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

Boreal Plains Ecozone+(southern half of BCR 6)

Contributor: Kevin Hannah

BBS data are concentrated largely in the developed part of the Boreal Plains Ecozone+ where much of the landscape alteration and habitat loss is occurring. Parts of the ecozone+ that are still relatively intact and have experienced relatively little change are less well covered or not covered by BBS. The results presented are based on data between 1971 and 2006 because few BBS routes were run in earlier years.

The Boreal Plains is largely a forested region, thus the majority of species selected as representative of this ecozone+ were from the forest and shrub/early successional assemblages. Forest birds as a whole have remained stable over the long-term in the Boreal Plains while birds in all other assemblages have declined (Table 27).

Table 27. Trends in abundance of landbirds for the Boreal Plains 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 Birds0.0% 107.1134.6115.4108.61%
Shrub / Successional-1.2%*170.2151.7142.2117.5-31%
Grassland Birds-1.7%n58.346.742.136.1-38%
Open / Agricultural-2.6%*75.381.469.432.2-57%
Urban / Suburban-1.3%*81.579.465.357.5-29%

Table 27 - 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

While the overall trend for forest birds has remained fairly stable (Figure 22), individual species show a mix of increases, decreases, and relatively stable populations (Table 28). The Western Wood-pewee shows a non-significant decline of more than 50% of its population over the survey period, similar to declines in its eastern counterpart, the Eastern Wood-pewee. The Western Wood-pewee is declining across its North American range (Sauer et al.,2008) and in some Canadian ecozones+, although its overall Canadian trend shows no change in population. This species undergoes a long migration to winter in the tropics and is exposed to threats during migration and on its tropical forest wintering habitat as well as on its Canadian breeding grounds. The decline of over 50% of the population of Warbling Vireo since the 1970s is in contrast to increases in other regions and a strong increase in Canada overall. On the other hand, populations of Swainson’s Thrush, Black-and-white warbler and Pileated Woodpecker show large, significant increases and appear to be faring well in this ecozone+.

Figure 22. Annual indices of population change in birds of forest habitat for the Boreal Plains Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 22

This line graph shows annual indices of population change in birds of forest habitat for the Boreal Plains Ecozone+, based on data from the Breeding Bird Survey from 1971 to 2006. The abundance index shows the overall trend has remained fairly stable over the period, ranging between approximately 80 and 160.

 

Table 28. Trends in abundance of selected species of forest birds that are characteristic of the Boreal Plains 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
Forest BirdsPopulation
Trend (%/yr)
 P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Ruffed Grouse-5.92%*2.40.80.30.3-87%
Warbling Vireo-2.96%*6.86.64.42.9-58%
Western Wood-Pewee-2.27% 2.85.13.51.2-57%
Pine Siskin-1.39% 4.110.66.53.6-12%
Least Flycatcher-0.90%n11.814.313.08.9-25%
Yellow-bellied Sapsucker-0.10% 2.22.21.41.6-27%
Red-eyed Vireo0.90% 18.625.821.525.939%
Rose-breasted Grosbeak1.41% 2.23.12.53.142%
Black-capped Chickadee1.41% 2.63.73.53.637%
Gray Jay2.02% 1.72.72.72.016%
Hairy Woodpecker2.53% 0.40.80.80.891%
Swainson's Thrush2.53%*4.210.57.48.395%
Black-and-white Warbler3.56%*0.50.60.71.2157%
Pileated Woodpecker7.14%*0.00.20.30.61495%

Table 28 - 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

The shrub/early successional assemblage has experienced a fairly consistent, long-term decline (Figure 23, Table 29). More species are showing negative trends than positive and there are several with large, long-term declines of over 40% of their populations. Decreasing shrub habitat as it matures into young forest may help explain the apparent decline in shrub/early successional species and the increases in species that inhabit young forest. For example, declines in Mourning Warbler, Common Yellowthroat, Song Sparrow, Alder Flycatcher, and Clay-colored Sparrow are occurring at the same time as increases in birds of young forests, such as Red-eyed Vireo, Rose-breasted Grosbeak, Connecticut Warbler, and Black-and-white Warbler.

Figure 23. Annual indices of population change in birds of shrub/early successional habitat for the Boreal Plains Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 23

This line graph shows annual indices of population change in birds of shrub/early successional habitat for the Boreal Plains Ecozone+, based on data from the Breeding Bird Survey from 1971 to 2006. The abundance index shows consistent, long-term decline over the period, from approximately 180 in the early 1970s to 120 in 2006.

