Mourning Warbler

Quick Take

• This tiny warbler pulls off a predator trick so convincing it can fool even experienced naturalists, and the technique does not involve hiding. See the deception tactic →
• Mourning Warblers actually thrive in habitats most birds avoid, a trait that may be the key to their survival in a changing landscape. Explore habitat adaptability →
• Two warblers look nearly identical, share part of the same continent, and even experts struggle to separate them. So what is the real difference? Compare the look-alikes →
• Mourning Warbler chicks leave the nest faster than almost any comparable songbird, and the reason behind this reveals something counterintuitive about ground-nesting survival. Discover fledgling timing →

The Mourning Warbler is a member of the Parulidae family of New World or wood warblers. It breeds primarily in Canada and the far northeastern United States, including the Great Lakes region and New England. It migrates through the eastern United States, from the Great Plains to the coast, and along eastern Mexico and parts of the Caribbean to its wintering grounds in Central America and parts of far northwestern South America. This little yellow-bellied bird with a gray hood is often mistaken for its lookalike, the MacGillivray’s Warbler, which inhabits the western part of North America. In the narrow region where the range of these two warblers overlaps, only skilled birdwatchers can tell them apart.

Incredible Mourning Warbler Facts

• The Mourning Warbler was first described by Alexander Wilson, who collected a specimen in Philadelphia.
• These birds use deception to fool predators, sometimes even pretending to have a broken wing to lure them away from the nest.
• Mourning Warblers may be mistaken for MacGillivray’s Warblers based on appearance, but their ranges mostly do not overlap.
• These warblers nest on the ground or just a foot or two above, in dense thickets.
• Like many ground-dwelling birds, Mourning Warblers leave the nest quickly, after just 7 to 9 days.
• Squirrels are among the most common predators of these birds.

Where to Find Mourning Warblers

Mourning Warblers can be found primarily in the eastern half of Canada and the United States, and south to Central America and far northwestern South America. Their breeding grounds are mainly in southeastern Canada and the northeastern part of the United States. Their range extends as far west as the Great Plains states in the U.S. and as far west as Alberta and a small pocket of British Columbia in Canada. Few confirmed sightings have occurred within or west of the Rocky Mountains.  

Migration routes take Mourning Warblers south through the eastern half of the United States and far eastern Mexico. The birds also migrate through parts of the Caribbean and Central America. They eventually arrive at their winter grounds in northern Central America, including Costa Rica and Panama, and far northwestern South America, including parts of Ecuador, Colombia, and Venezuela.

The Mourning Warbler nests and spends most of its time on or near the ground. As such, it prefers disturbed or burned forests with dense undergrowth, or clearings with dense shrubs, briars, or woody thickets in its breeding areas. It also frequents forest edges and cultivated fields or thick grassy areas.

On their winter grounds, these warblers prefer to stay in low-lying areas with access to fresh water. They require plenty of vegetation within which they can forage. The Mourning Warbler also eats fruits from the trees in its winter habitat.

Nests

These birds build cup-like nests on or near the ground. The nests may be placed directly on the ground, usually hidden under a thicket, or one or two feet off the ground in dense vegetation. The nests themselves are made of leaves, grass, and weeds. The warblers line the nests with hair or fine grasses.

Classification and Scientific Name

The Mourning Warbler’s scientific name is Geothlypis philadelphia. It was first described in 1810 by the ornithologist and poet Alexander Wilson, three years before his death. He collected a single specimen in Philadelphia and, naming it for the city, called it Sylvia philadelphia. The genus Sylvia included several different warblers at that time. It was later moved to the genus Oporornis along with a few other warblers based on appearance and behavior. By 2011, all but one of these were reassigned to the Geothlypis genus based on genomic results.

Geothlypis means ground bird and is a reference to the tendency to live and nest on or near the ground. This genus includes more than a dozen warbler species known as the yellowthroats.

Appearance

The Mourning Warbler’s common name is a reference to the gray plumage on its head and neck. This coloration resembles a mourning veil and is a defining characteristic of the bird. Males have a strong, black patch at the base of their gray hood, where it meets the bright yellow breast. This black patch is shaped like a wide crescent, open toward the head. They also have a black eye line running from the top of the bill to the eye. Immature males have a yellow throat and black speckles, where their black patch will eventually fill in. Females lack these black markings and have lighter gray hoods.

