Oporornis agilisConnecticut warbler

Geographic Range

Although Connecticut warblers (Oporornis agilis) are rare and difficult to study, their general geographic 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 the winter range for these warblers includes Venezuela, Brazil, and other regions in northern South America. This species travels different routes during their two yearly migration periods, which is relatively rare among migratory birds. Their spring migration takes them through Florida to the Mississippi Valley, while their fall migration pattern includes flying eastward to New England and south to the West Indies and South America. (Chapman, 1907; Curson, et al., 1994; Harrison, 1984)


Connecticut warblers inhabit grassy areas in spruce or deciduous forests as well as low, damp woods or swampy wilderness. Fields that are brushy, weedy, or fallow are also favored. Habitat choice can differ across the breeding range. Additionally, spruce-tamarack forests that are poorly drained as well as drier oak-pine forests and Jack pine forests are common areas occupied by this species. 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)

Physical Description

Generally, these warblers can be identified from their grey or brownish hood, which extends to the throat, along with olive upperparts and yellow or yellowish-white underparts. White eye-rings are present in all plumages. Males and females are similar in overall appearance but do have slight seasonal variations. In the spring, adult males tend to have olive-green and brownish upperparts and blackish wings and tails that lack any white markings. The crown plumage is slate gray and there is a complete white eye-ring. The sides of the head, throat, and upper breast are also slate gray, but paler on the throat. The rest of the 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 are similar to adult males except the crown is olive-brown with a yellowish-brown color on the throat, relative to the gray in adults. Eye-rings are also buffy. Other juvenile characteristics include having a paler bill and legs relative to adults. In the spring, adult females have a similar appearance to adult males except the crown is brownish and olive-green. The cheeks, throat, and upper-breast are brownish. In the fall, adult females are similar in appearance to adult males in the spring, except the upperparts and breast are browner. Juvenile females are reportedly indistinguishable from adult males in the fall. Connecticut warblers weigh an average of 15 g and are 13 to 15 cm long. The average wingspan is 23 cm. This species is often confused with mourning and Macgillivray's warblers as they are morphologically and ecologically similar. Mourning warblers lack eye-rings and feature black patches on the breast and Macgillivray's warblers have broken eye-rings and a dark colored chest. These species can be distinguishing by the larger size, complete white eye-ring, and lack of black color on the breast of Connecticut warblers. (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


The mating system of Connecticut warblers has not been identified; however, birds in order Passeriformes are generally polygynous or promiscuous. (Pitocchelli, et al., 1997; Verner and Willson, 1966)

The breeding range of Connecticut warblers includes eastern British Columbia and central Alberta in the north, east to northeastern Ontario, and south to northern Michigan. Breeding takes place in the summer season, 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 in only a single incubation patch. The duration of incubation has not been recorded. (Bent, 1963; Curson, et al., 1994; Pitocchelli, et al., 1997)

  • Breeding interval
    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

In terms of parental investment, brooding is done by the female. Parental care involves both parents and once the eggs hatch; they help feed their young at their nest, usually until they fledge. The fledglings are helpless the first week after hatching and are dependent on their parents. Families remain 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


The lifespan of Connecticut warblers has not been established. However, in New Jersey, a banded individual had an estimated age of about 4 years. Similar species, such as mourning warblers and Kentucky warblers have an estimated lifespan of 7 and 6 years, respectively. While another related species, MacGillivray's warblers have an estimated lifespan of about 4 years. Aside from predation, these birds may experience mortality due to in-air collisions with human-made objects. (Pitocchelli, et al., 2012; Pitocchelli, et al., 1997)


Connecticut warblers have been described as a shy, elusive species. These birds are often found walking quietly in their environment and have also been noted hiding within their surroundings. Movements consist of their tail moving up and down as though it is bouncing. The flight patterns of these warblers are similar to those of other warblers in their genus (Oporornis). Although this species is often territorial and solitary, they may form flocks of up to 25 individuals when migrating. Likewise, these birds are known to feed alongside other bird species when they are in their breeding areas. Territoriality exists among male adults. They are the most territorial during the summer and 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 has not been established. These birds maintain territories during the breeding season, although the territory sizes can vary based on their specific habitat. In Minnesota, breeding territories as small as 0.24 ha were noted in open habitats, whereas territories as large as 0.48 ha were seen in more closed habitats. The population density of this species also varies depending on their geographic location. (Pitocchelli, et al., 2012)

Communication and Perception

Connecticut warblers primarily 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 produced 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. Songs are normally heard on breeding grounds, especially during the spring migration period. This species is much quieter during the fall. (Curson, et al., 1994; Pitocchelli, et al., 1997)

Food Habits

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


Anti-predator behavior in this species includes adults distracting predators from their nests by pretending to be injured. Another behavior includes stretching 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 will retreat and skulk into dense shrubbery if they detect one. These birds may respond to intruders and predators near their nests by making scolding calls, which can last up to 30 minutes. The kinds of predators and the manner of predation have not been identified. (Bent, 1963; Curson, et al., 1994; Pitocchelli, et al., 1997)

Ecosystem Roles

Connecticut warblers are victims of brood parasitism by brown-headed cowbirds. The extent of this parasitism still requires study. Other ecosystem roles of this species need to be studied. (Pitocchelli, et al., 1997)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

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

Economic Importance for Humans: Negative

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

Conservation Status

The conservation status of Connecticut warblers is of least concern, although populations are declining. The population size is large enough and is not declining at a rate fast enough to be considered a vulnerable species. Populations may be declining due to over-collecting, as well as habitat loss including forest fragmentation. Conservation methods have not been established 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.



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


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

World Map


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.


a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.


an animal that mainly eats meat


uses smells or other chemicals to communicate


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.

female parental care

parental care is carried out by females


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


an animal that mainly eats fruit


An animal that eats mainly plants or parts of plants.


An animal that eats mainly insects or spiders.


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).


makes seasonal movements between breeding and wintering grounds


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.


an animal that mainly eats all kinds of things, including plants and animals


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

seasonal breeding

breeding is confined to a particular season


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


lives alone


a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.


uses touch to communicate


Living on the ground.


defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement


uses sight to communicate


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 http://www.env.gov.bc.ca/wld/frpa/iwms/documents/Birds/b_connecticutwarbler.pdf.

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 http://bna.birds.cornell.edu.proxy.lib.umich.edu/bna/species/320.

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 http://www.jstor.org/stable/1935753.