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

Canada

Bird assemblages are showing significant declines in four of five habitats in Canada based on Canadian BBS results from 1968 to 2006 (Table 2). The forest bird assemblage has been essentially stable, though there has been a possible gradual decline in recent years. Regionally, there have been varying degrees of decline in forest birds in all three western ecozones+ (Pacific Maritime, Western Interior Basin, and a small non-significant decline in Montane Cordillera) and a small, non-significant decline in the Atlantic Maritime. Other ecozones+ show stable or increasing populations of forest birds. Birds of shrub/early successional habitats show a small but statistically significant decline in Canada overall, with trends varying among ecozones+ (declining significantly in the Atlantic Maritime, Boreal Shield, Boreal Plains, and Pacific Maritime; stable to slightly positive in the others). Grassland birds and birds of other open habitats show the highest level of decline (more than 40% loss of population since the 1970s). Grassland birds are declining in Canada overall, and in all ecozones+ for which there are results. With the exception of the Prairies, birds in the other open habitats assemblage are also declining in all regions in Canada. Birds in the urban/suburban assemblage are showing declines in Canada overall and consistently in all ecozones+ for which there are results.

Table 2. Trends in abundance of landbirds in Canada grouped by breeding habitat, based on data from the Breeding Bird Survey. The following table shows the BBS Abundance Index by decade from the 1970s to the 2000sFootnote1
Habitat AssemblageTrend
(%/yr)
P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Forest Birds-0.2% 153.1158.5150.4138.3-10%
Shrub/Successional-0.5%*121.1110.0110.2101.1-17%
Grassland-1.9%*81.871.757.045.7-44%
Open / Cropland-1.4%*79.079.665.845.7-42%
Urban / Suburban-0.9%*135.9126.8110.3105.6-22%

Table 2 - Footnotes

Footnote 1

In ths 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

Close to half of Canada's landbird species are associated principally with forests. Much of this forested land area is included in the vast boreal forest region. Stretching across northern Canada from the Yukon to Newfoundland, this region encompasses the Boreal Shield, Newfoundland Boreal, Boreal Plains, Boreal Cordillera, Taiga Plains, Taiga Cordillera, Taiga Shield, and Hudson Plains ecozones+. Table 3 shows trends for a cross-section of forest landbirds with reasonably good BBS trend precision (usually Standard Error(SE) < 2% per year). Because of the lack of BBS routes in most northern areas, results presented here are biased towards southern forests, within and among ecozones+. For example, the three taiga ecozones+ and the Hudson Plains Ecozone+ are greatly under-represented in trends. The Newfoundland Boreal Ecozone+ is also less represented than other regions although there are several BBS routes in that region.

Table 3. Trends in abundance of forest birds in Canada, based on data from the Breeding Bird Survey. The following table shows the BBS Abundance Index by decade from the 1970s to the 2000sFootnote1
Forest BirdsTrend
(%/yr)
P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Eastern Wood-Pewee-4.6%*1.090.890.480.29-73%
Canada Warbler-4.4%*1.080.810.470.30-72%
Wood Thrush-4.2%*1.110.630.420.30-73%
Olive-sided Flycatcher-3.9%*1.511.260.790.48-68%
Evening Grosbeak-3.6%*3.633.872.710.91-75%
Bay-breasted Warbler-3.3%*0.620.700.330.21-67%
Boreal Chickadee-3.2%*0.580.480.310.29-51%
Purple Finch-3.1%*2.111.761.000.98-54%
Veery-2.4%*7.166.484.293.37-53%
Pine Siskin-2.3%*6.989.146.813.18-54%
Rose-breasted Grosbeak-2.2%*3.063.051.681.47-52%
Dark-eyed Junco-1.5%*10.4410.698.226.47-38%
Great Crested Flycatcher-1.2%n0.941.120.890.62-34%
Cape May Warbler-0.8% 0.380.600.350.26-33%
Ovenbird-0.7%*8.238.627.156.48-21%
Least Flycatcher-0.6%n6.686.536.364.92-26%
American Redstart-0.6% 5.535.714.864.58-17%
Black-throated Green Warbler-0.6% 1.351.311.281.21-10%
Swainson's Thrush-0.5% 16.2017.0714.2314.22-12%
Tennessee Warbler-0.4% 3.595.903.153.55-1%
Yellow-bellied Flycatcher-0.4% 1.121.320.880.95-15%
Ruby-crowned Kinglet-0.3% 6.575.765.925.96-9%
Northern Parula-0.3% 0.790.880.720.75-6%
Gray Jay-0.2% 1.641.661.611.39-15%
Black-and-white Warbler-0.1% 1.662.071.731.50-9%
Northern Waterthrush-0.1% 2.332.922.332.19-6%
Blackburnian Warbler0.0% 0.700.860.770.59-16%
Magnolia Warbler0.4% 3.794.214.104.5520%
Red-eyed Vireo0.7%*14.1115.6015.6016.3216%
Winter Wren0.7% 2.832.543.453.4120%
Hermit Thrush0.8%n5.055.215.535.6311%
Yellow-rumped Warbler1.0%*6.378.748.457.9825%
Downy Woodpecker1.2%*0.390.630.570.5130%
White-breasted Nuthatch1.4%n0.160.170.200.2659%
Black-capped Chickadee1.6%*3.274.114.274.8147%
Hairy Woodpecker2.0%*0.510.630.700.7853%
Philadelphia Vireo2.4%n0.270.310.490.4668%
Red-breasted Nuthatch2.6%*1.161.722.432.42109%
Warbling Vireo2.8%*3.215.156.426.3497%
Blue-headed Vireo3.6%*0.540.700.981.26134%
Pileated Woodpecker6.5%*0.140.440.460.68>200%

