Bicknell's Thrush


Nearly half a century has passed since the gyrating song and piercing nasal calls of Bicknell’s Thrush rang from the summit of Mount Greylock in northwestern Massachusetts. The disappearance of the species from this peak, its only known haunt in the state, was well documented by birders during the 1900s and provided one of the earliest warning signals that all might not be well.

Over twenty years ago, we rang a cautionary alarm for Bicknell’s Thrush, at that time a recognized subspecies of Gray-cheeked Thrush (C. minimus) and one of eastern North America’s most rare and poorly known songbirds. Now known as a distinct species and one of the region’s highest conservation priority migratory songbirds, Bicknell’s Thrush has been the subject of much intensive study. Yet, it remains as rare and vulnerable as ever, likely more so.

This enigmatic songbird has not yielded its secrets easily. Occupying windswept mountaintop conifer forests in summer and dense broadleaf cloud forests in winter, Bicknell’s Thrush has kept biologists at bay. However, a determined cadre of scientists and conservationists, combining “brute force biology” with technology and resourcefulness, has made remarkable inroads during the past two decades into understanding this bird.

Twenty years after our initial foray into the realm of Bicknell’s Thrush, one conclusion is clear: we humans have stacked the deck decidedly against this globally rare and vulnerable species. We’ve fragmented its mountaintop breeding haunts with ski areas, towers, and turbines. Our warming climate threatens to push the Northeast’s montane fir forests to extinction, with predicted losses of >90% with as little as a 2 C rise in summer temperatures. We’ve discovered surprisingly high burdens of toxic mercury in the blood and feathers of every thrush sampled from Canada to the Catskills, from Cuba to Hispaniola. We’re watching its limited winter habitats disappear before our eyes. Thanks largely to a legion of Mountain Birdwatch volunteers, we’re able to monitor populations across its breeding range to follow how populations are doing. In New England and New York, regional trends appear mixed, with evidence of declines in core areas like the White Mountains, but no clear increases or decreases in others. Maritime Canadian populations, however, are in free fall, with sharp annual declines of 11.5% in New Brunswick and 7.4% in Nova Scotia . Quebec trends are less certain, but also indicate declines. Continued monitoring across the breeding range is a high priority, and Mountain Birdwatch volunteers are always needed.


Concerted actions are now underway to conserve Bicknell’s Thrush—actions we hope will reverse disturbing trends that have led to the recently proposed listing for this at-risk species under the U.S. Endangered and Threatened Species Act. A coalition of scientists, natural resource managers, and conservationists from across the hemisphere are now translating knowledge into action. The International Bicknell’s Thrush Conservation Group (IBTCG) formed in 2007 with an explicit aim to advance conservation of the species. Nearly one hundred members strong, the IBTCG released in 2010 a detailed and formal action plan, with an ambitious goal “to increase the global population of Bicknell’s Thrush by 25% over the next fifty years (2011-2060), with no further net loss of distribution”. Recommended actions concentrate on range-wide research, monitoring, and habitat conservation. Importantly, the plan directs foremost attention to better protection of its dwindling winter habitats.


Townsend, J.T., C.T. Driscoll, C.C. Rimmer, and K.P. McFarland. 2014. Avian, salamander, and forest floor mercury concentrations increase with elevation in a terrestrial ecosystem. Environmental Toxicology and Chemistry 33:208-215.

Townsend, J.M., C.C. Rimmer, C.T. Driscoll, K.P. McFarland, and E.E. Iñigo-Elias. 2013. Mercury concentrations in tropical resident and migrant songbirds on Hispaniola. Ecotoxicology Volume 22 (1): 86-93. DOI 10.1007/s10646-012-1005-1. (Abstract)

McFarland, K.P., C.C. Rimmer, J.E. Goetz, Y. Aubry, J.M. Wunderle Jr., A. Sutton, J.M. Townsend, A. Llanes Sosa, and A. Kirkconnell. 2013. A Winter Distribution Model for Bicknell’s Thrush (Catharus bicknelli), a conservation tool for a threatened migratory songbird. PLOS ONE 8(1): e53986. doi:10.1371/journal.pone.0053986. (Abstract)

Townsend, J.M., C.C. Rimmer, K.P. McFarland, and J.E. Goetz. 2012. Site-specific variation in food resources, sex ratios and body condition of an overwintering migrant songbird. Auk 129: 683-690.

Townsend, J.M., C.C. Rimmer, and K.P. McFarland. 2012. Radio-transmitters do not affect seasonal mass change or annual survival of wintering Bicknell’s Thrushes. Journal of Field Ornithology 83:295-301.

Studds, C. E., McFarland, K. P., Aubry, Y., Rimmer, C. C., Hobson, K. A., Marra, P. P. and Wassenaar, L. I. 2012. Stable-hydrogen isotope measures of natal dispersal reflect observed population declines in a threatened migratory songbird. Diversity and Distributions 18: 919–930. doi: 10.1111/j.1472-4642.2012.00931.x

Townsend, J.M., C.C. Rimmer, A.T. Townsend, and K.P. McFarland. 2011. Sex and age ratios of Bicknell’s Thrush wintering in Hispaniola. Wilson Journal of Ornithology 123:367-372.

Frey, S. J. K., A. M. Strong, and K. P. McFarland. 2011. The relative contribution of local habitat and landscape context to metapopulation processes: a dynamic occupancy modeling approach. Ecography 34:001-009.

