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Connecticut warbler

Oporornis agilis

What do they look like?

In general, Connecticut warblers can be identified by their grey or brownish hood, which extends to their throat, along with their olive upperparts and yellow or yellowish-white underparts. These birds also have white eye-rings year round. Males and females look similar, although their plumage changes slightly throughout the year. In the spring, adult males tend to have olive-green and brownish upperparts and blackish wings and tails that lack any white markings. Their crown plumage is slate gray and they have a complete white eye-ring. The sides of their head, throat, and upper breast are also slate gray, but paler on their throat. The rest of their underparts are yellow and olive-green. In the fall, adult males are similar to adults in the spring; however, the crown is browner. Juvenile males look similar to adult males except their crown is olive-brown with a yellowish-brown color on their throat. Eye-rings are also buffy. Juveniles also have a paler bill and legs compared to adults. In the spring, adult females look similar to adult males except their crown is brownish and olive-green. Their cheeks, throat, and upper-breast are brownish. In the fall, adult females look similar to adult males in the spring, except their upperparts and breasts are browner. It is very difficult to tell juvenile females apart from adult males in the fall. Connecticut warblers weigh an average of 15 g and are 13 to 15 cm long. Their average wingspan is 23 cm. This species is often confused with mourning and Macgillivray's warblers as they look similar and are found in similar areas. Mourning warblers do not have eye-rings and have black patches on their breast and Macgillivray's warblers have broken eye-rings and a dark colored chest. These species can be told apart as Connecticut warblers are larger, have complete white eye-rings, and do not have any black color on their breast. (Chapman, 1907; Curson, et al., 1994; Pitocchelli, et al., 1997)

  • Sexual Dimorphism
  • male more colorful
  • Average mass
    15 g
    0.53 oz
  • Range length
    13 to 15 cm
    5.12 to 5.91 in
  • Average wingspan
    23 cm
    9.06 in

Where do they live?

Although Connecticut warblers (Oporornis agilis) are rare and difficult to study, their general range includes Southern Canada, the north-central United States south to central South America, and parts of the eastern United States. Their summer range has been difficult to record, whereas their winter range includes Venezuela, Brazil, and other parts of northern South America. This species travels different routes during their two yearly migration periods, which is somewhat rare for a migratory bird. Their spring migration takes them through Florida to the Mississippi Valley, while their fall migration involves flying eastward to New England and south to the West Indies and South America. (Chapman, 1907; Curson, et al., 1994; Harrison, 1984)

What kind of habitat do they need?

Connecticut warblers live in grassy areas in forests as well as low, damp woods or swampy wilderness. These birds can also be found in fields that are brushy or weedy. Members of this species may choose different habitats depending on where they live. In addition, Connecticut warblers are commonly found in spruce-tamarack forests that are poorly drained as well as drier oak-pine forests and Jack pine forests. Their breeding grounds are usually dry, open poplar woods, black spruce tamaracks, or muskeg bogs such as those of the north-central United States and southern Canada. (Bent, 1963; Harrison, 1984; Pitocchelli, et al., 1997)

  • These animals are found in the following types of habitat
  • terrestrial

How do they reproduce?

Although the type of mating system used by Connecticut warblers is not known, most related birds are either polygynous, where one male mates with several females, or promiscuous, where both males and females have multiple mates. (Pitocchelli, et al., 1997; Verner and Willson, 1966)

Connecticut warblers breed in eastern British Columbia and central Alberta in the north, east to northeastern Ontario, and south to northern Michigan. Breeding takes place in the summer, usually from mid-June to early August. Clutch sizes vary from 3 to 5 eggs, with an average of 4 eggs. These warblers create nests on the ground that are deep, compact, rounded cups made of fine dry grasses, leaves, and moss-like fibers lining the bottom. Females incubate eggs using the featherless area on their underside, known as an incubation patch, although the amount of time the eggs are incubated before hatching is unknown. (Bent, 1963; Curson, et al., 1994; Pitocchelli, et al., 1997)

  • How often does reproduction occur?
    Connecticut warblers produce one clutch per season.
  • Breeding season
    Their breeding season is in the summer, from June to August.
  • Range eggs per season
    3 to 5

Females brood the eggs. Once the eggs hatch, parental care involves both parents. They help feed their young at their nest, this usually continues until the young fledge. The fledglings are helpless the first week after hatching and are dependent on their parents. Families stay together for about two weeks after fledging, when the young become slightly more independent. (Curson, et al., 1994; Pitocchelli, et al., 1997)

  • Parental Investment
  • female parental care
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female

How long do they live?

The lifespan of Connecticut warblers has not been established. However, in New Jersey, a banded Connecticut warbler was estimated to be about 4 years old. The estimated lifespan for similar species is 7 years for mourning warblers, 6 years for Kentucky warblers, and 4 years for MacGillivray's warblers. Aside from being preyed upon, these birds may have a shortened lifespan as a result of crashing into human-made objects such as buildings. (Pitocchelli, et al., 2012; Pitocchelli, et al., 1997)

How do they behave?

