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Technical Thematic Report No. 12. - Landbird trends in Canada, 1968-2006

Boreal Cordillera Ecozone+ (southern portion of BCR 4)

Contributor: Pam Sinclair

Much of the Boreal Cordillera area is remote wilderness, inaccessible by road. BBScoverage in the Boreal Cordillera is concentrated in the southwestern portion of the Yukon and along the northern border of British Columbia. The results presented are based on data from 1988 to 2006 because earlier years had too few BBS routes. Results have low precision and a short-time frame (19 years) relative to other ecozones+.

The Boreal Cordillera is largely forested; therefore, landbird species selected as representative of this ecozone+belong mainly to the forest and shrub/early successional assemblages. Urban/suburban, other open habitat, and grassland assemblages are not reported here because they are a very minor part of the avifauna, with few species and poor BBS trend precision.

Table 54. Trends in abundance of landbirds for the Boreal Cordillera Ecozone+, based on data from the Breeding Bird Survey. The following table shows the BBS Abundance Index by decade from the 1980s to the 2000s.Footnote1
Species AssemblageTrend
(%/yr)
P1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Forest Birds1.6% 162.3161.8175.08%
Shrub / Successional0.6% 35.129.631.7-10%

Table 54 - Footnotes

Footnote 1

In this table: P is the statistical significance; 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 (1980s) and the 2000s (2000-2006).

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The overall trend in forest landbirds as a group has been slightly positive, while the shrub/successional assemblage has been relatively stable over the last two decades (Table 54). There is considerable year-to-year variation in these assemblages because bird populations fluctuate in response to a variety of factors including climatic variation and food availability. One factor that likely influences landbird trends in the Pacific northwest is the Pacific Decadal Oscillation (Hare and Mantua, 2000) which is a pattern of surface temperature variability in the Pacific Ocean that results in alternating "warm" and "cool" climatic phases in the northeastern Pacific which last for two to three decades although there can be temperature variation within the phases.

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Forest bird assemblage

The overall trend for the forest bird assemblage is slightly positive (Table 54 and Figure 44) though not statistically distinguishable from a stable trend. Trends for most of the individual species presented have also been stable or positive (Table 55). The trend for Western Wood-pewee has been relatively stable in the Boreal Cordillera and stable, tending positive overall in Canada. However, it has declined in some other ecozones+, particularly in the Pacific Maritime, and has shown a significant decline in North America as a whole (Sauer et al., 2008). The Common Raven, a widespread species that is tolerant of and often benefits from human-influenced landscapes, is increasing in the Boreal Cordillera and across its range in Canada. Raven populations decreased during the early part of the 20th century in the east and Prairies, but have since increased and are spreading back into their previous range. Suggested causes for the early decrease in these regions include control measures, land use changes, and competition from increases in American Crow (Boarman and Heinrich, 1999). Boreal Chickadees have a positive population trend here and in the Boreal Plains, in contrast to statistically significant declines in the Boreal Shield, Montane Cordillera, Atlantic Maritime, and at the national level.

Figure 44. Annual indices of population change in birds of forest habitat for the Boreal Cordillera Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 44

This line graph shows annual indices of population change in birds of forest habitat for the Boreal Cordillera Ecozone+, based on data from the Breeding Bird Survey from 1988 to 2006. The abundance index shows a slightly positive trend, with a range between approximately 110 and 220.

 

Table 55. Trends in abundance of forest birds for the Boreal Cordillera Ecozone+, based on data from the Breeding Bird Survey. The following table shows the BBS Abundance Index by decade from the 1980s to the 2000s.Footnote1
Forest BirdsPopulation
Trend (%/yr)
P1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Western Wood-Pewee-0.10% 2.12.92.414%
Northern Flicker0.00% 1.52.92.350%
Dark-eyed Junco0.50% 44.140.043.8-1%
Swainson's Thrush1.92% 40.643.047.216%
Common Raven2.02% 2.13.73.466%
Gray Jay2.43% 7.89.310.534%
Yellow-rumped Warbler3.36%n20.331.234.268%
Boreal Chickadee3.87% 1.71.82.021%

Table 55 - Footnotes

Footnote 1

In this table: 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 (1980s) and the 2000s (2000-2006). Species are listed in order from those showing most severe declines to those showing the most positive increases

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Shrub/early successional bird assemblage

The shrub/early successional assemblage has been relatively stable overall with a mix of increases and decreases in individual species (Figure 45 and Table 56). Widespread species such as Lincoln’s Sparrow and Yellow Warbler have shown increasing and stable trends respectively, consistent with their national trends. Lincoln’s Sparrow trends have been stable or increasing in all ecozones+; however, maintenance of wide road verges in the north may benefit this species locally and they may be over-represented in BBScounts (C. Machtans, Environment Canada, pers. comm., 2010). Trends for Yellow Warbler vary across Canada but have been more negative in the western ecozones+. Common Yellowthroat has increased in the Boreal Cordillera but has declined in Canada overall, particularly in the Boreal Shield and Boreal Plains, and in North American overall (Sauer et al.,2008).

Figure 45. Annual indices of population change in birds of shrub/early successional habitat for the Boreal Cordillera Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 45

This line graph shows annual indices of population change in birds of shrub/early successional habitat for the Boreal Cordillera Ecozone+, based on data from the Breeding Bird Survey from 1988 to 2006. The overall population trend is slightly positive, though it is not a stable a trend. The abundance index fluctuates between 35 and 23 during the period.

 

Table 56. Trends in abundance of shrub/early successional birds for the Boreal Cordillera Ecozone+, based on data from the Breeding Bird Survey. The following table shows the BBS Abundance Index by decade from the 1980s to the 2000s.Footnote1
Birds of Shrub / SuccessionPopulation
Trend (%/yr)
P1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
White-crowned Sparrow-2.86% 9.97.05.1-48%
Wilson's Warbler-1.49% 4.94.53.4-30%
Alder Flycatcher-1.29% 7.44.85.4-26%
Yellow Warbler0.00% 2.93.83.522%
Lincoln's Sparrow4.60% 1.22.42.4103%
Common Yellowthroat4.71%*1.92.12.637%

Table 56 - Footnotes

Footnote 1

In this table: P is the statistical significance; * indicates P<0.05; no value indicates not significant (P>0.1); “Change” is the percent change in the average index of abundance between the first decade for which there are results (1980s) and the 2000s (2000-2006). Species are listed in order from those showing most severe declines to those showing the most positive increases.

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