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Bird Habitat Conservation Toolkit

Image of Bird
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)
Overview
status
AlbertaSecure
British ColumbiaBlue
Primary Habitat
Aspen/Mixedwood with shrubs
Nest Type
Ground
Territory Size
0.25–0.48 ha
Nest Reuse
No
Breeding Window
Jan
Feb
Mar
Apr
May
Jun
Jul
Jul
Aug
Sep
Sep
Oct
Nov
Dec
Peak: Mid-July to late August
Stand-Level
Patches >5 ha containing mature aspen (>40 years) and fruiting species in the shrub layer.
Landscape-Level
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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