Connecticut warbler
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Passeriformes
Family:	Parulidae
Genus:	Oporornis Baird, 1858
Species:	O. agilis
Binomial name
Oporornis agilis (Wilson, 1812)
Range of O. agilis   Breeding range   Winter range

The Connecticut warbler (Oporornis agilis) is a small songbird of the New World warbler family.

These medium-sized warblers measure 13–15 cm (5.1–5.9 in) in length, with a 22–23 cm (8.7–9.1 in) wingspan.^[2][3] Connecticut warblers weigh 10 g (0.35 oz) when they fledge, attaining an average weight of around 15 g (0.53 oz) as adults. However, birds preparing for migration pack on more weight to survive the strenuous journey and can weigh up to 25 g (0.88 oz).^[4][5] This species has light yellow underparts and olive upperparts; they have a light eye-ring, pink legs, a long tail, and a thin pointed bill. Males have a grey hood; females and immatures are more brown and have a whitish throat.

They forage on the ground, picking among dead leaves, or hop along branches. Like most warblers, these birds mainly eat insects and similar small invertebrates. Specifically, they eat spiders, snails, and caterpillars.^[6] They will also supplement their diet occasionally with seeds and berries. They are "skulking" birds that usually spend their time foraging within dense, low vegetation. Such behavior often renders them difficult to see well.

Despite its name, this bird only rarely visits Connecticut during migration. It was named by Alexander Wilson who observed the first classified specimen. They are fairly elusive birds, but it appears that their numbers may be declining due to loss of winter habitat.

Most classification systems consider the genus to be monophyletic. It used to be considered paraphyletic, and it was paired with the mourning, Kentucky, and MacGillivray's warblers in the genus Oporornis. However, recent studies have found that these three warblers were more closely related to the yellowthroats which belong to the genus Geothlypis.^[7]

Their breeding habitat is bogs or open deciduous woods near water, especially with poplar, spruce, tamarack or aspen, in central Canada and states bordering the Great Lakes. These habitats tend to be in rather remote areas that are hard to access for fieldwork; therefore, there is little data available on this species of birds.^[7] The nest is an open cup well-concealed in moss or a clump of grass. It is made of "dry grasses, stalk of weeds, and horsehairs".^[8]

Courtship begins right after the migrants arrive on their breeding grounds. It correlates with the time when males start to sing as this is how they court females. Couples have one brood per season. Connecticut warblers like to nest in thick understory where their young are protected from predators. Most lay in mid-June, though some populations have been observed to lay in July. Their eggs have a creamy color and they are speckled and blotched with chestnut and bay. Only females incubate. Fledglings are observed in late July and at the latest at the end of August. Both parents feed their young caterpillars, larvae, moths, and berries.^[8]

The song of this bird is a loud repeated cheepa-cheepa. It's "similar in pitch to the Kentucky warbler and the Ovenbird".^[9] The call is a nasal pitch, it sounds like a raspy "witch". Like many songbirds, its song is heard during the breeding season but rarely during the fall.^[9]

The Connecticut warbler walks on the ground to forage insects and other sources of food. Its tail bobs up and down, which is reminiscent of wren and sandpiper behaviour.^[7] When it comes to sociability, the Connecticut warbler is a solitary species; however, groups of about twenty-five will come together in the fall before migration. It also will join other species, such as Blackpoll warblers, to feed during the fall.^[10] Males are highly territorial during breeding season, they defend an area which ranges from 0.24–0.48 hectares.^[7]

When it comes to parental care, both the male and the female will feed the juvenile.^[6] They will defend their young by screeching at predators.

