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Treetop Brilliance: Blackburnian Warbler
Wednesday May 17, 2017   |
Blackburnian Warbler female by Frode Jacobsen
Provided by American Bird Conservancy

Blackburnian Warblers stand out among warblers for their bright orange and black breeding colors. In fact, they are the only warbler to bear orange coloring on their throats, making them relatively easy to distinguish from the American Redstart — the only other warbler with orange and black plumage.

The species is widely distributed throughout northeastern North America, where it breeds primarily in the eastern half of southern Canada and the northern United States. Individuals are occasionally seen as far west as the Pacific coast and as far east as Bermuda, Tobago, and the Lesser Antilles.

Genetic analysis reveals that the Blackburnian Warbler is most closely related to the Bay-breasted Warbler. The two species overlap throughout much of their range, share approximately 97 percent of their genetic information, and may occasionally hybridize.

Creatures of the Canopy

Most species that share a similar morphology, diet, or other biological traits will avoid competition by geographically separating themselves. This is not the case with warblers. Many warbler species overlap in the same geographic region, where they typically separate themselves based on foraging behavior or ecological niche. Blackburnian Warblers, for example, are creatures of the forest canopy and especially the treetops.

Blackburnian Warblers hunt caterpillars, beetles, spiders, and other small insects on the upper branches of trees — mostly conifers. They are primarily "gleaners" — meaning they seek out and capture prey from foliage and crevices — but they may also capture some insects in flight or by diving or "hawking."

The Migratory Life-cycle

As with many migratory songbirds, Blackburnian Warblers typically travel after nightfall and then settle into habitat to rest and forage during the day. Most fly straight across the Gulf of Mexico, and the earliest arrivals tend to reach the southern United States by March or early April. Once in the United States, the birds may slow their travel speed, sometimes traveling only 25 miles in a single day.

Depending upon their destination, males reach their breeding grounds in mid-April to mid-May, often arriving approximately a week before females. The birds pair almost immediately after arrival on their breeding grounds, and then begin the task of nest building.

Blackburnian Warblers almost always build their nests in the outer reaches of conifer tree limbs, often 10 yards or more above the forest floor. Scientists believe the females build their nests without help from their mates, completing construction of the cup-like structure in approximately three days.

The chicks hatch after approximately 12 days of incubation — by the female only — and remain in the nest until they fledge. The fledglings remain with one or both parents until they can forage successfully on their own, and then sometimes congregate with other fledglings, including those of Black-capped Chickadees.

Blackburnian Warblers — both adults and juveniles — begin their migration south in August or September, often joining larger mixed-species flocks of warblers and other songbirds for the journey. They reach their wintering grounds as early as September or late as November, where they typically forage alone or in small mixed-species flocks.

Deforestation a Concern

With an estimated global population of 14 million, the Blackburnian Warbler is defined as a species of least concern by the International Union for the Conservation of Nature's Redlist. However, individual populations of Blackburnian Warbler may be vulnerable to pressures relating to deforestation and habitat degradation in both their wintering and summering grounds. Because the birds prefer fully forested habitat, their numbers often decline when forests are fragmented by development, logging, or natural causes such as disease. For example, the species has largely disappeared from regions where the balsam woolly adelgid and hemlock woolly agelid — both introduced invasive insect pests — have decimated fir and hemlock forests, including the southern Appalachians as well as some New Jersey, New York, and New England forests.

Deforestation of the Blackburnian Warbler's preferred winter habitat — montane forests in Central and South America — may present a greater threat to the species. The species may benefit from bird-friendly agro-forestry, such as shade-grown coffee or cacao. The warbler occurs in American Bird Conservancy's Santa Marta BirdScape, where we and our partners work to maintain forest and to establish coffee or cacao plantations growing beneath shade trees, providing habitat for the birds.

More at www.abcbirds.org
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