Species are listed in order from those showing most severe declines to those showing the most positive increases.

Table 3 - Footnotes

Footnote 1

In ths 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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The forest landbird assemblage in Canada shows little change overall (Figure 1), as in the United States (North American Bird Conservation Initiative, U.S. Committee (NABCI-US), 2009), but there is a mix of positive, negative, and stable trends in individual species including some species whose long-term declines have caused them to be assessed as at risk by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) (for example, Canada Warbler and Olive-sided Flycatcher) (COSEWIC, 2007a), or as a conservation priority for North America (for example, Wood Thrush and Bay-breasted Warbler) (Rich et al., 2004). Forest birds include a wide variety of species that differ in habitat requirements, foraging habits, and migration pattern and thus differences in trends among individual species is not unexpected. For example, in the three boreal ecozones+, forest birds show steady or positive long-term trends as a group, although some species are showing alarming declines.

Figure 1. Annual indices of population change for forest birds in Canada, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 1

This line graph shows annual indices of population change for forest birds in Canada, based on data from the Breeding Bird Survey from 1968 to 2006. The abundance index shows little overall change, varying between 115 and 165 over the period.

 

Some 60% of Canada’s individual landbirds breed in the boreal forest (Blancher, 2003) and many species have the majority of their global breeding populations in that region. Canada’s stewardship responsibility for the boreal is high and there is a need to pay close attention to changes in bird populations. Boreal birds include year-round residents such as Boreal Chickadee, Gray Jay, and several woodpeckers and owls, but most are migratory species such as the warblers, sparrows, and flycatchers. These migratory species are influenced by factors on the wintering grounds and during migration as well as on their boreal breeding grounds. For example, the Rusty Blackbird is a boreal breeding species that migrates to the southern United States for the winter. The species has declined sharply in the last 40 years according to both CBC and BBS (Niven et al., 2004) to the extent that it was assessed as a species of Special Concern in Canada by COSEWIC (2006b). With 70% of its breeding range located in Canada, the Rusty Blackbird is a species for which Canada has a high responsibility. Results for some other species are discussed in the ecozone+ accounts below.

The three western ecozones+ all show varying degrees of decline for forest birds. In the Prairies, forest birds are increasing and may have benefitted from increased tree cover associated with human settlement. In the Mixedwood Plains Ecozone+, forest birds appear to have responded to increased forest cover resulting from succession changes in abandoned marginal farmland and are increasing as a group.

Shrub/early successional bird assemblage

The BBS does not capture trends in shrub-nesting birds from the taiga, and the results presented here represent only the southernmost portion of the northern range of some species such as Wilson’s Warbler, Orange-crowned Warbler, Fox Sparrow, and Lincoln’s Sparrow.

The overall index for birds of shrub/early-successional habitats shows a small decline (Figure 2), influenced strongly by declines in several relatively abundant shrub-nesting sparrows such as Song and White-throated (Table 4). Patterns for the assemblage vary among ecozones+ with significant declines in the Atlantic Maritime, Boreal Plains, and Boreal Shield, a non-significant decline in the Pacific Maritime, and stable or positive trends in the other ecozones+. Results for many individual species also vary across the country. The Brown Thrasher for example, with an overall loss of 60% of its population in Canada since the 1970s, is declining in the Prairies, Mixedwood Plains, Boreal Plains, and the southern portion of the Boreal Shield, but appears to be doing well in the Atlantic Maritime. Results for some other species are discussed in the ecozone+ accounts below.

Figure 2. Annual indices of population change for shrub/early successional birds in Canada, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 2

This line graph shows annual indices of population change for shrub/early successional birds in Canada, based on data from the Breeding Bird Survey from 1968 to 2006. The abundance index shows a small decline over the period, from about 120 to 100.

