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Dendroica kirtlandiiKirtland's warbler

By Ethan Kane

Geographic Range

The Kirland's Warbler breeds in northern central Michigan, in an area that is about 100 miles long and 60 miles wide. It is also a neotropical migrant, spending the winter in the Bahamas.

Habitat

The Kirtland's warbler nests in groves of young Jack pines (Pinus banksiana) ranging in height from 5 to 18 feet. They also seek out areas with ground cover composed of blueberries, bearberry, or sweetfern. These warblers also require a very specific soil type, the Grayling Sands, which is important because they nest on the ground and their nests would be flooded if rain water did not drain away quickly. For this reason, nearly 90% of these birds breed in the drainage area of a single stream.

Their winter habitat in the the Bahamas consists of low scrub. During the night they retreat to higher shrubs to roost.

Physical Description

  • Average mass
    15.5 g
    0.55 oz
    AnAge

Reproduction

Nests are constructed in late May, followed by the laying of eggs in late May to mid-June. The number of eggs per clutch ranges from 3 to 6. In the rare event that a pair has a second clutch, fewer eggs will be laid than in the first. The female incubates the eggs for approximately 14 days before hatching occurs. During the incubation period, defense and care of the nest are predominantly the responsibilty of the female; however, the male will bring food to her. After the eggs hatch, both parents tend to the needs of the altricial young. The young gain weight rapidly during the first five days after hatching, doubling their weight every two days. During the last three days in the nest, their growth rate decreases and their energy is directed towards providing their own body warmth, plumage development,and heightened physical activity. The young leave the nest 9-10 days after hatching. During the fledging period, the brood is divided in half, each parent taking care of select offspring. The post juvenile molt occurs approximately one month after fledging.

  • Average eggs per season
    5
    AnAge
  • Average time to hatching
    14 days
    AnAge
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    365 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    365 days
    AnAge

Lifespan/Longevity

Behavior

Males are the first to arrive at the nesting grounds in the spring, and they begin singing immediately. Females soon follow with late arriving males. Each male usually returns to the territory that he occupied the previous year; however, this true of females. Males aggressively defend their territories against other males, but territories are usually in close proximity to those of neighboring males, indicating a tendency towards loose colonialism.

Communication and Perception

Food Habits

This species feeds primarily on insects; however, it is known to sample an array of other food materials including pine needles, grasses, and bluberries. Food is gathered by gleaning and flycatching on the wing.

Economic Importance for Humans: Positive

Negligible

Economic Importance for Humans: Negative

The warbler's endangered species status has affected the ability of private landowners to develop property containing warbler habitat.

Conservation Status

The Kirtland's Warbler has been the focus of much attention over the last 25 years because of its rarity and need for a very specific habitat. Natural forest fires were the original providers of such habitat, but the advance of white settlers resulted in the clearing of much of Michigan's natural forests. At first, the warbler benefited from such clearing; however, so did the Brown-Headed Cowbird (Molothrus ater). The Cowbird had a major impact on the warbler as a nest parasite. Cowbirds lay their eggs in the nests of other birds and leave the rearing of their young to these hosts. Cowbird young usually develop much faster than the young of the host species and are thus able to out-compete the hosts' young for food resources. Many of the hosts' young die as a result. Recognition of the effects of this phenomena on the Kirtland's Warbler in the early 1970's lead to a program of killing Cowbirds in the warbler's range. This program, coupled with the management of breeding grounds by way of controlled burns, has significantly aided the warbler. However, the Kirtland's Warbler seems to be faced with other problems that effect it during migration or during its time in the Bahamas. As a result, the breeding population in Michigan has not changed significantly recently from spring to spring.

Contributors

Ethan Kane (author), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

References

Harrison, Hal H. 1984. Wood Warbler's World. Simon and Schuster, New York. pp. 172-178.

Mayfield, Harold. 1960. The Kirland's warbler. Cranbrook Institute of Science, Bloomfield Hills, MI. pp. 18, 19, 44, 45, 53, 54, 80, 84, 87, 89, 91, 100, 106, 107, 110, 123, 124.

Peterson, Roger Tory. 1980. A Field Guide to the Birds East of the Rockies. Houghton Mifflin, Boston. pp. 234-235.

Schreiber, Rudolf L., Anthony W. Diamond, Roger Tory Peterson, and Walter Cronkite. 1989.

Save the Birds. Houghton Mifflin, Boston. pp. 190- 191.

Mayfield, H. F. 1992. Kirtland's Warbler (Dendroica kirtlandi). Birds of North America, 19:1-16.

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