Bicknell's Thrush is a difficult bird to study and to monitor because it inhabits high elevations and often remote and inhospitable habitats of wind-blown, stunted spruce-fir forest. However, several surveys provide some information on population change. The Breeding Bird Survey (BBS) provides limited information from the high-elevation habitat of Bicknell's Thrush, but does cover some lower-elevation portions of the range (COSEWIC 2009b). Furthermore, though the survey covers about half the population in Canada, the sample size is small and the estimated trend relies heavily on the species' range-wide trend (i.e., the average trend across the BBS survey area, including in the United States) since there are relatively few observations of the species in any one region. BBS results suggest a large decrease in the Canadian population since the early 1970s. The Maritimes Breeding Bird Atlas, reports changes in occupancy between the first (1986-1990) and second (2006-2010) Atlas periods; 39% and 32% fewer atlas squares were occupied in New Brunswick and Nova Scotia, respectively, in the second Atlas as compared to the first (Campbell and Stewart 2012). The High Elevation Landbird Program (HELP) monitored Bicknell's Thrush in the Maritime Provinces from 2002 to 2012 at which time the protocols from the Mountain Birdwatch (MBW) were adopted. Results from these surveys suggest a continuing decrease in numbers of Bicknell's Thrush in Nova Scotia. The results for New Brunswick are less clear because in 2016 sampling strategy was further modified in this province (Campbell 2017), resulting in the highest numbers on record. Preliminary results from the Atlas of the Breeding Birds of Quebec 2017 suggest there were more atlas squares with breeding evidence of Bicknell's Thrush in the second atlas (2010-2014) compared to the first (1980-1989). However, this likely reflects the increased search effort for this species during the second atlas. Taken together, results from all these surveys suggest a large decrease in the Bicknell's Thrush population and the occupied range in Canada. In the United States, where there is less total area of potential Bicknell's Thrush habitat, but the species occurs at higher densities than in Canada (Scarl 2013), analyses of several data sources suggest the Bicknell's Thrush population has declined in the northeastern United States, though that trend is driven by the inclusion of high-elevation surveys (Ralston et al. 2015). Results for MBW in the United States suggest little overall change (Ralston et al. 2015). A quantitative population goal remains to be determined, but the species is considered below acceptable levels in Canada.
Additional information on: Mountain Birdwatch/High Elevation Landbird Program
Additional information on: Breeding Bird Survey (BBS) - Canadian analysis