 

Table 4. Trends in abundance of shrub/early successional birds in Canada, based on data from the Breeding Bird Survey. The following table shows the BBS Abundance Index by decade from the 1970s to the 2000sFootnote1
Birds of Shrub / SuccessionTrend
(%/yr)
P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Wilson's Warbler-2.9%*1.781.651.070.81-54%
Brown Thrasher-2.8%*1.240.810.650.49-60%
Mourning Warbler-2.3%*3.813.892.251.99-48%
Gray Catbird-1.8%*1.871.521.061.15-39%
Chestnut-sided Warbler-1.7%*5.504.233.303.25-41%
Song Sparrow-1.3%*19.8815.2714.7413.67-31%
White-throated Sparrow-1.0%*22.0317.4817.1617.22-22%
Clay-colored Sparrow-0.1% 11.3810.6811.029.40-17%
White-crowned Sparrow1.0% 1.321.231.571.31-1%
Willow Flycatcher2.1%n0.750.970.720.74-1%
MacGillivray's Warbler2.5%*1.382.152.081.9239%
Lincoln's Sparrow3.0%*1.873.614.033.3278%
Fox Sparrow3.1%*0.711.811.471.3591%
Orange-crowned Warbler3.9%*1.442.092.832.5979%
Spotted Towhee3.9%*0.490.700.870.6942%

Species are listed in order from those showing most severe declines to those showing the most positive increases.

Table 4 - Footnotes

Footnote 1

In ths 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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Grassland bird assemblage

Results from the North American BBS indicate that grassland birds are declining throughout North America (Sauer et al., 2008; North American Bird Conservation Initiative, U.S. Committee (NABCI-US), 2009) showing steep, consistent, and geographically widespread declines. In Canada, the grassland assemblage reflects this consistent, long-term decline over the past 40 years (Figure 3, Table 5). Substantial, statistically significant declines also occur in all ecozones+ for which a trend is reported.

Figure 3. Annual indices of population change for grassland birds in Canada, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 3

This line graph shows annual indices of population change for grassland birds in Canada, based on data from the Breeding Bird Survey from 1968 to 2006. The abundance index shows steep, consistent declines over the past forty years, ranging from 89 to 43.

 

Table 5. Trends in abundance of grassland birds in Canada, based on data from the Breeding Bird Survey. The following table shows the BBS Abundance Index by decade from the 1970s to the 2000sFootnote1
Grassland BirdsTrend
(%/yr)
P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Grasshopper Sparrow-5.3%*0.310.300.120.07-78%
Bobolink-5.2%*12.5010.784.492.55-80%
Short-eared Owl-5.1%n0.660.140.130.12-82%
Eastern Meadowlark-5.1%*3.221.901.250.73-77%
Horned Lark-4.5%*20.1816.069.625.42-73%
Chestnut-collared Longspur-4.2%*3.682.511.670.49-87%
Sprague's Pipit-3.0%n1.411.020.450.43-70%
Sharp-tailed Grouse-2.3% 0.250.300.150.13-47%
Northern Harrier-1.9%*0.550.550.430.29-48%
Western Meadowlark-1.6%*15.0112.299.888.88-41%
Baird's Sparrow-1.1% 0.740.550.620.26-65%
Savannah Sparrow-0.8%*19.4616.6217.2314.52-25%
Vesper Sparrow-0.6% 8.207.897.586.87-16%
Sedge Wren1.4% 0.350.310.470.4527%
Le Conte's Sparrow2.8% 0.670.601.030.717%

Species are listed in order from those showing most severe declines to those showing the most positive increases.

Table 5 - Footnotes

Footnote 1

In ths 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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Although the major loss of native prairie grasslands occurred in the first half of the century (that is, pre-BBS and therefore not reflected in this report), loss of grasslands has continued since the beginning of the BBS and its effect is reflected in declines of grassland bird populations on the Prairies (35% loss of population since the 1970s). Losses of grassland habitat in Atlantic Maritime and the Mixedwood Plains are more recent. These were largely forested landscapes pre-settlement, so large increases in habitat for grassland birds followed the clearing of land by settlers, and declines in grassland habitat followed more recently as farms were abandoned and suitable habitat was lost. This period of habitat loss and the subsequent rapid decline in bird populations is reflected in BBS trends for these two ecozones+ (more than 60% loss of abundance since the 1970s).

