Technical Thematic Report No. 12. - Landbird trends in Canada, 1968-2006
The Arctic Ecozone+ is relatively isolated and pristine and there are few immediate threats to landbirds from human activity, although species are affected by climate change, contaminants, and other wide-ranging factors. All birds listed here overwinter in more populated areas of Canada and the United States; development pressures are more intense both in their wintering ranges and along their migration routes. Canada has a high stewardship responsibility for these species because large portions of their western hemisphere breeding populations are concentrated in the Arctic Ecozone+.
There are relatively few landbird species in the Arctic Ecozone+ and few data on their population trends. Addressing the lack of information on population status and trends has been highlighted as the most pressing conservation need in relation to landbirds for this region (Rich et al., 2004). Because of remoteness and lack of roads, the BBS has not been carried and there are few other surveys of breeding birds. However, since many birds that breed in the Arctic spend their winters in the United States and more southerly parts of Canada, CBC data are available for some species. Results presented below are preliminary findings based on CBC data from Canada and the United States combined (Butcher and Niven, 2007).
CBC trends (Table 58 and Figure 48) indicate that several species, such as Harris’s Sparrow and Snowy Owl, have been undergoing long-term, statistically significant declines since the 1960s. Other species, such as Rough-legged Hawk and Lapland Longspur, have shown relatively stable overall population trends.
|American Tree Sparrow||-2.16%||*||62.8||56.3||42.4||34.4||-45%|
Table 58 - Footnotes
- Footnote 1
Table shows the annual rate of change and the average CBC abundance index by decade; Asterisks (*) indicate significant trends (P<0.05); P is the statistical significance: * indicates P<0.05; n indicates 0.05<P<0.1; no value indicates not significant; “Change” is the percent change in the average index of abundance between the first decade for which there are results (1970s) and the 2000s (2000-2006).
Source: based on data from the Christmas Bird Count by Butcher and Niven (2007)
Figure 48. 1966 to 2005, based on Christmas Bird Count results for North America.
Long Description for Figure 48
This graphic presents four line graphs showing the annual indices of population change for the Rough-legged Hawk, Snowy Owl, Harris’s Sparrow, and Snow Bunting, 1966 to 2005, based on Christmas Bird Count results for North America. The graphs are described in the following points:
- Rough-legged Hawk: The abundance index shows relatively stable populations through the period, fluctuating between 1.5 and 2.0.
- Harris’s Sparrow: The abundance index shows a long-term significant trend, declining from approximately 12 to 5 over the period.
- Snowy Owl: The abundance index shows a long-term significant trend declining from almost 0.5 to 0.1 over the period.
- Snow Bunting: The abundance index shows relatively stable populations through the period, fluctuating between 22 and 6 over the period.
The Rough-legged Hawk and Snow Bunting show no significant trends, though the latter may be in decline; the Snowy Owl and Harris’s Sparrow have declined significantly (P>0.05)
Source: based on data from the Christmas Bird Count, 1966-2005 (courtesy D. Niven, Audubon).
Harris’s Sparrow, a species with its entire breeding range in Canada, is classified by Partners in Flight as a Continental Watch List species (Rich et al., 2004). The species has apparently experienced a long-term decline over the last 40 years (Figure 48). Because of its isolated breeding range, direct influence of human activity on the breeding range is unlikely to be a factor in its decline. Harris’s Sparrows, however, are susceptible to predation, especially by Merlins, whose populations are increasing. The influence of factors such as climate change is unknown (Niven et al., 2004; Norment and Shackleton, 2008).
Population indices for Snow Bunting vary annually but this species has apparently experienced a large decline in its population over the long term (Figure 48). The Arctic has a very high stewardship responsibility for Snow Buntings (Rich et al., 2004), which breed throughout the Arctic Cordillera and Northern Arctic and the northern portions of the Southern Arctic. Reduction in Snow Bunting populations may be related to earlier thawing of the tundra and conversion of open sites, its preferred nesting habitat, to more shrub-dominated communities. In addition, climate warming allows more avian and mammalian predators to survive and prey on Snow Bunting nests (Audubon Society, 2007).
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