Varied Thrush

Males arrive on the breeding grounds before females and immediately begin establishing territories through song, singing most persistently at dawn, dusk, and after rain. The breeding habitat is dense, mature coniferous forest — the darker and wetter the better. Pairs are thought to be monogamous, though the duration of pair bonds between seasons is not well documented.

The female builds the nest alone, typically placing it around 1.5–4.5 m (5–15 ft) off the ground close to the trunk of a small conifer in the forest understory. Occasionally nests are placed much higher, and in the far north, nests may be very low in deciduous thickets or even on the ground. Females sometimes build directly on top of a previous nest, and old nests nearby appear to be a cue for site selection.

The nest itself is a bulky open cup constructed in three distinct layers. The outer layer is coarse fir, hemlock, spruce, or alder twigs. The middle layer is a dense matrix of rotten wood, moss, mud, or decomposing grass that hardens into a firm cup approximately 10 cm across and 5 cm deep. The inner lining is soft grasses, dead leaves, and fine moss, with pieces of green moss draped decoratively over the rim and outside of the cup.

Clutch size is 1–6 eggs, typically 3–4 along the coast and averaging 4 in interior populations. Eggs are pale sky blue, sometimes with sparse dark brown speckles, measuring approximately 2.8–3.5 cm long and 1.9–2.3 cm wide. Incubation is by the female alone and lasts approximately 12–14 days. Chicks hatch with eyes closed and bodies mostly bare, with sparse patches of grey down. Both parents feed the nestlings, which fledge after 13–15 days. Up to two broods may be raised per year when conditions allow.

The typical lifespan of a Varied Thrush in the wild is 3–5 years, with a maximum recorded longevity of 5.6 years. The oldest documented individual was a male banded in California in 1978 and recaptured at the same location in 1982 — at least 4 years and 9 months old at the time of recapture.

Adult apparent survival rates are strikingly low for a passerine of this size, estimated at around 0.43 (43% annual survival) from MAPS banding data collected between 1992 and 2006. This means that, on average, fewer than half of adult Varied Thrushes survive from one year to the next — a figure more typical of smaller, shorter-lived songbirds. The likely explanation is the species' irruptive and unpredictable winter movements: birds that wander far from their normal range in search of food face unfamiliar conditions, novel predators, and increased exposure to hazards such as window strikes and vehicle collisions.

For comparison, the closely related American Robin has a considerably longer maximum recorded longevity of around 13–14 years, though typical wild lifespans are also short. The Common Blackbird (Turdus merula), another Turdidae family member, has a maximum recorded longevity of over 21 years, though most wild individuals live only 2–3 years.

The Varied Thrush's low survival rate, combined with a clutch size of 3–4 eggs and up to two broods per year, suggests that productivity must be relatively high in good years to maintain population levels. The documented long-term decline of around 32% since 1966 therefore represents a genuine and concerning imbalance between productivity and survival.

The Varied Thrush is listed as Least Concern on the IUCN Red List (2016), with a global population estimated at approximately 35 million mature individuals by Partners in Flight (2020). However, the population trend is clearly downward. The North American Breeding Bird Survey recorded a cumulative decline of approximately 32% between 1966 and 2019 — roughly 0.7% per year. Some analyses cite steeper declines of around 2.5% per year, amounting to a 73% cumulative loss between 1966 and 2015.

The species is included on the Partners in Flight list of Common Birds in Steep Decline, with a Continental Concern Score of 12 out of 20.

The primary threat is the loss and fragmentation of mature and old-growth coniferous forest. Approximately 72% of original old-growth conifer forests in the Pacific Northwest have been lost since European settlement. The Varied Thrush's requirement for forest patches of at least 40 acres means that fragmented second-growth landscapes offer little suitable habitat. Logging remains the most direct driver of decline.

Climate change poses a significant long-term threat. Audubon Society climate models project that a 3°C temperature increase would eliminate 68% of the species' current habitat, shifting the range northward and compressing it considerably — placing it among the most climate-vulnerable forest birds in Audubon's analysis.

Additional mortality causes include window strikes, predation by domestic and feral cats, and vehicle collisions — hazards shared with most forest birds that venture into human-modified landscapes in winter. On a more positive note, the species may benefit indirectly from habitat reserves established to protect the Northern Spotted Owl, which occupies the same old-growth forest ecosystem. Population density shows regular 2-year cycles of abundance and decline linked to food availability, particularly oak mast production.