Rimmer, C.C., J.E. Goetz, E. Garrido Gomez, J.L. Brocca, P. Bayard, and J.V. Hilaire. 2010. Avifaunal surveys in La Visite National Park–last vestiges of montane broadleaf forest in eastern Haiti. Journal of Caribbean Ornithology 23:31-43.

Townsend, J.M, C.C. Rimmer, and K.P. McFarland. 2010. Winter territoriality and spatial behavior of Bicknell’s Thrush (Catharus bicknelli) at two ecologically distinct sites in the Dominican Republic. Auk 127:514-522.

Kerchner, C., M. Homzak, R. Kemkes, A. Richardson, J.M. Townsend, and C.C. Rimmer. 2010. Designing spatially explicit incentive programs for habitat conservation: a case study of the Bicknell’s Thrush winter grounds. Ecological Economics 69:2018-2015.

Rimmer, C.C., E.K. Miller, K.P. McFarland, R.J. Taylor, and S.D. Faccio. 2009. Mercury bioaccumulation and trophic transfer in the terrestrial food web of a montane forest. Ecotoxicology. DOI 10.1007s10646-009-0443-x.

Townsend, J.M., C.C. Rimmer, and K.P. McFarland. 2009. Investigating the limiting factors of a rare, vulnerable species: Bicknell’s Thrush. Proceedings of the Fourth International Partners in Flight Conference: Tundra to Tropics: 91-95.

Townsend, J.M., C.C. Rimmer, J. Brocca, K.P. McFarland, and A. K. Townsend. 2009. Predation of a wintering migratory songbird by introduced rats: can nocturnal roosting behavior serve as predator avoidance? Condor 111(3): 565-569.

Lambert, J.D., D.I. King, J.P. Buonaccorsi and L.S. Prout. 2008. Decline of a New Hampshire Bicknell’s Thrush Population, 1993-2003. Northeastern Naturalist 15: 607-618.

Frey, S.J.K., C.C. Rimmer, K.P. McFarland, and S. Menu. 2008. Identification and sex determination of Bicknell’s Thrushes using Morphometric Data. J. of Field Ornithology 79: 408-420.

Rodenhouse, N.L., S.N. Matthews, K.P. McFarland, J.D. Lambert, L.R. Iverson, A. Prasad, T.S. Sillett, and R.T. Holmes. 2008. Potential effects of climate change on birds of the Northeast. Mitigation and Adaptation Strategies for Global Change 13: 517-540.

Townsend, J.M. and C.C. Rimmer. 2006. Known natal and wintering sites of a Bicknell’s Thrush. Journal of Field Ornithology 77: 452-454.

Christopher C. Rimmer, Jason M. Townsend, Andrea K. Townsend, Eladio M. Fernández, & Jesus Almonte. 2005. Avian diversity, abundance, and conservation status in the Macaya Biosphere Reserve of Haiti. Ornitologia Neotropical 16: 219–230.

Lambert, J. D., K. P. McFarland, C. C. Rimmer, S. D. Faccio, and J. L. Atwood. 2005. A practical model of Bicknell’s Thrush distribution in the northeastern United States. Wilson Bulletin 117:1-11.

Rimmer, C.C. 2005. Bird conservation in Haiti: it’s now or never to save Haiti’s birds. Journal of Caribbean Ornithology 18:86-87.

Rimmer, C.C., K. P. McFarland, D. C. Evers, E. K. Miller, Y. Aubry, D. Busby, and R. J. Taylor. 2005. Mercury levels in Bicknell’s thrush and other insectivorous passerine birds in montane forests of the northeastern United States and Canada. Ecotoxicology 14:223-240.

Strong, A.M., C.C. Rimmer, and K.P. McFarland. 2004. Effect of prey biomass on reproductive success and mating strategy of Bicknell’s Thrush (Catharus bicknelli), a polygynandrous songbird. Auk 121:446-451.

Goetz, J.E.., K. P. McFarland and C.C. Rimmer. 2003. Multiple paternity and multiple male feeders in Bicknell’s Thrush (Catharus bicknelli). Auk 120: 1044-1053.

Strong, A. M., C. C. Rimmer, K.P. McFarland and K. Hagan. 2002. Effects of mountain resorts on wildlife. Vermont Law Review 26(3): 689-716.

Rimmer, C.C. and K.P. McFarland. 2001. Known breeding and wintering sites of Bicknell’s Thrush. Wilson Bull.113: 234-236.

Rimmer, C.C., K.P. McFarland, W.G. Ellison, J.E. Goetz and H. Ouellet. 2001. Bicknell’s Thrush (Catharus bicknelli). In The Birds of North America, (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, and The American Ornithologists’ Union, Washington, D.C.

Hobson, K.A., K.P. McFarland, L.I. Wassenaar, C.C. Rimmer and J.E. Goetz. 2001. Linking breeding and wintering grounds of Bicknell’s Thrushes using stable isotope analyses of feathers. Auk 118:16-23.

McFarland, K.P. and C.C. Rimmer. 1996. Horsehair fungus (Marasmius androsaceus) used as nest lining by the Bicknell’s Thrush (Catharus bicknelli) and other subalpine spruce-fir forest bird species. Canadian Field-Naturalist 110: 541-544.

Rimmer, C.C., J.L. Atwood, K.P. McFarland, and L.R. Nagy. 1995. Population density, vocal behavior and recommended survey methods for Bicknell’s Thrush. Wilson Bull. 108:639-649.

Atwood, J.L., C.C. Rimmer, K.P. McFarland, S.H. Tsai, and L.R. Nagy. 1995. Distribution of Bicknell’s Thrush in New England and New York. Wilson Bull. 108: 650-661.