As mentioned earlier, the Connecticut warbler is an elusive species. Little is known about it outside of the breeding season as to this date, less than 25,000 individuals have been banded.^[11] These birds migrate to the Amazon Basin in South America in winter. Specimens have been observed in Colombia (north & southeast), Venezuela (northeast & interior), Guyana (at the border), and Peru (South).^[11] Connecticut warblers undertake different migratory routes in spring and in fall, an atypical behavior. In spring, they normally pass through the Midwest and only rarely migrate to the East Coast, but in fall, larger numbers of migrating birds move through the East Coast. Recently, the use of small tracking devices has enabled scientists to gather more data on the warbler's migration routes. They have discovered some individuals fly over open water like the Blackpoll warbler. More specifically, they recorded a previously undocumented two-day flight over the Caribbean to the Antilles.^[11] This correlates with sightings of Connecticut warblers that have occurred in Bermuda, St. Thomas and St Martin. Haiti on the island of Hispaniola is also a popular stop, but records there are hard to find due to the terrain being rather remote and past humanitarian crises; it is also additionally threatened by the ongoing deforestation in both Haiti and the Dominican Republic.^[11] There, they make a minimum of 48-hour stop (it usually lasts 5–7 days) in the Caribbean. This long migration over open water calls for strong selective pressures. A comparative study between the Connecticut warbler and the blackpoll warbler could help determine what selective pressures are present in these two species. This kind of migration also demands large reserves of fuel and this is why fat Connecticut warblers can be found on the East Coast in early fall.^[11] It's also the reason why they make several stopovers on their way South.

One of the main causes of mortality during migration is the collision of individuals into man-made structures. Collisions often occur against transparent glass panes, through which individuals can see vegetation and light.^[7] Habitat destruction is another threat to Connecticut warbler populations. Aspen logging on their breeding range (i.e. BC) and the application of pesticides get rid of nesting locations. The infestation of budworms on jack-pine trees also puts nesting sites at risk. The presence of power lines is also a danger to the Connecticut warbler: studies show that the presence of power lines reduces population densities in areas where they are present.^[12] In Alberta breeding sites, noise disturbances from gas pipelines are detrimental to the species as well.^[13] Studies show that Connecticut warblers did well in forests that have been cleared off of shrubs and understory as they prefer trees; however, their abundance decreased in areas where the forest was clear-cut.^[13] Connecticut warblers are on the IUCN red list as a species of Least Concern.^[14] Nevertheless, some of its populations in Saskatchewan, Michigan, Minnesota, and Wisconsin are at risk. Conservation efforts are difficult due to a lack of research, though a handful of researchers have written some management plans, focusing on the preservation of woody wetlands, which are the Connecticut warbler's favored habitat.^[13]

• Pitocchelli, J., J. Bouchie, and D. Jones. 1997. Connecticut Warbler (Oporornis agilis). In The Birds of North America, No. 320 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D.C.

• Cooper JM, Enns KA & Shepard MG. (1997). Status of the Connecticut warbler in British Columbia. Canadian Research Index. p. n/a.

