Kirtland’s warbler  (Dendroica kirtlandii)

Kirtland’s warbler is classified as Near Threatened on the IUCN Red List 2006 (1) and is listed on Appendix I of the Convention on Migratory Species (CMS or Bonn Convention) (3).

This large warbler has a bright yellow breast and underside with black streaking on the sides. The male has a blue-grey back and the female is similar but paler, with a browner back. The black eye is encircled by a white ring that is broken to the left and right by black. The pointed beak is black, as are the legs. Juveniles are pale yellow and brown, but streaked with grey, with spots of grey on the throat. This species calls with a persistent ‘chip-chip-che-way-o’ (2).

Kirtland’s warbler breeds mainly in north and central Michigan, but singing males have also been recorded in Ontario and Quebec, Canada. They spend the winter in a small area of the Bahamas, as well as on the Turks and Caicos Islands (2).

The very specific habitat requirements of this species are the main cause of its threatened status. Despite nesting on the ground, Kirtland’s warbler will only nest amongst 9 – 13 year old jack pines (Pinus banksiana); taller stands are abandoned for a new site. Ninety percent of these birds nest in the drainage area of a single stream, as they require the well-drained soil type found there, known as Grayling sands. They winter in low scrub, moving to higher shrubs to roost at night (4).

Arriving first at the breeding site, the males return to their usual nest site and begin to sing immediately, defending their territory. Later, the females arrive to mate, selecting a male for the season based on his singing voice. The nest is constructed on the ground between young jack pines in late May, in time for egg-laying between late May and mid June. From three to six eggs are incubated by the female for 14 days, during which time the male brings food to his partner. After hatching, both parents tend to the chicks, each tending to only half the brood, which disperse just 9 or 10 days later (4).

Kirtland’s warbler feeds mainly on flying insects, although it also consumes pine needles, grasses and blueberries (4).

This species is heavily dependent on an extremely specialised and limited habitat which was originally maintained through regular, natural forest fires, providing a constant supply of young jack pines. However, white human settlers cleared much of this habitat and reduced the likelihood of forest fires. Initially, Kirtland’s warbler benefited from this action, but the brood-parasitic brown-headed cowbird (Molothrus ater) also thrived. The brown-headed cowbird lays an egg in the nest of Kirtland’s warbler, removing one of the warbler’s eggs, and tricking it into raising a cowbird as its own. Compounding this problem, the cowbird chick hatches before the warbler chicks and out-competes them for food. As a consequence, the breeding success of Kirtland’s warbler has declined dangerously (4).

To combat the two main threats to this species, habitat loss and brood-parasitism, the nature authorities of Michigan began a cowbird trapping programme in 1972 which was extremely successful, reducing brood-parasitism from 70% to 3%. Habitat management has also been undertaken, resulting in a threefold increase in suitable Kirtland’s warbler habitat. The number of Kirtland’s warblers is clearly directly linked to available habitat as, following management work, the population quadrupled between 1990 and 2000. Collaborative efforts between the United States and the Bahamas have improved the quality of wintering grounds and led to ongoing surveying. More economical cowbird control is now being investigated. The success of conservation efforts for Kirtland’s warbler is well documented and referred to in the conservation community (2).

View information on this species at the UNEP World Conservation Monitoring Centre.

For further information on this species see:

State of Michigan – Department of National Resources:
http://www.michigan.gov/dnr/0,1607,7-153-10370_12145_12202-32591--,00.html

For more information on this and other bird species please see:

• BirdLife International:
  http://www.birdlife.org