Bicknell's Thrush

Bicknell's Thrush
[Bicknell's Thrush - Photo by Henry Trombley]

Bicknell's Thrush (Catharus bicknelli) has been identified as a focal species of management concern because it is one of the rarest (about 25,000-50,000 birds), most range-restricted species in North America. Bicknell's Thrush is confined to high altitude conifer forest habitats found primarily in the far northeastern United States and adjacent areas in Quebec and the Canadian Maritime provinces. Its range and population numbers have declined for several decades, due to loss or degradation of breeding, wintering, and/or migratory stopover habitat. Breeding habitat may have been negatively affected by acid and heavy metal (e.g., mercury) deposition, recreational (e.g., ski area) and industrial (e.g., cellular telephone and wind tower) development, natural disturbances (e.g., spruce budworm outbreaks), and unsustainable timber harvesting. Researchers predict that climate change will significantly reduce available Bicknell's Thrush breeding habitat in coming years, and it could also cause serious changes in natural processes such as timing of prey emergence, and cyclical populations of nest predators. Other threats to the species include collision with man-made structures during migration, and further loss of critical coastal stopover habitat or wintering habitat in the Caribbean.

Date: August 2009

Sources:
International Bicknell's Thrush Conservation Group. Retrieved August 2009 from http://www.bicknellsthrush.org/.

National Audubon Society. The 2007 Audubon WatchList: Bicknell's Thrush. Retrieved August 2009 from http://web1.audubon.org/science/species/watchlist/profile.php?speciesCode=bicthr.

Rimmer, C. C., K. P. McFarland, and W. G. Ellison. 2001. Bicknell's Thrush (Catharus bicknelli). The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology. Retrieved August 2009 from http://bna.birds.cornell.edu/bna/species/592.


Species Profile from NatureServe

Bicknell's Thrush
Catharus bicknelli

Description: A songbird (thrush). Smaller and typically richer brown dorsally than the gray-cheeked thrush; tail color (with various amounts of chestnut) contrasts with the back color in Bicknell's whereas there is little contrast in gray-cheeked thrush; pale area at base of bill is yellowish in Bicknell's, fleshy-pink in gray-cheeked; white of ventral region is duller than in gray-cheeked thrush; songs differ as well, with those of Bicknell's ending on an even or ascending pitch whereas the gray-cheeked's descends (Rimmer et al. 1993, Ouellet 1993). However, Bicknell's thrush from the Gaspe Peninsula lacks bright yellow on the mandible, and some Newfoundland gray-cheeked thrushes have more extensively pale mandibles, "warm" plumage tones, and appear to have a chestnut tail (McLaren 1995). In migration, Bicknell's thrush and gray-cheeked thrush probably cannot be reliably separated without specimens in hand.

Life History: Eggs are laid in June (mostly) and July. Clutch size is 3-6 (average 3-4). Incubation, by female, lasts 12-14 days. Young are tended by both parents, leave nest at 11-13 days. Pairs with failed nests early in the season may renest. Causes of nest failure include predation by red squirrel and blue jay and desertion (Rimmer 1996).

Habitat: In New England and New York, inhabits montane forests, primarily areas dominated by stunted balsam fir and red spruce at elevations above 3000 ft (Rimmer et al. 1993). Habitats in Canada include mountaintop and dense coastal coniferous forests as well as mixed second-growth regenerating stands (Rimmer 1996). In southern Quebec, occurs mainly in second growth stands characterized by relatively young conifers of small size (balsam fir, white spruce) intermixed with a variety of deciduous species typical of second-growth regeneration (PRUNUS sp., BETULA sp., AMELANCHIER sp., ACER SPICATUM, POPULUS sp.) following forest fires or clear cutting; trees seldom exceed 10 m in height (Ouellet 1993). Nests generally are situated close to the trunk in the upper half of a small-to-medium-sized fir or spruce, typically in conifer thickets, often on steep slopes (Rimmer 1996). In migration and winter also in deciduous forest, forest borders, open woodland, second growth, and scrub. Winter habitat may be restricted to primary tropical forest (Rimmer et al. 1993). Occurred at fairly high densities in moist, broad-leafed montane forest in the Dominican Republic (Rimmer 1996).

Palustrine Habitat(s): Riparian

Terrestrial Habitat(s): Forest - Conifer, Forest - Hardwood, Forest - Mixed, Shrubland/chaparral, Woodland - Conifer, Woodland - Hardwood, Woodland - Mixed

Distribution:

United States: CT, DE, GA, MA (extirpated), MD, ME, NC, NH, NJ, NY, PA, RI, SC, VA, VT

Canada: NB, NS, ON, PE, QC

Status:

NatureServe Status: Global Status: G4, Global Status Last Reviewed: 03Dec1996, Global Status Last Changed: 03Dec1996, Rounded Global Status: G4 - Apparently Secure

Other Statuses: Committee on the Status of Endangered Wildlife in Canada (COSEWIC): Special Concern (01Apr1999), IUCN Red List Category: VU - Vulnerable

Resources:

Taxonomy Helper

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Integrated Taxonomic Information System (ITIS)

Bicknells Thrush

    Kingdom: Animalia
    Division: Chordata
    Subdivision: Vertebrata
    Class: Aves
    Order: Passeriformes
    Family: Turdidae
    Genus: Catharus
    Species: Catharus bicknelli
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