Mourning Warblers are small birds averaging about 5.2 inches in length with a wingspan of 7.5 inches. They weigh approximately 0.45 ounces. Both sexes have olive feathers on their upper body and bright yellow on their underparts. Their beaks are pinkish, though those of adult males are tinged with black. They have pink legs and delicate feet with three toes facing forward and one facing back.

Behavior

The Mourning Warbler is diurnal, but most active in the early morning and near dusk. Because it lives so near the ground, and usually in thick vegetation, it is adept at hiding. It flits from branch to branch or stem to stem and tends to hop along the forest floor rather than walk. However, when threatened, it may scurry like a mouse to distract predators away from its nest.

Mourning Warblers forage quietly for insects and other prey among the leaf litter on the forest floor. Females do not sing, but males do. Males fly up to higher branches in trees to sing their songs, especially during the breeding season. They can usually be heard before mid-morning and as twilight approaches in the evening. They have a two-syllable call that they usually repeat four or five times, descending in pitch at the end. In Wilson’s description of the bird, he wrote that it “had a sprightly and pleasant warbling song, the novelty of which first attracted my attention.” Other observers have described the song as sounding like “chirry-chirry-chirry-chorry-chorry.”

Mourning Warblers are somewhat territorial. Multiple adults may nest within the same territory, which covers about two acres, and males will actively defend it. They mainly use a territorial “tshrip” call to warn other birds away, along with posturing including aggressive bobbing and wing flapping. Females also use the territorial call and behaviors when defending the nest.

Migration

Mourning Warblers migrate each year, from their breeding grounds in the north to their winter grounds to the south and back again. They arrive late in the season, sometimes as late as June, to their breeding grounds in Canada and the northeastern United States. The timing of their arrival depends on the weather: they show up by late spring in warm years and in summer in colder years. They migrate south to Central and South America in the fall, leaving sometime between late August and early November. Again, the timing of their migration likely depends on the seasonal weather.

Because these warblers prefer to nest in disturbed forests in the early stages of regrowth, they may not be able to return to the same territory when migrating back to their breeding grounds. As forests mature, the dense undergrowth that the birds rely on can disappear. Therefore, it may take longer for Mourning Warblers to find suitable nesting locations and establish new territories than many other migratory songbirds.

Diet

Mourning Warblers are omnivorous birds. They eat fruits, particularly on their wintering grounds, but their diet consists mostly of insects and other invertebrate prey. They eat both mature insects and insect larvae, spiders, and possibly other arthropods. These birds forage mainly on the forest floor or beneath thickets, using their pointy beaks to capture prey. They also sometimes catch insects on the wing. Interestingly, they tend to rip the legs and wings off their prey before consuming them.

According to reports from the field, nestlings are fed mainly larvae from butterflies and moths, although parents feed them other insects as well. Although the young leave the nest after only about one week, the parents continue to provide food and care for about a month after fledging.

Reproduction

Mourning Warblers reach sexual maturity after approximately one year. They build cup-shaped nests of leaves, grass, and weeds on the ground, usually within a thicket that will provide cover. Sometimes they build their nests a foot or two off the ground in dense vegetation. They lay an average of 2 to 5 eggs and have just one brood per year. The female incubates the eggs alone for 12 days, while the male guards the territory. Both parents feed the chicks during the short nestling period. They fledge after just 7 to 9 days, but the parents continue to care for the young for up to four weeks after fledging.

Predators

Forest-dwelling birds, such as Mourning Warblers, are vulnerable to birds of prey such as owls and hawks. They are also vulnerable to predation by domestic cats. The most common nest predators of these particular warblers are different types of squirrels, including ground squirrels and red squirrels, chipmunks, and raccoons.

Mourning Warblers employ a couple of clever methods to distract predators from their nests. Females incubating eggs will remain on the nest as a predator draws near, sitting quietly as long as possible to avoid detection. If exposure is unavoidable, they will leave the nest and scurry quickly on the ground, moving much like a mouse, until they are at least 20 or 25 feet away before flying to safety. Both males and females also distract predators by pretending to have a broken wing, dragging it along the ground to draw the predator’s attention and lure it away from the nest.

Lifespan

The oldest recorded Mourning Warbler in the wild was 7.9 years old. There is little information regarding the average lifespan of these birds. With an estimated population of approximately 14 million mature adults, the IUCN Red List for Threatened Species lists the Mourning Warbler as a species of least concern. Their population is believed to be moderately declining. Researchers believe that the bird’s natural tendency to use disturbed or burned forests may allow it to thrive in fragmented habitats where many other birds have struggled.