Black-throated Green Warbler (Dendroica virens)

Description
Black-throated Green Warbler

Size

  • The black-throated green warbler is a small warbler measuring about 11 to 12 centimetres (four to five inches) long.

Appearance

  • Distinguishing characteristics for the male include:
    • Bright yellow face
    • Black throat and upper breast
    • Olive green crown, back and wings
    • Black tail
    • Contrasting white abdomen
  • The female is duller in appearance, and her throat and breast are mottled with black and yellowish-white, rather than solid black.

Voice/Call

  • The black-throated green warbler’s song is a distinctive buzzy zeee-zee-zee-zoo-zeee.
Distribution
  • Is a migrant wood warbler that inhabits the boreal forest and foothills of Alberta.
  • Breeds across the boreal forest of Canada and the northeastern United States, and winters in Mexico and Central America.
  • Is found in northern and western Alberta, where it approaches the northern limits of its range.
Natural History

Habitat

  • The black-throated green warbler occurs in older mixedwood forests (80 to 130 years) of trembling aspen, balsam poplar and white spruce.
  • It avoids disturbed and edge habitats as well as small forest patches.

Food

  • The black-throated green warbler is almost entirely insectivorous.
  • Breeding birds tend to take a high volume of butterfly and moth larvae, but will forage opportunistically on other abundant prey (e.g., midges along a lakeshore).
  • This warbler is also known to consume:
    • Adult moths
    • Ants
    • Beetles
    • Flies
    • Gnats
    • Mites
    • Spiders
    • True bugs
    • Wasps
  • During migration, it will also eat berries and other vegetative material.

When Active

  • Black-throated Green Warblers arrive in Alberta from mid- to late-May and likely leave the province before the third week of September.
Reproduction and Growth

Breeding Behaviour

  • Males arrive several days earlier than females, and immediately begin establishing territories by singing and exhibiting aggression towards other males.
  • Very few black-throated green warbler nests have been documented, but studies suggest that most nests are built in small or large coniferous trees, fairly close to the trunk.
  • Clutches, which are likely initiated in mid-June, contain three to five eggs.
  • The incubation period is roughly 12 days and hatching is synchronous.
  • Incubation and nestling care is almost entirely done by the female.

Growth Process

  • Fledging occurs after 8 to 11 days and successful nests probably fledge two to four young.
  • Young can fly strongly within a few days of fledging at which point the adults may separate, each taking part of the brood.
  • Young may remain with the parents for up to one month.
Conservation and Management

Status

The black-throated green warbler are classified as Sensitive in the current General Status of Alberta Wild Species report. See:

Also see the Status of the Black-throated Green Warbler in Alberta report at:

In a subsequent detailed status assessment, Alberta’s Endangered Species Conservation Committee identified the black-throated green warbler as a Species of Special Concern—a species that without human intervention may soon become threatened with extinction. See information on the Endangered Species Conservation Committee and Species of Special Concern at:

Issues

  • Timber harvesting has increased significantly in Alberta in recent years, and regenerating forests will not reach a sufficient age to support black-throated green warblers before being harvested again.
  • Loss of wintering habitat in Central America may also be affecting black-throated green warbler populations.

Current management

Under Alberta’s Wildlife Act, the black-throated green warbler is designated as a non-game animal and it is ille.gal to kill or harass individuals or disturb their nests at any time of the year.

Alberta’s Endangered Species Conservation Committee has recommended the conservation of its habitat through long-term forest management focused on maintaining populations that are well distributed over the species’ historical range.

Modifications to resource extraction activities that currently affect the preferred habitat of the black-throated green warbler will be critical to lessen their impact on this species

A Species of Special Concern management plan is being developed for this species; see information on identification and management of species of special concern at:

 

Page Information

Updated: Jan 8, 2014