California forests. Many Varied Thrushes are year-round residents in Washington and make an altitudinal migration to lowlands in winter. The population expands in winter as these resident birds are joined by wintering migrants from the north. Every two to five years these thrushes can have irruptive years when larger numbers move south (George). They are ground feeders and will leave areas of deep snow to find forested areas where the ground may be protected from snowfall.

It is the lone member of the genus Ixoreus, from the Greek ixos for mistletoe or mistletoe berry. I could not find a good reference for how this bird was given its scientific name except a note that it has been seen feeding on mistletoe berries. However, the Varied Thrush feeds mostly on insects it finds while foraging on the ground, and supplements insects during breeding season with huckleberries, thimbleberries, salmonberries and acorn mast. Mistletoe berries must make up a very small portion of their diet. The species epithet, naevius refers to the Latin naeuus, a discolored mark on the skin or birthmark, implying varied. The English name reflects the varied markings of the plumage (Holloway).

CONSERVATION

There are no conservation programs in place for the Varied Thrush since it is considered abundant. However, because breeding abundance of the Varied Thrush is greater in mature old-growth forests and reduced along forest edge, they are susceptible to forest fragmentation and apparently are not found in smaller forested areas. Maintaining old growth forests is probably the best way to insure healthy populations of Varied Thrush into the future.

References available upon request from amccormick@eastsideaudubon.org.