• 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: one of eastern North America’s rarest and poorly known songbirds. Now one of the region’s highest conservation priorities, Bicknell’s Thrush has been the subject of ongoing intensive study by the Vermont Center of Ecostudies and our colleagues. Yet, it remains as rare and vulnerable as ever, likely more so.

    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. Our warming climate threatens to push the Northeast’s montane spruce-fir forests to extinction, with predicted losses of >50% within the next several hundred years. We’ve fragmented its mountaintop breeding haunts with ski areas, towers, and turbines. We’ve discovered surprisingly high burdens of toxic mercury from atmospheric pollution in the blood and feathers of every thrush sampled from Canada and the Catskills to its wintering grounds in Cuba and Hispaniola. We’re watching its limited winter habitats disappear before our eyes due to illegal deforestation.


    We’re tracking Bicknell’s Thrush to their wintering grounds using light-level geolocators and working with our Canadian colleague Junior Tremblay (Research scientist – Boreal birds & Ecosystems) to track their migratory movements using nanotags and the Motus network. We’re just finished a long-term survival analysis of Bicknell’s Thrush, looking at the effects of summer weather and hurricanes and deforestation on the wintering grounds (more to come soon).

    Thanks largely to a legion of Mountain Birdwatch citizen scientists, we’re able to monitor breeding populations across the northeastern U.S. and we recently release a comprehensive State of the Mountain Birds report. Our recent research in Ecosphere, estimated only ~71,000 adult birds in the U.S., and likely <120,000 globally. We estimated that just three public lands (White Mountain National Forest [NH & ME], Baxter State Park [ME], and the High Peaks Wilderness Area (NY) harbor >50% of the U.S. Bicknell’s Thrush population. Our abundance map of Bicknell’s Thrush can be downloaded or viewed online at Data Basin. We anticipate that these findings will prove useful in generating statistically defensible estimates of the conservation status of the species, evaluating conservation actions, and identifying segments of the Bicknell’s Thrush population that occur on lands vulnerable to future development.


    Concerted on-the-ground actions are now underway to conserve Bicknell’s Thrush. A coalition of scientists, natural resource managers, and conservationists from across the hemisphere are now translating knowledge into action via the International Bicknell’s Thrush Conservation Group (IBTCG). Nearly one hundred members strong, the IBTCG released a formal action plan in 2010, 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.

    We are meeting these goals with winter habitat surveys for Bicknell’s Thrush in Cuba and Puerto Rico. In the heart of the Bicknell’s Thrush winter range, VCE is supporting the creation of a strategic conservation plan for the Sierra de Bahoruco National Park in the Dominican Republic. With funding from a US Fish and Wildlife Service Neotropical Migratory Bird Conservation Act grant, we are hosting workshops with community members and farmers, government officials and scientists. These meetings are organized in collaboration with our local partner, Grupo Jaragua, and the Dominican Republic’s Ministry of the Environment and Natural Resources.


    Hill, J. M., J. D. Lloyd, K. P. McFarland, and C. C. Rimmer. 2019. Apparent survival of a range-restricted montane forest bird species is influenced by weather throughout the annual cycle. Avian Conservation and Ecology 14(2):16.

    Hill, J.M., and J.D. Lloyd. 2017. A fine-scale U.S. population estimate of a montane spruce-fir bird species of conservation concern. Ecosphere 8: e01921. DOI: 10.1002/ecs2.1921.

    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. DOI: 10.1002/etc.2438

    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 22(1): 86-93. DOI 10.1007/s10646-012-1005-1. DOI: 10.1007/s10646-012-1005-1

    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 (<i>Catharus bicknelli</i>), a conservation tool for a threatened migratory songbird. PLOS ONE 8(1): e53986. DOI:10.1371/journal.pone.0053986.

    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. DOI: 10.1525/auk.2012.12043

    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. DOI: 10.1111/j.1557-9263.2012.00378.x

    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. DOI: 10.1676/10-065.1

    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. DOI: 10.1111/j.1600-0587.2011.06936.x

    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 (<i>Catharus bicknelli</i>) at two ecologically distinct sites in the Dominican Republic. Auk 127:514-522. DOI: 10.1525/auk.2010.09160

    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. DOI: 10.1016/j.ecolecon.2009.08.031

    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. DOI: 10.1525/cond.2009.090062

    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. DOI: 10.1656/1092-6194-15.4.607

    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. DOI: 10.1111/j.1557-9263.2008.00192.x

    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. DOI: 10.1007/s11027-007-9126-1

    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. DOI: 10.1676/04-013

    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. DOI: 10.1007/s10646-004-6270-1

    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.