VU
Bicknell's Thrush Catharus bicknelli



Justification

Justification of Red List Category
This species is listed as Vulnerable because its population is suspected to be in rapid decline overall, on the basis of regional trend data and knowledge of on-going threats.

Population justification
Hill and Lloyd (2017) estimate there to be 71,318 individuals (c. 56,080-89,748) in the U.S.A. whilst COSEWIC (2009) suggested a population of 40,570 and 49,258 individuals in Canada. This suggests a population size between 111,888 and 120,396 individuals, similar to the overall population sizes suggested by IBTCG (2010), 95,000-126,000 individuals and Hill and Lloyd (2017), <120,000 individuals. The population is therefore assumed to comprise fewer than 120,000 individuals, or 80,000 mature individuals.

Trend justification
Breeding population trend data for the species are sparse, but generally indicate declines, especially in core and northern parts of the range. The State of the Mountains Birds Report (2020) suggests an annual decline of ~2.41% per year throughout the USA (c. 60% of the species's population), which equates to a decline of ~21.6% over a ten year period (Hill 2020). Much more rapid declines have however, been noted throughout parts of the species's breeding range in recent years with rates of 7-19% noted (IBTCG 2010), including declines of 16% and 11% per year in New Brunswick and Nova Scotia, Canada respectively between 2002 and 2010 (Campbell 2011). Therefore, as declines appear to be rapid and those in Canada may well outweigh those of the USA, the species is precautionarily assumed to be declining at a rate in excess of 30% per decade, placed here in the range, 30-49%.

Distribution and population

Catharus bicknelli breeds patchily in south-east Quebec and the Maritime provinces, Canada, and eastern New York and northern New England, U.S.A. (Phillips 1991; Ouellet 1993; Atwood et al. 1996). There are an estimated 71,318 individuals in the USA  (Hill and Lloyd 2017) and 1,000-3,000 birds in the Maritime provinces (D. Busby in litt. 1999), but there have been local extinctions (C. C. Rimmer in litt. 1998, 1999). It migrates along the coast to winter in the Caribbean (Raffaele et al. 1998). The stronghold is the Dominican Republic (especially the Sierra de Baoruco and Cordillera Central) whilst it also occurs in HaitiPuerto Rico (almost entirely within the high elevations in the Cordillera Central [Rimmer et al. 2019]), eastern Cuba and in the Blue Mountains of Jamaica (McFarland et al. 2013; Lloyd and Rimmer 2017; Rimmer et al. 2019; eBird 2020). The population is suspected to be in rapid decline overall. Population trend data show mixed results, but annual declines of 7-19% have been documented in parts of the species’s breeding range (IBTCG 2010). An analysis of several combined data sets revealed an overall decline of c.2.5% per year in New York and New England (Ralston et al. 2015). Surveys (conducted through the High Elevation Landbird Program) in New Brunswick and Nova Scotia recorded apparent declines of c.16% per year and 11% per year respectively between 2002 and 2010 (Campbell 2011). Results from the second Maritime Breeding Bird Atlas show a greater than 40% decline in the distribution of the species between 1999 and 2009 (COSEWIC 2009). The State of the Mountain Birds 2020 report (Vermont Centre for Ecostudies) suggests such declines exhibit strong regional and temporal variability however, it concurrently concludes that the species has likely declined by ~2.41% per year over the last decade throughout the USA, despite localised increases (e.g. Vermont), and that populations are likely declining globally (Hill 2020). The current population estimate for the species in Canada is between 40,570 and 49,258 birds (COSEWIC 2009), with global estimates of <120,000 individuals (IBTCG 2010; Hill and Lloyd 2017). 

Ecology

In the United States, it breeds in dense montane forests (generally above 900 m), dominated by balsam fir Abies balsamae with red spruce Picea rubens and heart-leaved paper birch (Atwood et al. 1996; Rimmer 1996). In Canada, it also inhabits regenerating clear-cuts and coastal areas with spruce-fir at low elevations (Atwood et al. 1996). In winter, it occurs in moist broadleaved and mixed pine-broadleaved montane forests and secondary woodlands (Rimmer 1996; Raffaele et al. 1998; Rimmer et al. 1999; Townsend et al. 2011, 2012). It nests in June-July (present on breeding grounds May-October), sometimes with high failure rates (Rimmer 1996). The species sexually segregates in winter with females typically occurring in moderately disturbed mid-elevation rainforests of the Cordillera Septentrional and males more commonly found in the more prisitine cloud forest of remote ranges such as Sierra de Bahoruco and Cordillera Central in the Dominican Republic (McFarland et al. 2018).