Connecticut warblers have been described as a shy species. These birds are often found walking quietly in their habitat but they are also known to hide in their surroundings. When they move, their tail moves up and down as though it is bouncing. Although this species is often territorial and solitary, they may form flocks of up to 25 birds when they migrate. Likewise, these birds are known to feed alongside other bird species when they are in their breeding areas. Adult males are territorial. They are the most territorial during the summer, especially during breeding season. This species is solitary in the wintertime. (Bent, 1963; Curson, et al., 1994; Pitocchelli, et al., 2012; Pitocchelli, et al., 1997)

Home Range

The exact home range size for this species is not known. These birds maintain territories during the breeding season, although the territory sizes can vary based on their habitat. In Minnesota, breeding territories as small as 0.24 ha were seen in open habitats, whereas territories as large as 0.48 ha were seen in more closed habitats. (Pitocchelli, et al., 2012)

How do they communicate with each other?

Connecticut warblers mostly communicate through calls and songs. These birds make sharp, high-pitched calls while they fly. Alarm calls sound metallic such as "plink" or soft like "ploit" and are made when predators are near their nests or fledglings. Male and female adults may share call notes. Their songs can be repetitive two-part or three-part phrases. They are loud and can be heard from far distances. Their song pattern is similar to that of common yellowthroats and their pitch and rhythm are similar to that of Kentucky warblers. Their songs are normally heard on the breeding grounds, especially during the spring migration period. This species is much quieter during the fall. (Curson, et al., 1994; Pitocchelli, et al., 1997)

What do they eat?

Connecticut warblers feed on insects such as beetles, as well as spiders, snails, berries, and even small seeds. In general, warblers also feed on butterfly larvae and caterpillars. (Bent, 1963; Curson, et al., 1994)

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods
  • mollusks
  • Plant Foods
  • leaves
  • seeds, grains, and nuts
  • fruit

What eats them and how do they avoid being eaten?

Adult Connecticut warblers distract predators from their nests by pretending to be injured. These birds also stretch their wings out from their body in order to look bigger and frighten predators away. These warblers are very cautious of intruders and predators and retreat into dense shrubbery if they see one. These birds may respond to intruders near their nest by making scolding calls, which can last up to 30 minutes. The specific species that prey on Connecticut warblers have not been identified. (Bent, 1963; Curson, et al., 1994; Pitocchelli, et al., 1997)

What roles do they have in the ecosystem?

Connecticut warblers are victims of brood parasitism by brown-headed cowbirds. When this occurs, a brown-headed cowbird lays its eggs in the Connecticut warbler nest. As a result, Connecticut warblers care for brown-headed cowbird young, which may out-compete their own young. (Pitocchelli, et al., 1997)

Commensal or parasitic species (or larger taxonomic groups) that use this species as a host

Do they cause problems?

There are no known negative effects of Connecticut warblers on humans.

How do they interact with us?

Connecticut warblers are not known to provide any benefits to humans.

Are they endangered?

Although their populations are declining, Connecticut warblers are considered a species of least concern. The population size is large enough and is not declining fast enough to be considered a vulnerable species. Populations may be declining due to over-collecting, as well as habitat loss including fragmentation of the forests where they live. Conservation methods have not been established for this species due to their conservation status. (Pitocchelli, et al., 1997)


Meher Ahmed (author), The College of New Jersey, Matthew Wund (editor), The College of New Jersey, Leila Siciliano Martina (editor), Animal Diversity Web Staff.


Bent, A. 1963. Life Histories of North American Wood Warblers. New York: Dover Publications, Inc.

Chapman, F. 1907. The Warblers of North America. New York: D. Appleton and Company.

Cooper, J., S. Beauchesne. 2004. "Connecticut Warbler" (On-line pdf). Accessed March 06, 2014 at

Curson, J., D. Quinn, D. Beadle. 1994. Warblers of the Americas. New York: Houghton Mifflin Company.

Harrison, H. 1984. Wood Warblers' World. New York: Simon and Schuster.

Pitocchelli, J., J. Bouchie, D. Jones. 1997. Connecticut Warbler. The Birds of North America, 320: 1-16.

Pitocchelli, J., J. Jones, D. Jones, J. Bouchie. 2012. "The Birds of North America Online" (On-line). Connecticut Warbler (Oporornis agilis). Accessed July 25, 2014 at

Verner, J., M. Willson. 1966. The Influence of Habitats on Mating Systems of North American Passerine Birds. Ecological, 47/1: 143-147. Accessed May 05, 2014 at

University of Michigan Museum of ZoologyNational Science Foundation

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Ahmed, M. 2014. "Oporornis agilis" (On-line), Animal Diversity Web. Accessed February 23, 2024 at

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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