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

Western Interior Basin Ecozone+ (~ BCR 9)

Contributor: Wendy Easton

Trend results presented here from the BBS are based on the years 1973 to 2006 because few BBSroutes were run in the first five years of the survey. There are relatively few BBS routes in this region compared to others (13 to 20 BBS routes run per year in past decade) because this is a relatively small region. The routes are well distributed in the region, but under-represent areas of high elevation.

Four of the five bird habitat assemblages have undergone statistically significant long-term declines (Table 43). Only the birds of shrub/early successional assemblage have maintained a stable to positive population trend. Bird populations have been affected by the cumulative impacts of conversion of land to agricultural (including eradication of sagebrush), overgrazing by livestock, urban development, altered fire regimes, and invasion of non-native plants (Ritter, 2000; Partners in Flight British Columbia and Yukon, 2003). The region is home to several nationally and provincially listed species (Partners in Flight British Columbia and Yukon, 2003).

Table 43. Trends in abundance of landbirds for the Western Interior Basin Ecozone+, based on data from the Breeding Bird Survey. The following table shows the BBS Abundance Index by decade from the 1970s to the 2000s.Footnote1
Species AssemblageTrend
(%/yr)
P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Forest Birds-0.7%*215.4223.0206.8176.1-18%
Shrub / Successional0.5% 50.658.361.058.415%
Grassland-1.9%*48.641.836.027.9-43%
Open / Agricultural-1.8%*118.698.089.667.8-43%
Urban / Suburban-1.2%*151.5138.1124.5107.7-29%

Table 43 - 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 (1970s) and the 2000s (2000-2006).

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Forest bird assemblage

The forest bird assemblage in the Western Interior Basin shows an overall slight decline, especially since the mid-1990s (Figure 35). Individual species within the assemblage show a mix of increasing, decreasing, and stable population trends (Table 44). Declines of more than 50% of their populations are seen in several western-distributed species such as Dusky Flycatcher, Townsend’s Warbler, and Rufous Hummingbird. Mountain Chickadee, another western species, has experienced a long-term significant population decline. Western North America is an area of relatively high abundance for Pine Siskin yet declines of more than 50% have occurred in all three western ecozones+. Warbling Vireo populations are doing well here as in most other regions of Canada, with the exception of the Boreal Plains Ecozone+. Clark’s Nutcracker is increasing in the Western Interior Basin and overall in Canada. In addition to species listed in Table 44 that are relatively well monitored, there are other species considered a priority in the Western Interior Basin, including several owls and woodpeckers, which are provincial and/or nationally listed species at risk (for example, Flammulated Owl, Western Screech-Owl, Spotted Owl, Lewis’s Woodpecker, White-headed Woodpecker, and Williamson’s Sapsucker) (Partners in Flight British Columbia and Yukon, 2003).

Figure 35. Annual indices of population change in birds of forest habitat for the Western Interior Basin Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 35

This line graph shows annual indices of population change in birds of forest habitat for the Western Interior Basin Ecozone+, based on data from the Breeding Bird Survey from 1973 to 2006. The abundance index shows an overall slight decline, especially since the mid-1990s, ranging between approximately 270 and 150.

 

Table 44. Trends in abundance of selected species of forest birds that arecharacteristic of the Western Interior Ecozone+, based on data from theBreeding Bird Survey. The following table shows the BBS Abundance Index by decade from the 1970s to the 2000s.Footnote1
Forest BirdsPopulation
Trend (%/yr)
 P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Dusky Flycatcher-2.37%*13.110.48.55.6-57%
Pine Siskin-2.37%*25.533.125.916.2-36%
Townsend's Warbler-2.37% 4.94.94.02.4-51%
Rufous Hummingbird-2.08% 3.51.21.11.2-67%
Veery-2.08% 9.17.05.65.2-43%
Hammond's Flycatcher-1.78% 10.98.47.36.9-37%
Red Crossbill-1.59% 8.514.08.65.2-38%
Townsend's Solitaire-1.29% 2.23.72.41.7-24%
Mountain Chickadee-1.19%*9.59.67.97.4-23%
Cassin's Finch-1.09% 2.83.94.71.5-47%
Dark-eyed Junco-1.09% 16.822.317.412.6-25%
Yellow-rumped Warbler-0.70% 20.717.817.516.3-21%
Swainson's Thrush-0.50% 21.618.117.518.0-16%
Cassin's Vireo-0.40% 5.14.14.74.5-10%
Hairy Woodpecker-0.20% 0.81.21.10.7-13%
Western Wood-Pewee0.10% 7.57.06.37.96%
Red-naped Sapsucker0.30% 4.24.45.13.6-14%
Western Tanager1.11% 12.09.312.313.916%
Red-breasted Nuthatch3.05%*3.36.37.68.3149%
Warbling Vireo3.05%*7.311.014.115.7116%
Clark's Nutcracker5.23%*0.71.22.52.2>200%