Threats

The species is impacted by a number of threats however, the three most significant primary threats are currently considered to be: incompatible forestry practices throughout breeding grounds, particularly in Canada; the clearing and burning of forests in wintering habitat in the Dominican Republic and Haiti for conversion to agricultural fields and additional land uses; and ongoing climate change and a shift and contraction of its breeding range (Lloyd and McFarland 2017). In Quebec, the widespread practice of thinning renders habitat unsuitable (G. Seutin in litt. 1999) and forest loss within this species's range is currently estimated at ~2.78% across a ten year period (Tracewski et al. 2016). Agricultural conversion, logging, mining and charcoal production are rapidly clearing and fragmenting winter habitat (Atwood et al. 1996; C. C. Rimmer in litt. 1998, 1999; Lloyd and McFarland 2017) whilst invasive rats Rattus rattus  pose a threat through predation in the winter range (Erickson 2011). Furthermore, projected climate change is expected to result in dramatic decreases in the extent of suitable habitat in the species's breeding habitat, predominantly through the replacement of balsam fir by unsuitable hardwood forest (C. C. Rimmer in litt. 1998, 1999; K. McFarland in litt. 1999; Rodenhouse et al. 2008; Ralston and Kirchman 2013; Lloyd and McFarland 2017); climate change is currently predicted to reduce suitable montane balsam fir forest within its breeding habitat by over 50% by 2100 under worst-case climate change scenarios, with severe effects evident by just 2080 (Hill and Lloyd 2017; Cadieux et al. 2019). Furthermore, whilst warmer temperatures are expected to force this species upslope on mountains that lack the elevation extent to accommodate such change, asymmetrical interspecific aggression from the Swainson's Thrush (Catharus ustulatus) migrating up from below may further 'push' Bicknell's Thrush upslope, restricting its range and increasing its threat to a greater extent (Freeman and Montgomery 2016). Acid precipitation may have damaged breeding habitat in the 1960s and 1970s (Phillips 1991; Rimmer 1996) although it is thought to have predominantly impacted one tree species that is not widely abundant throughout this species's montane forest habitat (K. McFarland in litt. 2020). Ski-resort, communication and wind-power developments potentially threaten local populations (Atwood et al. 1996; Rimmer 1996). The species has been seen to be most seriously adversely impacted during the construction and early operational years of wind infrastructure due to habitat loss and disturbance, however many site were recolonised within 8 years post-construction (Lemaître and Lamarre 2020).

Conservation actions

Conservation Actions Underway
CMS Appendix II. SPAW Protocol Annex II. There is much research activity in the breeding range and, increasingly, the Caribbean. Some important breeding areas and c.50% of sites in the Dominican Republic are actively protected (Rimmer et al. 1999), but recent funding requests for management were turned down. Management and protection of existing reserves and parks is now inadequate (C. Rimmer in litt. 2003) although almost one-third of available wintering habitat remains within protected areas (McFarland et al. 2013). A 400 ha abandoned farm, situated along the Cordillera Septentrional between existing protected areas in the Dominican Republic, was recently purchased through the application of a Bicknell's Thrush abundance model and in doing so, became the Dominican Republic's first-ever private reserve, targeted at the conservation of this species (McFarland et al. 2018). A predictive model has recently been developed to produce a fine-scale population estimate for the species throughout the USA (Hill and Lloyd 2017); modelled distributions and population sizes should be used to inform and plan habitat management/alteration decisions (Lambert et al. 2005). New (and expansion of existing) ski-resorts are developed following environmental impact assessment, in a way that mitigates against habitat loss and disturbance (Anon. 2006). One development established a fund for protecting the wintering grounds (Anon. 2006). A conservation action plan was produced for the species in 2010 by the International Bicknell’s Thrush Conservation Group (IBTCG), with the overall goal of achieving a 25% population increase during the period 2011-2060 and no further net loss in distribution (IBTCG 2010). This action plan was updated in 2017 to provide contemporary, up-to-date assessments of the species status and threats, and conservation actions required for its preservation (Lloyd and McFarland 2017).

Conservation Actions Proposed
Further clarify distribution and migration details (Atwood et al. 1996; Rimmer 1996). Evaluate human impacts on breeding birds (C. C. Rimmer in litt. 1998, 1999). Further clarify winter segregation (C. C. Rimmer in litt. 1998, 1999). Develop strategies to maintain dense stands of regenerating balsam fir in Quebec. Develop management plans for existing, and designate new, reserves in the Dominican Republic (C. C. Rimmer in litt. 1998, 1999; Rimmer et al. 1999). Other actions listed by the IBTCG 2017 action plan include: protection of wintering habitat and control of invasive mammals in such habitat, implementation of best-use forestry practices throughout the breeding range and strengthening enforcement of protected area boundaries to prevent further deforestation, and climate change mitigation efforts (Lloyd and McFarland 2017).

Identification

16-19 cm. Small thrush. Buffy-brown upperparts. Bold black spotting on sides of throat and creamy-buff breast. Rest of underparts white. Greyish cheeks and lores, and dark reddish-brown tail. Similar spp. Smaller than Grey-cheeked Thrush C. minimus, and browner above with paler lores, buffier on breast and has yellow (not pink) on lower mandible. Swainson's Thrush C. ustulatus shows distinct eye-ring. Veery C. fuscescens is redder above and more finely spotted below. Hermit Thrush C. guttatus shows rufous tail. Voice Song, high-pitched chook-chook wee-o wee-o wee-o-tee-t-ter-ee descending at end. Call, harsh slurred whistle. Hints Best located by song in breeding areas.

Acknowledgements

Text account compilers
Wheatley, H., Everest, J.

Contributors
Benstead, P., Bird, J., Busby, D., Campbell, G., Harding, M., Isherwood, I., McFarland, K., Pople, R., Ralston, J., Rimmer, C., Seutin, G., Taylor, J., Wege, D. & Whittam, B.


Recommended citation
BirdLife International (2021) Species factsheet: Catharus bicknelli. Downloaded from http://www.birdlife.org on 24/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 24/10/2021.