Arctic Warblers in Alaska breed in brushy areas, often in dwarf willows, which grow in wet areas and near streams. Stands of shrub birch or stunted white spruce also provide foraging and breeding habitat. In some parts of the range, Arctic Warblers nest in areas that have patches of taller vegetation interspersed with meadows of sedges, grasses, flowering plants, and forbs, such as soapberry, wormwood, anemones, or arctic aster. Arctic Warblers that nest in Alaska migrate to the Philippines, where they inhabit just about any habitat—from lowland forests, plantations, edge habitats, gardens, and mangroves to rainforests as high as 4,000 feet in elevation.Back to top
Arctic Warblers eat mostly insects. Like all leaf warblers, they flit through shrubs and trees, gleaning insects from leaves and twigs. Most of their foraging occurs near the tops, between 6 and 32 feet above the ground—though on the breeding grounds, where vegetation is shorter, they forage mostly below 20 feet. On occasion, they forage on the ground, on invertebrates they find at the water’s edge, and sometimes, they catch flying insects in the air. Arctic Warblers often contort their bodies and necks while inspecting leaf surfaces, and they twitch their wings quickly, perhaps to startle prey into moving. Prey includes many types of flies, mayflies, stoneflies, caddisflies, grasshoppers, booklice, beetles, bugs, and larval moths and caterpillars; they also eat millipedes, spiders, harvestmen, fairy shrimp, and tiny snails. Back to top
Nests are set on the ground (on grasses or moss) near willows or other small trees or shrubs.
Both male and female build a domed nest of grasses, mosses, and leaves, and line it with fine grass and hair. The entrance hole to the nest is on the side. Nests average about 4.7 inches across and 4 inches tall, with a nest cup 2.5 inches across and 2 inches deep.
|Clutch Size:||5-7 eggs|
|Egg Description:||White with russet spots, denser at larger end.|
|Condition at Hatching:||Naked and helpless.|
Immediately on their return to Alaska from wintering grounds in the Philippines, male Arctic Warblers begin to establish breeding territories, singing incessantly while foraging during the long days of June and July. Males also sing to attract females, which arrive slightly later. Males defend territories of about 4 acres, and while establishing territorial boundaries often clash, chipping and singing at each other at close range, fluffing up their crown, rump, and throat feathers, and flicking their wings. Males usually partner with one female (occasionally two) during the breeding season. Females indicate interest in singing males by flapping and rattling the wings. Males may respond with raised, rattling wings, puffed up plumage, and raised tail, often chasing the female as well. A receptive female accepts caterpillars from the male, a display called courtship feeding. Both male and female share incubation and chick-rearing duties. Adults feed fledged young for a week or more as they prepare for autumn migration. Migrants frequent many different sorts of habitats, even including low patches of weeds. On wintering grounds, Arctic Warblers do not form flocks and are not obviously territorial. Back to top
Partners in Flight estimates a global breeding population of 82 million, with perhaps 2.5 million breeding in Alaska, and rates Arctic Warbler 10 out of 20 on the Continental Concern Score. However, the Alaska population has declined steeply in the last 30 years, prompting Partners in Flight to place the species on its Common Birds in Steep Decline list. Loss of habitat on wintering grounds is of concern, and global climate change will alter their breeding habitat.Back to top
Lowther, Peter E. and Susan Sharbaugh. (2014). Arctic Warbler (Phylloscopus borealis), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.
Lutmerding, J. A. and A. S. Love. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.
Partners in Flight. (2020). Avian Conservation Assessment Database, version 2020.
Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.