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Connecticut Warbler Life History



Connecticut Warblers breed in forests in central Canada and around the western Great Lakes where most of these woodlands have an open quality, such as poplar forests or spruce bogs. Many of their breeding habitats are wet, with stands of willow, dogwood, or alder, and abundant ground cover that may include ferns, raspberries, labrador tea, bog laurel, leatherleaf, and sphagnum mosses. In some breeding areas, fir, tamarack, larch, birch, aspen, and white cedar are prevalent as well. However, some Connecticut Warblers do breed in drier habitats such as jack pine barrens and pine-oak forests. Breeding territories typically include dense undergrowth, edges, vine tangles, and forest gaps. Migrants also gravitate toward similar complex habitats, especially damp woodlands with dense undergrowth. Wintering birds in South America occupy woodlands, forest edge, and dense, shrubby second growth, usually below 6,600 feet elevation. Ornithologists have not determined their primary wintering habitat type and have been surprised to find them in habitats as varied as dry woodland, second growth, tropical rainforest, cloud forest, and even paramo—a high-elevation habitat that lacks tall trees. Some of these records could refer to migrants rather than wintering birds.

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Connecticut Warblers eat mostly insects, spiders, and other arthropods. They walk slowly along the ground, sometimes probing in the ground or in leaf litter with their heavy bill. When insects, including larvae and eggs, are abundant in trees, Connecticut Warblers also forage well above the ground, even in treetops. Migrants sometimes join mixed-species flocks, but most reports are of solitary birds during migration. Connecticut Warblers also occasionally eat berries such as raspberries and some seeds.

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Nest Placement


The nest is made on the ground or very close to the ground, in dense undergrowth, often in thickets or at the base of a bush, and normally well hidden by the undergrowth. Less often, they nest in weedy fields well away from forest edges.

Nest Description

The nest is a cup of grasses, leaves, weeds, sedges, fine roots, and hair such as horsehair. Nest measurements, seldom reported, average 5 inches across and 2.2 inches tall, with the interior 2 inches across and 1.5 inches deep.

Nesting Facts

Clutch Size:3-5 eggs
Number of Broods:1 brood
Egg Length:0.7-0.8 in (1.76-2.02 cm)
Egg Width:0.5-0.6 in (1.38-1.52 cm)
Egg Description:Creamy white with dark speckles.
Condition at Hatching:

Naked and helpless.

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Ground Forager

Little is known about Connecticut Warblers on the breeding grounds. Males are territorial, defending breeding territories of up to 1.25 acres by countersinging with and chasing rival males in flight or on foot, or walking along horizontal limbs with pumping tail and jerky gait. In flight, Connecticut Warblers are remarkably swift, recalling thrushes in both shape and movement. Both parents feed the young at the nest, which is built directly on the ground and well concealed. Parents bringing food back to the nest land as much as 50 feet away from the nest, then walk to the nest underneath the ground cover. Foraging birds walk on the ground much like an Ovenbird or Spotted Sandpiper, occasionally bobbing the short tail as they proceed. Family groups stay together for several weeks after the young fledge and occasionally gather with other family groups before migration.

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According to the North American Breeding Bird Survey, Connecticut Warbler populations declined by about 2% per year between 1966 and 2015, suggesting a cumulative decline of 62% in that period. However, most of the population breeds in remote parts of central Canada, beyond the reach of the Breeding Bird Survey, so these numbers may not reflect trends in the entire population. Partners in Flight estimates a global breeding population of 1.8 million, rates the species a 13 out of 20 on the Continental Concern Score, and includes the species on the Yellow Watch List for declining populations. Although few studies have been conducted, Connecticut Warblers are vulnerable to some forestry practices that decrease available habitat, including logging, application of herbicides, and fire suppression, as well as fragmentation of habitat associated with forestry, oil and gas development, construction of power transmission corridors, and agriculture. The species’ habitat requirements on the wintering grounds are little studied, but it is likely that deforestation has reduced available habitat there.

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Lutmerding, J. A., and A. S. Love (2017). Longevity records of North American birds. Version 2017.1. Patuxent Wildlife Research Center, Bird Banding Laboratory, Laurel, MD, USA.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Pitocchelli, Jay, Julie Jones, David Jones and Julie Bouchie. (2012). Connecticut Warbler (Oporornis agilis), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2017). The North American Breeding Bird Survey, Results and Analysis 1966–2015. Version 2.07.2017. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

Stephenson, T. and S. Whittle (2013). The Warbler Guide. Princeton University Press, New Jersey, USA.

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