• Bosque, Carlos; Lentino, Miguel (1987). "The Passage of North American Migratory Land Birds Through Xerophytic Habitats on the Western Coast of Venezuela". Biotropica. 19 (3): 267–273. Bibcode:1987Biotr..19..267B. doi:10.2307/2388346. JSTOR 2388346.
• Lind, Jim; Danz, Nicholas P.; Hanowski, JoAnn M.; Niemi, Gerald J. (2003). Breeding Bird Monitoring in Great Lakes National Forests : 1991-2003 (Report). University of Minnesota Duluth. hdl:11299/200711.
• Elder DH. (1991). Breeding Habitat of the Connecticut Warbler in the Rainy River District. Ontario Birds. vol 9, no 3. pp. 84–86.
• Ferguson RS. (1981). Summer Birds of the Northwest Angle Provincial Forest and Adjacent Southeastern Manitoba Canada. Syllogeus. vol 31, pp. 1–23.
• Hall D. (1995). On rarity and mischance. The Yale Review. vol 83, no 2. p. 74.
• Hobson, Keith A.; Schieck, Jim (August 1999). "Changes in bird communities in boreal mixedwood forest: Harvest and wildfire effects over 30 years". Ecological Applications. 9 (3): 849–863. doi:10.1890/1051-0761(1999)009[0849:CIBCIB]2.0.CO;2. JSTOR 2641334.
• Jahn O, Viteri MEJ & Schuchmann K-L. (1999). Connecticut Warbler, a North American migrant new to Ecuador. Wilson Bulletin. vol 111, no 2. pp. 281–282.
• Machtans CS. (2000). Extra-limital observations of Broad-winged Hawk, Buteo platypterus, Connecticut Warbler, Oporornis agilis, and other bird observations from the Liard Valley, Northwest Territories. Canadian Field-Naturalist. vol 114, no 4. pp. 671–679.
• McCaskie G. (1970). Occurrence of the Eastern Species of Oporornis and Wilsonia in California. Condor. vol 72, no 3. pp. 373–374.
• McKenzie PM & Noble RE. (1989). Sight Records for Connecticut Warbler Oporornis-Agilis and Yellow-Throated Vireo Vireo-Flavifrons in Puerto Rico USA. Florida Field Naturalist. vol 17, no 3. pp. 69–72.
• McNair DB, Massiah EB & Frost MD. (1999). New and rare species of Nearctic landbird migrants during autumn for Barbados and the Lesser Antilles. Caribbean Journal of Science. vol 35, no 1–2. pp. 46–53.
• Morgan JG & Eubanks TLJ. (1979). Connecticut Warbler Oporornis-Agilis New-Record in Texas USA. Bulletin of the Texas Ornithological Society. vol 12, no 1. pp. 21–22.
• Niemi, Gerald J.; Hanowski, JoAnn M. (1984). "Effects of a Transmission Line on Bird Populations in the Red Lake Peatland, Northern Minnesota". The Auk. 101 (3): 487–498. doi:10.1093/auk/101.3.487. JSTOR 4086601.
• Parker, Theodore A. (1982). "Observations of Some Unusual Rainforest and Marsh Birds in Southeastern Peru". The Wilson Bulletin. 94 (4): 477–493. JSTOR 4161674.
• Parmelee DF & Oehlenschlager RJ. (1972). Connecticut Warbler Nest in Hubbard County Minnesota. Loon. vol 44, no 1. pp. 5–6.
• Rogers TH. (1982). The Spring Migration March 1 – May 31, 1982 Northern Rocky Mountain Intermountain Region Canada USA. American Birds. vol 36, no 5. pp. 875–877.
• Schulte, Lisa A.; Niemi, Gerald J. (1998). "Bird Communities of Early-Successional Burned and Logged Forest". The Journal of Wildlife Management. 62 (4): 1418–1429. doi:10.2307/3802008. JSTOR 3802008.
• Shanahan D. (1992). Notes on calls of breeding Connecticut warblers. Ontario Birds. vol 10, no 3. pp. 115–116.
• Shier GR. (1971). 1st Fall Record of the Connecticut Warbler in Colorado. Colorado Field Ornithologist. vol 10, pp. 19–20.
• Thomas, Betsy Trent (1993). "North American Migrant Passerines at Two Non-Forested Sites in Venezuela (Paseriformes migratorios en dos localidades no-forestadas de Venezuela)". Journal of Field Ornithology. 64 (4): 549–556. JSTOR 4513867.
• Venier, L. A.; McKenney, D. W.; Wang, Y.; McKee, J. (1999). "Models of large-scale breeding-bird distribution as a function of macro-climate in Ontario, Canada". Journal of Biogeography. 26 (2): 315–328. Bibcode:1999JBiog..26..315V. doi:10.1046/j.1365-2699.1999.00273.x. JSTOR 2656117.
• Welsh, Daniel A.; Venier, Lisa A. (1996). "Binoculars and satellites: developing a conservation framework for boreal forest wildlife at varying scales". Forest Ecology and Management. 85 (1–3): 53–65. Bibcode:1996ForEM..85...53W. doi:10.1016/S0378-1127(96)03750-4.

• Connecticut Warbler Species Account – Cornell Lab of Ornithology
• Connecticut Warbler – Oporornis agilis – USGS Patuxent Bird Identification InfoCenter