Table 44 - 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 (1970s) 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

There has been little change in the overall trend for shrub/early successional birds (Figure 36). The overall pattern is similar to that seen in the Montane Cordillera, which shares some species. Results for most individual species (Table 45) are not statistically significant but show a mix of declines and increases. The western population of Nashville Warbler shows a strong increase in the Western Interior Basin and is increasing in the Montane Cordillera; the population trend in eastern Canada is generally steady or positive. Willow Flycatcher and Yellow Warbler are declining in western ecozones+, more strongly in the Montane Cordillera and Pacific Maritime. McGillivray’s Warbler is tending negative here, declining in the Pacific Maritime but increasing in the Montane Cordillera region. Orange-crowned Warbler populations have been relatively stable here, though tending negative, but have increased in the Montane Cordillera and significantly declined in the Pacific Maritime. Lazuli Buntings have increased throughout their range in western Canada (in both Montane Cordillera and Western Interior Basin).

Figure 36. Annual indices of population change in birds of shrub/early successional habitat for the Western Interior Basin Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 36

This line graph shows annual indices of population change in birds of shrub/early successional habitat for the Western Interior Basin Ecozone+, based on data from the Breeding Bird Survey from 1973 to 2006. The abundance index shows little change in the overall trend, ranging between approximately 44 and 78 over the period.

 

Table 45. Trends in abundance of selected species of shrub/early successionalbirds that are characteristic of the Western Interior Ecozone+, based on data from the Breeding Bird Survey. The following table shows the BBS Abundance Index by decade from the 1970s to the 2000s.Footnote1
Birds of Shrub / SuccessionPopulation
Trend (%/yr)
 P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Willow Flycatcher-1.59% 6.07.85.14.5-26%
Yellow Warbler-1.19% 8.09.67.16.7-15%
MacGillivray's Warbler-0.80% 5.06.95.34.3-13%
Orange-crowned Warbler-0.20% 3.54.74.93.3-5%
Song Sparrow0.10% 8.08.47.88.56%
House Wren1.31% 1.52.63.41.718%
Spotted Towhee2.02% 3.45.37.45.355%
Lazuli Bunting2.43% 2.63.95.34.677%
Nashville Warbler5.44%*1.02.54.84.4>200%

Table 45 - 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 (1970s) and the 2000s (2000-2006). Species are listed in order from those showing most severe declines to those showing the most positive increases.

Return to table 45 footnote1referrer

 

Despite a lack of significant declines in these relatively well monitored species, there is concern about the status of several less common birds found in shrub habitats here, including Yellow-breasted Chat and Sage Thrasher, two nationally listed species at risk, and provincial blue-listed species such as Brewer's and Lark Sparrow (Partners in Flight British Columbia and Yukon, 2003). Greater Sage-grouse is now extirpated from this region.

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Grassland bird assemblage

While there are few grassland birds common enough to be monitored by BBS in this region, trends have been negative in this assemblage as a whole (Figure 37) and in individual species (Table 46). Although the data (Figure 37) show an apparent upswing in population in the last few years, it is unclear whether this reflects a true change in the population trend or simply a short-term fluctuation. These declines are part of a national and continental picture of declines among grassland birds over the past few decades. Declines in grassland and shrub/successional birds in this region reflect loss and degradation of habitat to urbanization and cropland (Partners in Flight British Columbia and Yukon, 2003). In addition to the relatively widespread species in Table 46, there are several less common grassland birds that are considered a priority for conservation attention (for example, Grasshopper Sparrow and Bobolink), including some listed as national species at risk (Barn Owl, Burrowing Owl, Short-eared Owl, and Ferruginous Hawk) (Partners in Flight British Columbia and Yukon, 2003).

Figure 37. Annual indices of population change in birds of grassland habitat for the Western Interior Basin Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 37

This line graph shows annual indices of population change in birds of grassland habitat for the Western Interior Basin Ecozone+, based on data from the Breeding Bird Survey from 1973 to 2006. The abundance index shows negative trends on the whole, from approximately 55 in the mid-1970s to 30 in the mid-2000s.