The Varied Thrush has one of the rarest colour variants documented in any North American passerine. In a small number of individuals, all the orange plumage is replaced by white — a condition resulting from leucism or albinism affecting the pigmentation of the orange feathers while leaving the dark slate-grey and black areas largely intact. Only five such white-orange individuals have been recorded since 1921, making this one of the least frequently documented colour variants in the entire family Turdidae.

The most famous of these white-orange birds was the first British record of the species: a leucistic individual found at Nanquidno, St Just, Cornwall, from 14 to 23 November 1982. The bird's extraordinary appearance — a thrush with white where orange should be, turning up on the far tip of southwest England — prompted considerable discussion among British ornithologists. Some speculated that the same genetic mutation responsible for the colour abnormality might also impair the bird's navigational abilities. This could potentially explain how it came to be on the wrong side of the Atlantic, though the hypothesis remains unproven.

Normal-plumaged Varied Thrushes are themselves occasionally subject to partial leucism, producing birds with white patches in the wing or tail. These are more frequently reported than the full white-orange variant but are still uncommon. The species' striking normal plumage — with its precise geometric pattern of slate, orange, and black — makes any deviation from the standard pattern immediately obvious, which may partly explain why colour variants in this species attract such disproportionate attention.

The Varied Thrush occupies a unique position in the family Turdidae as the sole member of the monotypic genus Ixoreus. The genus name was assigned by the French-American ornithologist Charles Lucien Bonaparte in 1854. Ixoreus derives from the Ancient Greek ixos, meaning mistletoe — a reference that arose from a taxonomic error. Bonaparte believed the Varied Thrush was related to mockingbirds because the naturalist William Swainson had illustrated both on the same plate of his book, leading Bonaparte to group them together. The mistake was eventually corrected, but the genus name — with its mistletoe etymology — was retained.

The species epithet naevius is Latin for "spotted" or "marked with spots", a reference to the bird's patterned plumage. The species was first formally described by Johann Friedrich Gmelin in 1789. Common regional names have included Canadian Thrush, Oregon Thrush, and Mountain Thrush — all reflecting the bird's geographic associations in different parts of its range.

Four subspecies are currently recognised. I. n. naevius (Gmelin, 1789) breeds along the coast from southeast Alaska to northern California. I. n. meruloides (Swainson, 1832) occupies interior Alaska and British Columbia south through the northern Rockies. I. n. carlottae (Brooks, 1929) is endemic to Haida Gwaii (Queen Charlotte Islands) in British Columbia. I. n. godfreii (Phillips, 1991) breeds in southern interior British Columbia, eastern Washington, and western Montana. The subspecies are distinguished primarily by differences in female plumage — male plumage is relatively consistent across the range.

In the Pacific Northwest, Varied Thrushes are occasional but welcome winter visitors to gardens, particularly during cold snaps or in years when natural food supplies are poor. They are most likely to appear between October and March, and their presence at a feeder is often announced by the sight of a boldly patterned bird standing motionless on the lawn before moving to the feeding area.

Ground-level feeding is essential — Varied Thrushes rarely use hanging feeders and are most comfortable foraging on a flat surface or low platform. Seed mixes containing millet and sunflower seeds are taken readily, as is suet placed on or near the ground. Fruit is particularly attractive: halved apples, raisins soaked in water, and berries placed on a ground tray will draw birds in. Planting berry-bearing shrubs such as snowberry, salal, manzanita, toyon, or native dogwood provides a natural food source that may encourage regular visits.

Varied Thrushes are shy birds and may take several days to become comfortable at a new feeding station. Minimising disturbance near the feeding area — keeping cats indoors and avoiding sudden movements near windows — significantly improves the chances of a bird settling in. Window strikes are a real hazard: applying window decals or external screens to large glass panes near feeders is strongly recommended, as collisions are one of the documented causes of mortality for this species.

In eastern North America, Varied Thrushes appear as rare winter wanderers, most often during irruption years when western food supplies fail. Birders who find one at their feeder should report the sighting to eBird — these records contribute to understanding the species' irruptive movements and long-term population trends.