Varied Thrush Life History

Habitat

The Varied Thrush lives in dark, wet, mature forests in the Pacific Northwest. In its breeding range, which covers Alaska and tapers as it extends south to northern California, it inhabits forests dominated by coastal redwood, Sitka spruce, red alder forests, western hemlock, western red cedar, western larch, or Douglas-fir. In winter it may be found in a broader range of habitats, including parks, gardens, lakeshores, and riparian areas where fruit and berries are abundant. Back to top

Food

During breeding season, Varied Thrushes eat insects and other arthropods from the leaf litter; in winter they eat mostly berries and nuts. They forage by seizing dead leaves in their bill and hopping backward to clear a spot of ground before examining it for prey. In fall and winter, they switch to fruits and acorns, forming loose flocks around their food. Some of their typical fruits are snowberry, apple, honeysuckle, madrone, mistletoe, manzanita, toyon, ash, salal, cascara, dogwood, blueberry, huckleberry, salmonberry, and thimbleberry.Back to top

Nesting

Nest Placement

Females probably choose where to build the nest—usually in the understory of a mature forest, often in a spot surrounded by old nests (or even directly on top of one). They are usually around 10 feet off the ground and poorly concealed, close to the trunk of a small conifer.

Nest Description

The female gathers nest material and weaves an outer layer of fir, hemlock, spruce, or alder twigs. She adds a middle layer with rotten wood, moss, mud, or decomposing grass, which hardens into a dense cup about 4 inches across and 2 inches deep. Finally, she lines the cup with fine grasses, soft dead leaves, and fine moss, and drapes pieces of green moss over the rim and outside of the nest.

Nesting Facts

Behavior

Varied Thrushes forage on the ground, periodically moving to higher perches in the understory to sing or move between foraging sites. Males reach the breeding grounds before females and start singing to establish territories. They have several threat displays, beginning by cocking the tail, turning it toward an intruder, and lowering the wings. If the adversary remains, the displaying bird will face off, lowering its head, raising and fanning the tail, and spreading its wings out to its side. Occasionally, males peck at or lock bills with each other. While squabbling over territory or chasing away nest intruders, they may dive and swoop through dense vegetation, sometimes hitting branches along the way. Males may also defend small sites around bird feeders in the winter, though females seem to use alternative feeding sites to avoid competition. Varied Thrushes are thought to establish monogamous breeding pairs, but how long the birds stay together is not known. Back to top

Conservation

Varied Thrushes are fairly common, but populations declined by approximately 0.7% per year, resulting in a cumulative decline of about 32% between 1966 and 2019, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 35 million and rates them 12 out of 20 on the Continental Concern Score, indicating a species of relatively low conservation concern. However, Varied Thrush is included on the list of Common Birds in Steep Decline, for species that are still too numerous or widely distributed to warrant Watch-List status but have been experiencing troubling long-term declines. Because Varied Thrush live in mature and old-growth forests containing very large trees and tend to live in forest patches larger than about 40 acres, logging and forest fragmentation can cause habitat loss that reduces their numbers. Around human habitation, Varied Thrushes have proven very vulnerable to window strikes as well as predation by domestic and feral cats and collisions with cars. Varied Thrushes may benefit from reserves that have been established to protect the Northern Spotted Owl.

Credits

George, T. Luke. (2000). Varied Thrush (Ixoreus naevius), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Lutmerding, J. A. and A. S. Love. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.

Partners in Flight. (2020). Avian Conservation Assessment Database, version 2020.

Rosenberg, K. V., J. A. Kennedy, R. Dettmers, R. P. Ford, D. Reynolds, J. D. Alexander, C. J. Beardmore, P. J. Blancher, R. E. Bogart, G. S. Butcher, A. F. Camfield, A. Couturier, D. W. Demarest, W. E. Easton, J. J. Giocomo, R. H. Keller, A. E. Mini, A. O. Panjabi, D. N. Pashley, T. D. Rich, J. M. Ruth, H. Stabins, J. Stanton, and T. Will (2016). Partners in Flight Landbird Conservation Plan: 2016 Revision for Canada and Continental United States. Partners in Flight Science Committee.

Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2019). The North American Breeding Bird Survey, Results and Analysis 1966–2019. Version 2.07.2019. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

Wells, J. V., K. V. Rosenberg, D. L. Tessagalia and A. A. Dhondt. (1996a). Population cycles in the Varied Thrush (Ixoreus naevius). Canadian Journal of Zoology 74:2062-2069.

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