- The Varied Thrush is generally considered a species of mature and old coniferous forests.1 They are associated with old, unharvested cedar/hemlock and spruce/fir forests,2 lodgepole pine/white spruce,3 Douglas fir/western hemlock/western red alder,4 and black spruce/tamarack.
- They are associated with wet, upland, old forests5 and positively associated with herbs, ferns, and berry-producing shrubs in the understory.6
- The Varied Thrush is often described as a species of dark, wet, and mossy forests.1
- Nests are usually built in the understory vegetation of mature forests (and sometimes second-growth). They may be built on the lower branches of a small conifer, on the ground, in shrubs, or more.1
- While Varied Thrushes do not reuse nests, they tend to build nests near or even on top of old nests.1
Response to Forest Management
- This old forest-associated species is rarely observed in young harvested stands, including retention harvests. It was absent from clearcuts and retention harvests7 and declined in thinned stands.8–10
- Two studies of riparian buffers in the Pacific Northwest found conflicting results. Riparian buffers >30 m supported Varied Thrushes, however it is unclear whether these buffers will support numbers comparable to unharvested forest.11,12
- Low-intensity harvests (e.g., single-tree up to 10 ha openings totaling 30% volume removal within 30 ha blocks) mitigated harvesting effects, particularly in harvests <10 ha.13
- The Varied Thrush showed higher resilience to harvesting in the ESSF dry cool biogeoclimatic zone, where it was common in second-growth stands >7 years (compared with the MS dry cool biogeoclimatic zone, where it was common in second-growth stands >27 years).14
- Very small harvesting entries (<10 ha) may reduce negative short-term effects on the Varied Thrush,13 and understory protection may improve habitat value after >7 years,14 in Engelmann spruce-subalpine fir forests.
- Riparian buffers >30–35 m are recommended in old conifer habitats, however these may only provide marginal benefits.11,12
- Large conifers with low foliage density near the top, near water or drainages and on steep slopes, may represent potential song posts and thus be useful as retention patch anchor points. However, this recommendation is derived from research conducted in coastal redwood forests and local studies are suggested.15
- The Varied Thrush’s high sensitivity to harvest and thinning, particularly in lodgepole pine and Douglas fir forests, suggests this species will have its highest densities in older-than-rotation, wet, upland coniferous forests represented on the landscape.
- Old unfragmented forest patches >16 ha, or larger sizes consistent with NRV approaches, are considered to be of the highest value to this species. However, this threshold was determined for coastal redwood forests and may not apply to forests in interior BC or Alberta.16