 

Table 29. Trends in abundance of selected species of shrub/early successional birds that are characteristic of the Boreal Plains 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
Gray Catbird-3.73%*2.21.30.90.7-67%
Mourning Warbler-3.25% 4.24.81.81.8-57%
Common Yellowthroat-3.05%*13.611.37.05.9-57%
Song Sparrow-2.47%*34.421.419.715.9-54%
Alder Flycatcher-2.27%*16.217.311.68.5-47%
American Goldfinch-2.08%*7.39.76.64.0-45%
Clay-colored Sparrow-1.98%*41.130.127.022.9-44%
House Wren-0.80% 11.312.913.38.4-25%
Yellow Warbler0.30% 12.315.015.612.63%
White-throated Sparrow0.30% 20.018.819.420.21%
Connecticut Warbler2.63% 0.62.01.31.4110%
Lincoln's Sparrow4.92%n2.810.310.89.3>200%

Table 29 - 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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Grassland bird assemblage

As in other parts of Canada, grassland birds are declining as a group in the Boreal Plains (Figure 24, Table 30) although the trend appears more positive in the last decade. Bobolink, Northern Harrier, Western Meadowlark, and Vesper Sparrow all show significant long-term declines with estimated losses of more than 60% of their populations since the 1970s (Table 30).

Figure 24. Annual indices of population change in birds of grassland habitat for the Boreal Plains Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 24

This line graph shows annual indices of population change in birds of grassland habitat for the Boreal Plains Ecozone+, based on data from the Breeding Bird Survey from 1971 to 2006. The abundance index shows significant declines during the period, from over 70 in the mid-1970s to 30 in 2002. The trend appears more positive in the last decade, increasing to around 40 by 2006.

 

Table 30. Trends in abundance of selected species of grassland birds that are characteristic of the Boreal Plains 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
Bobolink-6.85%*2.71.70.40.4-85%
Northern Harrier-5.82%*1.10.90.40.2-79%
Western Meadowlark-4.50%*8.45.43.12.5-71%
Vesper Sparrow-3.54%*17.89.27.16.6-63%
Le Conte's Sparrow-1.69% 4.12.93.22.0-51%
Savannah Sparrow0.10% 22.025.926.320.9-5%

Table 30 - 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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Other open habitat bird assemblage

As observed elsewhere in Canada, there is an overall decline in birds of other open habitat (Figure 25, Table 31). More species are decreasing than increasing, with six species showing large declines of over 50% of their population (Table 31). Many of the aerial-foraging insectivores that are declining (for example, Tree Swallow, Barn Swallow, and Eastern Kingbird) are declining across much of Canada.

Figure 25. Annual indices of population change in birds of other open habitats for the Boreal Plains Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 25

This line graph shows annual indices of population change in birds of other open habitats for the Boreal Plains Ecozone+, based on data from the Breeding Bird Survey from 1971 to 2006. The abundance index shows an overall decline during the period, from over 100 in 1982 to below 25 in 2003.

 

Table 31. Trends in abundance of selected species of birds of other open habitats that are characteristic of the Boreal Plains 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
Eastern Kingbird-7.50%*5.43.01.40.6-89%
Brewer's Blackbird-4.69%*24.221.713.15.4-78%
Baltimore Oriole-4.50%*4.35.32.81.1-74%
Mountain Bluebird-3.82% 1.20.40.40.4-70%
Barn Swallow-3.54%*12.814.110.74.1-68%
Brown-headed Cowbird-2.47% 12.18.98.85.1-58%
American Kestrel-0.90% 1.41.81.51.0-28%
Tree Swallow-0.40% 5.14.54.64.2-17%
Red-tailed Hawk1.71% 1.11.82.01.641%

Table 16 - 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

Consistent with many other ecozones+, the urban/suburban assemblage has shown an overall decline (Figure 26) driven in large part by declines in two introduced species, House Sparrow and European Starling (Table 32). In this region, where human habitation influences a relatively small proportion of the landscape, change or lack of change in species such as Chipping Sparrow, American Robin, and Blue Jay may be more a reflection of changes in their forest and shrub/early successional habitats.

Figure 26. Annual indices of population change in birds of urban/suburban habitat for the Boreal Plains Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 26

This line graph shows annual indices of population change in birds of urban/suburban habitat for the Boreal Plains Ecozone+, based on data from the Breeding Bird Survey from 1971 to 2006. The abundance index shows an overall decline, varying around 80 through the 1970s and 1980s, then declining to around 50 in the mid-2000s.

 

Table 32. Trends in abundance of selected species of urban/suburban birds that are characteristic of the Boreal Plains 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
House Sparrow (I)-7.50%*21.014.25.32.7-87%
European Starling (I)-4.40%*20.217.79.85.8-71%
Mourning Dove-3.15%*5.36.14.62.1-61%
Common Grackle-2.08% 2.02.01.60.9-55%
Chipping Sparrow-1.69% 19.516.611.612.9-34%
Rock Pigeon (I)1.01% 1.54.43.12.459%
American Robin1.21%*18.922.626.524.932%
Blue Jay2.33% 0.51.10.90.973%

Table 32 - 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; (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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