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Bird Habitat Conservation Toolkit

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The Connecticut Warbler is less well-studied than other warblers due to its inconspicuous behavior. Alberta, Saskatchewan and BC represent the western edge of its breeding range.

Connecticut Warbler

(Oporornis agilis)
British ColumbiaBlue
Primary Habitat
Aspen/Mixedwood with shrubs
Nest Type
Territory Size
0.25–0.48 ha
Nest Reuse
Breeding Window
Peak: Mid-July to late August
Patches >5 ha containing mature aspen (>40 years) and fruiting species in the shrub layer.
Patches within 5 km of larger mature aspen or mixedwood forests.

Habitat Ecology

  • Connecticut Warblers are mainly found in deciduous forests and aspen-leading mixedwoods with a well-developed shrub layer (aspen, rose, beaked hazelnut, alder, willow, and fruiting shrubs).1,2 However, its habitat selection is highly variable across its range:
  • It is also found at the edges of small meadows, wetter stands with high tamarack cover and low shrubs,1,2 and in eastern North America, muskegs and lowland conifer forests.3
  • This species occupies a range of stand ages ranging from 0–10 years to mature and old (>76 years) aspen and mixedwood forests.4,5
  • Its nest is built on or near the ground, often in thickets, clumps of vegetation, or at the base of a shrub.1

Response to Forest Management

  • This species is more abundant in recently burned than recently harvested forest,6 and is more abundant in burned riparian forest than intact or partially-harvested riparian buffers.7
  • In BC, the largest threats to Connecticut warbler include 1) herbicide application to reduce understory vegetation and deciduous regeneration and 2) logging of aspen stands.1
  • Connecticut Warbler has shown mixed responses to retention harvesting. High retention (>20%) appears to have a negative effect, however lower retention levels (e.g., 10%) may benefit this species.8
  • Regenerating clear-cut stands (i.e., no planned retention) are likely to contain Connecticut Warblers from 15–25 years postharvest.9

Stand-level Recommendations

  • Managers should establish large retention patches (>5 ha) where possible, containing mature aspen or poplar and a well-developed shrub and herbaceous layer (particularly fruiting shrubs).5,10
  • Retention harvesting (e.g., 10% retention in small, evenly distributed clumps) may be beneficial.8 Avoiding shrub and understory suppression using herbicides is also important for this species.1
  • Mid-seral regenerating stands (15–25 years postharvest) may provide habitat for this species.9

Landscape-level Recommendations

  • Forest management within the natural range of variation, including clearcuts, blocks containing low overall retention, blocks containing large (>5 ha) retention patches, burned forest, and larger areas of unharvested deciduous forest, is expected to benefit Connecticut Warblers on the landscape.
  • Smaller patches and remnants have been shown to have greater benefits to this species when >5 ha and/or located closer to unharvested forest. Patches, remnants, and set-asides (preferably consistent with NRV patch sizes) are recommended with the following additional parameters:
  • Pure aspen or mixedwood forest set-asides should contain old aspen (>40 years) and developed herbaceous and shrub layers.11
  • Stands/remnants should be either very large OR smaller and located within 5 km of larger areas of high forest cover.5
  • Stands/remnants located on flat sites or gentle south- or west-facing slopes may have additional habitat value.11

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