Townsend's Warbler Life History

Habitat

Habitat Forests

Townsend’s Warblers breed in mature coniferous and mixed woodlands, especially old-growth fir forest with extensive understory, and in spruce and hemlock forests in the northern parts of their range. They nest from sea level through subalpine forests, so long as trees are tall, but are uncommon in logged forests. In migration, Townsend’s Warblers use habitats including willow-alder thickets along waterways, coniferous woodlands, orchards, juniper-oak woodlands, aspen forests, riparian cottonwoods, gardens, parks, and oases of almost any sort in desert environments. Wintering birds also accept many different habitat types. Birds that winter in California favor live oaks and mixed oak-coniferous woodlands, chaparral, and suburban parks. Much of the population winters in Middle America, usually in montane forests with a mixture of oak and conifers, from middle elevations to cloud forest.

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Food

Food Insects

During the breeding season Townsend’s Warblers pluck insects and their larvae from conifer needles and buds and occasionally catch flying insects in midair. Adults forage in the forest canopy most often, but may come lower down when feeding young. Townsend’s eat caterpillars—especially spruce budworms—as well as ants, bees, moths, beetles, weevils, and bugs (especially stinkbugs). Spiders, seeds, and leaf galls form a smaller portion of the diet. During migration, they feed in flowers, apparently taking the nectar. In some wintering locations they feed in oaks on the “honeydew,” or sugary digested sap excreted by scale insects. Birds that visit backyard feeders take mealworms, peanut butter, and suet.

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Nesting

Nest Placement

Nest Tree

The female checks several sites, then thoroughly investigates the chosen nest site by probing the foliage. Nests are set in conifers, usually in larger spruce or fir, on a main limb at an average height of 36 feet above ground.

Nest Description

The female builds the nest, a bulky cup made of bark, conifer needles, twigs, plant fibers, grass, lichens, and spider cocoons, lined with grass, moss stalks, and hair. Nest dimensions vary widely but average roughly 4 inches across and 3 inches tall, with interior cup 2.4 inches across and 1.5 inches deep.

Nesting Facts
Clutch Size:3-7 eggs
Number of Broods:1 brood
Egg Length:0.7-0.7 in (1.67-1.77 cm)
Egg Width:0.5-0.5 in (1.26-1.35 cm)
Incubation Period:11-14 days
Nestling Period:9-11 days
Egg Description:

White with brown speckles.

Condition at Hatching:

Helpless with tufts of down.

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Behavior

Behavior Foliage Gleaner

Male Townsend’s Warblers arrive on breeding grounds earlier than females and establish territories, often battling for days with rivals before territorial boundaries are set. Pairs form quickly, but a specific courtship display has not been described. Males follow females closely during nest-building and egg-laying, occasionally lowering the head and flaring the wings and tail feathers, a courtship display that also resembles the threat display they use toward males intruding into the territory. Both males and females chase intruders from the territory, which is used both for nesting and foraging. They also sometimes chase other species of warblers or sparrows away from the nest after the young have hatched. Townsend’s Warblers are thought to have a monogamous mating system, although observations of up to three “additional” males near newly paired females imply that mating outside the pair probably occurs to some extent. Both sexes feed and tend the young.

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Conservation

Conservation Low Concern

Townsend’s Warbler populations were roughly stable or slightly declining between 1968 and 2015, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 21 million and rates the species a 12 out of 20 on the Continental Concern Score, indicating it is a species of low conservation concern. Habitat loss may be an issue for this species, both on the wintering grounds and especially on the nesting grounds, where logging reduces the amount of old-growth and mature fir forests on the landscape. Fragmentation of forests may also expose the birds to more predators. Townsend’s Warblers, like most songbirds that migrate nocturnally, often die when they strike buildings and other structures.

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Backyard Tips

On the Pacific coast in winter, Townsend’s Warblers often investigate backyard feeders, most regularly when temperatures drop below freezing, to eat energy-rich foods such as mealworms, peanut butter, and suet.

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Credits

Fleischman, P. 1992. Townsend’s Warbler. HarperCollins, New York.

Lutmerding, J. A. and A. S. Love. Longevity records of North American birds. Version 2015.2. Patuxent Wildlife Research Center, Bird Banding Laboratory 2015.

North American Bird Conservation Initiative. (2014). The State of the Birds 2014 Report. US Department of Interior, Washington, DC, USA.

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

Sauer, J. R., J. E. Hines, J. E. Fallon, K. L. Pardieck, Jr. Ziolkowski, D. J. and W. A. Link. The North American Breeding Bird Survey, results and analysis 1966-2013 (Version 1.30.15). USGS Patuxtent Wildlife Research Center (2014b). Available from http://www.mbr-pwrc.usgs.gov/bbs/.

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

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

Wright, A. L., G. D. Hayward, S. M. Matsuoka and P. H. Hayward. (1998). Townsend's Warbler (Setophaga townsendi), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

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