New York Natural Heritage Program
Bicknell's Thrush
Catharus bicknelli (Ridgway, 1882)
Birds

Habitat [-]
This species is a habitat specialist restricted to naturally, and human-disturbed, montane spruce/fir forests with lesser amounts of other hardwoods such as Mountain Ash and Yellow Birch above about 3000 ft. Since there is a strong negative correlation between latitude and temperature, spruce/fir caps mountain tops at comparatively higher elevations in the Catskills than in the Adirondacks. Therefore, thrushes will nest down to about 2700 ft. in the Adirondacks, but generally only above 3500 ft. in the Catskills (Lambert et al. 2005). The highest nest densities are often associated with stunted Balsam fir areas along exposed ridgelines chronically disturbed by high winds and ice accumulation (Rimmer et al. 2001). There is some uncertainty about the importance of Bicknell's use of habitat ecotones at the lower elevational limits of occupancy (Hale 2006) and interspecific interactions with congeners, especially Swainson's Thrushes (Able and Noon 1976) at lower elevations. As the climate in the northeast warms, the spruce/fir ecotone presumably will migrate upslope (Rodenhouse et al. 2007), possibly favoring Swainson's, since Bicknell's is physiologically adapted to cooler temperatures (Holmes and Sawyer 1975). Such ecotones are well correlated with growing season temperatures; but in both the Catskills and Adirondacks only winter temperatures, not summer temperatures, have significantly risen since 1900 (Jenkins and Keal 2004). Further north in Canada, the species breeds in a wider array of habitats including low elevation coastal evergreen stands with similar forest structure to higher elevation sites, as well as dense second-growth forests (with a significant hardwood component) following large-scale disturbances such as clearcutting and/or fires (Nixon et al. 2001; Connolly et al. 2002; Campbell and Whittam 2006).

Associated Ecological Communities [-]
  • Alpine krummholz
    A dwarf woodland dominated by balsam fir that occurs at or near the summits of the high peaks of the Adirondacks.
  • Mountain fir forest
    A conifer forest that occurs at high elevations in the Catskill and Adirondack mountains, usually at elevations ranging from 3500 to 4500 ft. This forest typically occurs on cool upper slopes that are exposed to wind, at elevations above spruce-northern hardwood forests, usually above mountain spruce fir forest, and below alpine krummholz. The vegetation typically has a low species diversity; the tree layer is almost entirely balsam fir.
  • Mountain spruce-fir forest
    A conifer forest that occurs at high elevations in the Catskill and Adirondack mountains, usually at elevations ranging from 3000 to 4000 ft. This forest occurs on upper slopes that are somewhat protected from the prevailing westerly winds, usually at elevations above spruce-northern hardwood forests, and below mountain fir forests. The dominant trees are red spruce and balsam fir.
  • Spruce-fir rocky summit
    A community that occurs on cool, dry, rocky ridgetops and summits where the bedrock is non-calcareous (such as anorthosite, quartzite, or sandstone), and the soils are more or less acidic. The vegetation may be sparse or patchy, with numerous rock outcrops and rock slides. The species have predominantly boreal distributions.

Associated Species [-]
  • Swainson's Thrush (Catharus ustulatus)
  • Yellow-Rumped Warbler (Dendroica coronata)
  • Blackpoll Warbler (Dendroica striata)
  • Dark-Eyed Junco (Junco hyemalis)
  • Winter Wren (Troglodytes troglodytes)
  • White-Throated Sparrow (Zonotrichia albicollis)