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Bicknell's Thrush
Catharus bicknelli
Order
PASSERIFORMES
– Family
TURDIDAE
Authors: Rimmer, Christopher C., Kent P. McFarland, Walter G. Ellison, and James E. Goetz
Revisors: Rimmer, Christopher C., Kent P. McFarland, and Jason Townsend

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Introduction

Adult Bicknell's Thrush, Ullster Co., NY, 17 June.
Figure 1. Distribution of Bicknell’s Thrush.

The song is in a minor key, finer, more attenuated, and more under the breath than that of any other thrush. It seemed as if the bird was blowing in a delicate, slender, golden tube, so fine and yet flute-like and resonant the song appeared. At times it was like a musical whisper of great sweetness and power. Burroughs 1904: 51.

. . . only a freak ornithologist would think of leaving the trails [on Mt. Mansfield] for more than a few feet. The discouragingly dense tangles in which Bicknell’s Thrushes dwell have kept their habits long wrapped in mystery. Wallace 1939: 285

Bicknell’s Thrush inhabits areas that humans do not. The species is found exclusively in remote, inhospitable montane and maritime forest habitats, and its penchant for dawn and dusk activity underscore its status as one of the most reclusive breeding birds in North America. It is also among the most rare and, possibly, most threatened. The Bicknell’s Thrush breeding range consists of fragmented islands of habitat from the northern Gulf of St. Lawrence and easternmost Nova Scotia southwest to the Catskill Mountains of New York. The species inhabits an even more restricted overwintering range, occurring regularly on only four islands in the Greater Antilles. Habitat loss and degradation at both ends of its migratory spectrum suggest a tenuous conservation status for Bicknell’s Thrush, which is ranked as the Nearctic-Neotropical migrant of highest conservation priority in the Northeast (Rosenberg and Wells 1995, Pashley et al. 2000).

Following its discovery in 1881 by Eugene Bicknell on Slide Mountain in New York’s Catskill range, Robert Ridgway named and described Bicknell’s Thrush in 1882, then classifying it as a subspecies of Gray-cheeked Thrush (Catharus minimus). George Wallace’s (1939) classic natural-history study focused attention on Bicknell’s Thrush, and a careful taxonomic assessment by Henri Ouellet (1993) led to specific recognition in 1995 (Am. Ornithol. Union 1995). Although reliable field identification of Bicknell’s and Gray-cheeked thrushes remains dubious at best, marked morphological, vocal, and biochemical differences between the two taxa support this designation (Frey et al. 2008). The ranges are completely allopatric, with Gray-cheeked Thrush breeding farther north (Newfoundland to Siberia) and wintering farther south (Panama through northwestern Brazil and Colombia) than Bicknell’s Thrush.

Bicknell’s Thrush is adapted to naturally disturbed habitats. Historically, the species probably selected patches of regenerating forest caused by fir waves, wind throw, ice and snow damage, fire, and insect outbreaks, as well as chronically disturbed, stunted altitudinal and coastal conifer forests (Ouellet 1993, Nixon 1999). In addition to these natural successional habitats, Bicknell’s Thrush has recently been discovered in areas disturbed by timber harvesting, ski trail and road construction, and other human activities (Ouellet 1993). Evidence of local declines and extinctions in “traditional” breeding habitats may indicate either a shift in habitat use or increasing populations (Ouellet 1993, 1996), but more likely reflects the species’ opportunistic use of disturbed habitats.

The high-elevation spruce-fir forests that Bicknell’s Thrush rely on for breeding habitat in the United States may be threatened by the effects of climate change (Rodenhouse et al. 2008) and atmospheric deposition of pollutants such as mercury (Rimmer et al. 2005, Townsend et al. 2013). Extensive loss and degradation of the tropical broadleaf forests that Bicknell’s Thrush prefer in winter, particularly mid-elevation rainforest habitat, pose the greatest threat to the species’ long-term viability (Rimmer et al. 2005, 2010, Townsend et al. 2012). Ongoing conservation efforts are focused on preserving remaining blocks of wet forest habitat in the Caribbean (Townsend et al. 2012, McFarland et al. 2013) and using novel conservation tools, such as payment for ecosystem services, to balance the needs of human economic development with the ecosystem services provided by intact forest habitat (Kerchner et al. 2010).