Merlin

Mourning Warbler Life History

Habitat

Habitat Forests

Mourning Warblers live in disturbed or regrowing areas in the boreal forest, where trees are removed and second growth (dense shrubs and saplings) grow quickly. Such areas arise because of storms, fires, and insect outbreaks, and as a result of human activities. Mourning Warbler is thus one of a few migrant bird species that benefit from activities such as logging, mining, oil and gas development, installation of power grids, agriculture, and road building. In their main habitats in the northern part of their range, the dominant trees include aspen, birch, balsam fir, pine, hemlock, and spruce. Mourning Warblers also nest at high elevations in the Appalachian Mountains, where maple, oak, beech, birch, and ash are more prevalent. When trees are lost to fire or other events, shrubs and saplings quickly grow in the disturbed area, among them alder, wild cherry, wild rose, raspberry, blueberry, elderberry, blackberry, chokecherry, cranberry, holly, and hazel. Migrating Mourning Warblers also select similar scrubby habitats when available, and wintering birds in northern South America and southern Central America favor thickets and second-growth forest from moist lowlands up to about 4,600 feet elevation in the Andes. Because breeding habitat becomes unsuitable 7–10 years after a disturbance, as trees begin to dominate shrubs, Mourning Warblers returning in spring must sometimes wander in search of appropriate habitat for nesting. Such wandering birds may occupy marginal habitat for several days before moving on.

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Food

Food Insects

Mourning Warblers eat mostly insects and other arthropods. They forage along branches or in shrubs, usually no more than 10 feet above the ground and more often about 5-6 feet. Here they glean prey from both branches and leaves, eating caterpillars, beetles and their larvae, spiders, and berries. On their wintering grounds in tropical lowlands they may forage lower, occasionally joining groups of birds following swarms of army ants and capturing insects flushed by the ants. When feeding on the ground, Mourning Warblers hop, unlike the similar Connecticut Warbler, which walks (however, Mourning Warblers do walk along branches).

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Nesting

Nest Placement

Nest Ground

The nest is set on or near the ground (rarely more than 3 feet high) in dense shrubs or among ferns or sedges, usually not far from edges in the habitat such as bogs or trails.

Nest Description

The nest is a fairly large, rough cup made of grasses, sedges, weeds, leaves, and bark, then lined with finer grasses, hair, and rootlets. It is likely that the female does all nest construction. Nest measurements average about 6.3 inches across and 3.4 inches tall, with the interior cup 2.1 inches across and 1.9 inches deep.

Nesting Facts
Clutch Size:2-5 eggs
Egg Description:White, speckled with reddish brown and black spots.
Condition at Hatching:Helpless with tufts of dark gray down and red mouth.
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Behavior

Behavior Foliage Gleaner

Mourning Warblers stay low to the ground or deep within shrubby vegetation in dense thickets, giving them a reputation as hard-to-see skulkers. When male Mourning Warblers arrive in suitable breeding areas, they begin establishing a territory by singing frequently and driving away other males, calling loudly, flicking the wings and tail, or chasing the rival. Their flight is swift and darting, similar to that of woodland thrushes and other warblers that live in dense undergrowth. Males sing from low perches, rarely from the ground or the canopy. Near dusk, they also give a flight song, similar to the primary song but including chip notes, sung as they fly upward, then rapidly drop back earthward. Females do not defend nesting territories, which average about 1.75 acres in extent, but both male and female defend the nest against predators, using distraction displays in which they run or fly weakly away from the nest as though injured. Both sexes incubate the eggs and feed nestlings. After the young fledge, some Mourning Warblers remain in breeding areas for several more weeks.

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Conservation

Conservation Low Concern

Mourning Warbler populations declined by about 1.2% annually between 1966 and 2015, resulting in a cumulative decline of 45% over the entire period, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 14 million and rates the species a 12 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. However, the group estimates that if present rates of decline continue, the species will lose another half its population by 2065. Mourning Warblers are particularly susceptible to striking buildings and other structures at night. One study found that Mourning is more than 19 times more likely than the average migrant to collide with low-rise buildings in particular. Mourning Warblers are sensitive to some herbicides, but one study concluded that the negative impacts on the birds are short term.

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Credits

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. (2011). Mourning Warbler (Geothlypis philadelphia), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Sauer, J.R., Niven, D.K., Hines, J.E., Ziolkowski, D.J. Pardieck, K.L., Fallon, J.E., and Link, W.A. (2017). The North American Breeding Bird Survey, Results and Analysis 1966–2015. Version 2.07.2017. USGS Patuxent Wildlife Research Center, Laurel, MD, USA. Available from: https://www.mbr-pwrc.usgs.gov/bbs/bbs.html .

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.

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