Merlin

Blackburnian Warbler Life History

Habitat

Habitat Forests

Blackburnian Warblers select mature coniferous and mixed coniferous-deciduous forests, though in Virginia and North Carolina, the southernmost part of their breeding range, they may nest in pure deciduous forest. Red, white, and black spruce forests across the southern edge of the boreal forest belt have nesting populations, as do forests containing balsam fir, white pine, and yellow birch. Singing males often select song perches at the very tips of the tallest spires of spruce or balsam fir, making them easy to locate in such habitats. During autumn migration, Blackburnian Warblers can be found in waves of migrant warblers on well-forested mountainsides, among many other species, as they move rapidly up or down slopes in search of insect prey to fuel their continued migration. In lowlands, migrants may turn up in many different sorts of wooded habitats, even relatively low-stature second growth or edges. On the coast, Blackburnians are sometimes seen foraging near the ground in shrubs, if no taller habitat is available. Spring migrants may also be found in many sorts of habitat, especially if they have just descended from nocturnal migration and have not yet oriented to their surroundings. “Fallouts” of the species on the Gulf of Mexico coast or the shores of Lake Ontario are not uncommon; newly arrived migrants can sometimes be seen foraging on lawns or shorelines at such times. On the wintering grounds in tropical America, Blackburnian Warblers inhabit foothills and highlands above 3,000 feet, mostly in northwestern South America, on both sides of the Andes. Here they can be found in a tremendous range of habitat types: rain and cloud forests, second growth of many kinds, shade-coffee plantations, and dwarf forest. Most forage in the canopy here, but if competition from other warblers is low, they forage from eye level up into the treetops.

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Food

Food Insects

As is true of other warblers that nest in the short breeding season in coniferous forests, Blackburnian Warblers eat large quantities of caterpillars, including those of the abundant spruce budworm. They also eat spiders and larval and adult flies, mayflies, beetles, leaf-rollers, ants, aphids, scale insects, and lacewings. Most of their prey is captured by gleaning or hover-gleaning; they also probe needle clusters or clumps of dead leaves. Blackburnian Warblers occasionally take fruit (berries) as well.

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Nesting

Nest Placement

Nest Tree

Nests are typically in dense foliage near the far end of a limb high in a coniferous tree, though nests in deciduous trees have been recorded as well, especially in the southernmost part of the breeding range. Their nests are usually higher in the tree than those of other warbler species, up to 80 feet high, but rare nests have been found as low as just 4 feet.

Nest Description

Females build a cup-shaped nest of twigs, bark, rootlets, and fibers, secured to the branch with spider silk. The cup is lined with lichens, moss, fine grass, hair, and conifer needles, occasionally with plant down. Nests are about 3.2 inches wide by 1.8 inches tall, with the interior of the cup 2 inches wide by 1 inch deep.

Nesting Facts
Clutch Size:3-5 eggs
Number of Broods:1 brood
Egg Length:0.6-0.7 in (1.5-1.8 cm)
Egg Width:0.4-0.5 in (1.1-1.3 cm)
Incubation Period:12-13 days
Egg Description:White or greenish white with brown spots and blotches.
Condition at Hatching:Helpless with tufts of down.
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Behavior

Behavior Foliage Gleaner

Males arrive on the nesting ground before females and sing through the day to advertise to potential mates. Conflicts between males are common at this time, with aggressive displays that appear almost comical in their choreography, with pirouetting moves, bill snapping, wing flicking, and many sorts of flamboyant aerial clashes. They also deliver warnings by singing a different song or by singing very quietly. During the nesting season, males keep up their singing in the early morning or early evening using favored song perches to mark territory. They quickly chase intruding male Blackburnians from the territory. Territories range in size from 1 to 3 acres, and both male and female tend to remain within the boundaries of the territory while raising young. So far as is known, Blackburnian Warblers have a brief courtship display: the female flutters her wings, spreads her tail, and crouches, and the male responds with gliding flights and song. Females apparently construct the nest and do most of the incubation; both sexes feed nestlings and fledglings. Parents remain with fledglings for a brief time after they leave the nest; all members of the family may join local mixed flocks led by Black-capped Chickadees.

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Conservation

Conservation Low Concern

Blackburnian Warbler populations appear to be stable, according to the North American Breeding Bird Survey. Partners in Flight estimates a 10% increase since 1970 and a global breeding population of 14 million birds. The species rates a 9 out of 20 on the Continental Concern Score indicating it is a species of low conservation concern. Deforestation via logging is a major concern in both the breeding and wintering ranges for Blackburnian Warblers and for numerous other Neotropical migrant birds. In places where spruce budworm control involved heavy use of pesticides such as fenitrothion, populations of Blackburnian Warbler and other warblers were reduced. Losses of Fraser firs in the southern Appalachians from the introduced balsam wooly adelgid has led to the disappearance of Blackburnian Warblers in many southern parts of its range. The same is true in hemlock forests from New Jersey to New England, where trees have succumbed to hemlock wooly adelgid.

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Backyard Tips

If your backyard has plenty of trees, you might attract Blackburnian Warblers on migration or in summer. They may remain hard to find in the tree canopy, but they may come down into view if you offer a bird bath or water dripper. See more ideas for creating water features in your yard. Warblers don’t come to seed feeders, although they may stop by if you offer mealworms.

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Credits

Dunn, J. L., and K. L. Garrett. (1997). A Field Guide to the Warblers of North America. Houghton Mifflin Company, Boston, MA, USA.

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

Morse, Douglass H. (2004). Blackburnian Warbler (Setophaga fusca), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, 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.

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