Varied Thrush    Ixoreus naevius

Migratory Status: Short-distance migrant

PIF Population Estimate: 26 000 000

Percent of western hemisphere population breeding in boreal forest: <25%

BAM Effective Detection Radius (m) : 135.67

PIF Maximum Detection Distance (m) : 125

Canadian BBS Population trend: -0.3 n.s. (-1.3 to 0.8)

Life History

The Varied Thrush is a large and conspicuous bird of north-western North America. The distinctive and highly recognizable combination of slate-grey and orange plumage has made it an emblematic species for numerous conservation organizations and initiatives. Its haunting song, consisting of long, whistled notes on a single pitch, is an easily recognizable symbol of the region’s forests.

The breeding range includes most of the forested areas of Alaska, south through British Columbia, northeast Oregon, and central Idaho to northern California. It also extends east to the foothills of the Rocky Mountains, including southwest Alberta and northwest Montana. Non-migratory populations and some over-wintering individuals occupy portions of coastal Alaska and British Columbia in the non-breeding season. Most populations over-winter from northern Washington and Idaho, south to central and southern California. Some birds winter as far south as northern Baja California. The species is also a well-known vagrant during the non-breeding season, recorded in almost every Canadian province and nearly all of the Unites States.

The diet during the breeding season typically consists of arthropods, such as ground dwelling insects; when available, fruit is an important part of the diet. On the wintering grounds, the Varied Thrush consumes a higher proportion of seeds, nuts, and acorns. Foraging typically occurs on the ground, where leaf litter is tossed aside with the bill, and cleared areas are searched for prey. Berries, fruits, and seeds are consumed while birds are perched in shrubs or trees, or are taken directly off the ground.

Based on numerous continental-scale monitoring programs, the Varied Thrush appears to undergo population spikes every two to five years. The masting of oak trees in eastern North America may be a strong driver of the cyclical patterns in population abundance and widespread movements of this species, but overall, the mechanism(s) responsible for this variation are not well understood.

Reference(s)

George, T. L. 2000. Varied Thrush (Ixoreus naevius), The Birds of North America Online, . A. Poole, Ed. Ithaca: Cornell Laboratory of Ornithology; Retrieved from The Birds of North America Online database: http://bna.birds.cornell.edu/bna/species/541