 

Table 46. Trends in abundance of selected species of grassland birds that are characteristic of the Western Interior Ecozone+, based on data from the Breeding Bird Survey. The following table shows the BBS Abundance Index by decade from the 1970s to the 2000s.Footnote1
Grassland BirdsPopulation
Trend (%/yr)
 P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Western Meadowlark-3.05%*26.324.716.712.1-54%
Vesper Sparrow-1.19% 13.711.211.78.6-37%
Savannah Sparrow-0.70% 4.03.94.92.7-34%

Table 46 - 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 (1970s) and the 2000s (2000-2006). Species are listed in order from those showing most severe declines to those showing the most positive increases.

Return to table 46 footnote1referrer

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Other open habitat bird assemblage

Other birds of open habitats have exhibited declines similar in magnitude to the grassland assemblage (Table 43, Figure 38). Individual species trends are mixed though more are negative than positive (Table 47). This assemblage contains several aerial-foraging insectivores that are declining as a group across Canada (swallows, nighthawks, and flycatchers). The trend for Violet-green Swallows is positive, though not statistically significant. This species is the only swallow in Canada showing an overall positive national trend. In contrast, Barn Swallow and Northern Rough-winged Swallow have lost more than 80% of their populations over the last three decades in the Western Interior Basin (Table 47). Bank and Cliff swallows are also showing signs of decline. The Brown-headed Cowbird has declined here and elsewhere in Canada.

Figure 38. Annual indices of population change in birds of other open habitats for the Western Interior Basin Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 38

This line graph shows annual indices of population change in birds of other open habitats for the Western Interior Basin Ecozone+, based on data from the Breeding Bird Survey from 1973 to 2006. The abundance index shows declines over the period, from 120 in 1973 to 66 in 2006.

 

Table 47. Trends in abundance of selected species of birds of other open habitats that are characteristic of the Western Interior Ecozone+, based on data from the Breeding Bird Survey. The following table shows the BBS Abundance Index by decade from the 1970s to the 2000s.Footnote1
Birds of Other Open HabitatsPopulation
Trend (%/yr)
 P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Barn Swallow-6.85%*12.510.74.71.9-85%
Northern Rough-winged Swallow-6.29%*7.75.94.01.4-82%
Common Nighthawk-3.82%n1.42.31.20.5-62%
Western Kingbird-3.44% 5.43.92.81.9-65%
Brewer's Blackbird-2.76% 38.126.521.716.8-56%
American Kestrel-2.27% 1.82.11.61.1-41%
Brown-headed Cowbird-2.18%*11.511.012.05.9-49%
Eastern Kingbird-1.78% 2.72.32.11.6-40%
Tree Swallow-0.20% 10.57.69.88.3-21%
Bullock's Oriole-0.20% 2.74.03.42.4-9%
Mountain Bluebird1.01% 1.61.61.82.025%
Violet-green Swallow1.51% 6.37.812.07.621%
Red-tailed Hawk3.05% 0.51.41.11.1106%

Table 47 - 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 (1970s) 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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Urban and suburban bird assemblage

Declines in the urban/suburban bird assemblage in the Western Interior Basin (Figure 39) are similar to other regions in Canada. Declines in the introduced European Starling (Table 48) are consistent across Canada; the species is also declining in Europe. House Finch populations are doing well throughout their Canadian range. Mourning Dove populations show a negative, though non-significant, trend here but are increasing in Canada overall, especially in the east and in the Prairies.

Figure 39. Annual indices of population change in birds of urban/suburban habitat for the Western Interior Basin Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 39

This line graph shows annual indices of population change in birds of urban/suburban habitat for the Western Interior Basin Ecozone+, based on data from the Breeding Bird Survey, from 1973 to 2006. The abundance index shows declines through the period, from approximately 190 to 110.

 

Table 48. Trends in abundance of selected species of urban/suburban birds that are characteristic of the Western Interior Basin Ecozone+, based on data from the Breeding Bird Survey. The following table shows the BBS Abundance Index by decade from the 1970s to the 2000s.Footnote1
Urban / Suburban BirdsPopulation
Trend (%/yr)
 P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
European Starling (I)-3.92%*68.760.236.722.5-67%
Mourning Dove-3.25% 8.14.43.43.0-63%
American Robin0.20% 47.345.849.647.60%
House Finch6.82%*1.44.36.47.7>200%

Table 48 - Footnotes

updated

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; (I) indicates an introduced species “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). Species are listed in order from those showing most severe declines to those showing the most positive increases.

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