Black-throated Green Warbler
- Black-throated Green Warblers are found in a wide range of forests containinglarge white spruce (including mixedwoods and deciduous-leading forests), with their highest densities in 100–130 year stands where they often use small-scale canopy gaps.1,2 They are also known to occupy young to mature forests.3,4
- In BC, mature riparian white spruce or mixedwood forests are considered their most important habitat, while mature or old deciduous forests containing mature spruce may attract them.3
- These warblers forage and nest on large-diameter (>50 cm dbh) white spruce.1
- Black-throated Green Warblers usually nest in conifers5 but have shown some preference for paper birch with ~20 cm dbh in Alberta.1
Response to Forest Management
- This species is most abundant on unlogged landscapes6 with a strong preference for forests exceeding the rotation age.7
- In deciduous-dominated forests in Alberta, they disappeared from stands with 2–6% retention but were present at low levels in harvests with 40% retention.⁸ They were unlikely to be present in clearcut (i.e. no planned retention) stands up to 33 years postharvest.9
- They may be sensitive to fragmentation: in New England, they were absent from forests <100 ha,5 and there is evidence that they avoid cutblock edges and crossing openings ≥25–40 m wide.2,10
- High retention (>40%) may be needed to reduce short-term harvest effects on this species, however these recommendations are based on studies from aspen-leading boreal mixedwood forests and may not be applicable to spruce-leading or -dominated forests.11,12
- Retention patches placed ≤40 m apart may make it easier for these warblers to travel across large harvest areas, however this strategy has not been tested for efficacy.
- Mixed-species retention patches (0.5 ha) containing large-diameter spruce may provide suitable nesting habitat in 30–60 years within a harvest block.2
- Riparian buffers >20 m may support pairs, but larger (>60 m) buffers will likely be more effective.13
- Mixedwood management to maintain coniferous-deciduous mixed stands on the landscape, as is present under NRV scenarios, will benefit this species.
- Old (100–130 year-old) mixed and spruce-leading stands >100 ha will provide important habitat on intensively-managed landscapes, as retention patches are expected to take several decades to provide suitable breeding habitat.2
- The role of older-than-rotation stands will likely be most important in BC, where its range is extremely limited and riparian spruce or mixed forests are highly valuable.3