Relative abundance and range extensions of bird species in central Labrador

Abstract

Bird communities in Labrador remain poorly described, including in the lower Churchill River valley, which lies within an offshoot of the boreal shield ecozone and features vegetation communities typically found more than 100 km to the south. Between 2006 and 2016, we conducted 1139 point counts in June and early July at 617 sites along 63 routes within and adjacent to the lower Churchill River valley. We documented 80 species during the surveys and a further nine species incidentally. The most numerous species were Swainson’s Thrush (Catharus ustulatus), Ruby-crowned Kinglet (Corthylio calendula), and Dark-eyed Junco (Junco hyemalis). Relative bird abundance was highest in hardwood and mixedwood forests and lowest in areas dominated by Black Spruce (Picea mariana). Among the species we observed were 19 that we considered to be regionally rare, based on existing documentation. The most abundant of these were Least Flycatcher (Empidonax minimus), Cedar Waxwing (Bombycilla cedrorum), and Magnolia Warbler (Setophaga magnolia), each with more than 80 observations over multiple years, spanning 10 or more areas within the lower Churchill River valley. Almost all of the regionally rare species were strongly associated with either hardwood forests, large conifers, or dense riparian vegetation. These features are relatively widespread within the lower Churchill River valley, but scarce elsewhere in Labrador. It is unclear whether the results observed represent recent range expansions or our surveys were simply the first to document long-standing regional populations; regardless, we recommend that our records be considered in future revisions to range maps for these species.