Populations of most individual species are also declining in Canada, consistent within the overall assemblage decline. Some species have lost more than 50% of their populations in Canada since the 1970s (for example, Bobolink, Eastern Meadowlark, Sprague’s Pipit, Chestnut-collared Longspur, and others listed in Table 5). Reasons for declines vary among species and ecozones+ but are thought to be due to the combined effects of loss of marginal farmland to forest and more intensive use of remaining agricultural lands where most of these birds nest. Many grassland species are short-distant migrants, wintering in the United States, and are affected by similar changes in their winter habitats. The Bobolink however, migrates 8,000 km or more to winter south of the equator in South America.

Some species listed in Table 5 nest in grasslands and agricultural fields in the southern portion of their range and tundra in the northern portion (Short-eared Owl, Horned Lark, and Savannah Sparrow). The BBS trends presented in this report capture only the southern portion of their range. Two grassland birds that prefer wet habitats (Sedge Wren and Le Conte’s Sparrow) have stable or increasing trends, perhaps benefiting from habitat management actions for waterfowl.

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Other open habitat bird assemblage

Declines in birds of other open habitats (Figure 4) are likely related to changes in land use and agricultural practices resulting in a loss of habitat and habitat quality, as observed among grassland species. However, declines appear to be more recent than those in grassland birds, beginning around the mid-1980s, perhaps because these birds are more tolerant of later stages of open field succession. The Prairies Ecozone+ stands out as the only region where bird populations of other open habitats are stable rather than declining. Some species in this ecozone+ may benefit from habitat changes associated with human presence, such as increased trees or the presence of nest boxes.

Figure 4. Annual indices of population change for birds of other open habitats in Canada, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 4

This line graph shows annual indices of population change for birds of other open habitats in Canada, based on data from the Breeding Bird Survey from 1968 to 2006. The abundance index shows declines over the period, ranging between 88 and 40.

 

This assemblage contains several species of aerial-foraging insectivores (swallows, nighthawks) which are declining as a group throughout Canada. Of the eight species of swallows in Canada, the Violet-green Swallow, whose distribution is restricted to western Canada (B.C., Alberta, and Yukon), is the only one with an overall positive population trend (Table 6). Tree Swallows have declined overall but are doing well in the Mixedwood Plains and the Prairies where they may have benefitted from nest box programs. Some other species of open habitats have also fared poorly, for example the Loggerhead Shrike was assessed as Endangered in 2000 in the eastern portion of its range where its population has disappeared from Quebec and New Brunswick and there are only a few remaining breeding pairs in Ontario. The prairie subspecies has fared better, however it is also declining and was assessed as Threatened in 2004 (COSEWIC, 2004). The American Kestrel is showing large declines nationally and throughout most of the ecozones+ in which it breeds in Canada.

Table 6. Trends in abundance of birds of other open habitats in Canada, based on data from the Breeding Bird Survey. The following table shows the BBS Abundance Index by decade from the 1970s to the 2000sFootnote1
Birds of Other Open HabitatsTrend
(%/yr)
P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Loggerhead Shrike-6.5%*0.450.070.080.05-89%
Bank Swallow-4.6%*7.747.563.491.93-75%
Common Nighthawk-4.3%*0.470.450.270.10-78%
Barn Swallow-3.2%*16.6815.589.895.56-67%
Brown-headed Cowbird-2.5%*14.2511.948.936.46-55%
Eastern Kingbird-2.0%*3.623.552.701.80-50%
American Kestrel-1.7%*0.821.040.750.45-45%
Baltimore Oriole-1.4%*2.162.541.941.18-45%
Tree Swallow-0.9%*8.599.128.115.87-32%
Brewer's Blackbird0.0% 9.939.609.077.62-23%
Swainson's Hawk0.1% 0.470.540.460.33-30%
Western Kingbird1.7%n0.530.800.940.7338%
Mountain Bluebird2.2% 0.420.410.660.4916%
Violet-green Swallow2.4% 0.751.071.591.0235%
Red-tailed Hawk3.0%*0.540.881.281.19121%

Species are listed in order from those showing most severe declines to those showing the most positive increases.

Table 6 - Footnotes

Footnote 1

In ths 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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Urban and suburban bird assemblage

Though one might expect the increases in urbanization and the spread of suburbs throughout Canada to be reflected in increased populations of birds tolerant of developed landscapes, the urban/suburban assemblage shows a consistent pattern of decline both in Canada (Figure 5) and among ecozones+ for which we have results. Losses in population since the 1970s vary from 18 to 38% among ecozones+ for which there are BBS data, with a loss of 22% overall in Canada (Table 2).

Figure 5. Annual indices of population change for urban/suburban birds in Canada, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 5

This line graph shows annual indices of population change for urban/suburban birds in Canada, based on data from the Breeding Bird Survey from 1968 to 2006. The abundance index shows a consistent pattern of decline from approximately 150 to 100 over the period.

 

Both the introduced House Sparrow and European Starling are abundant but have shown substantial declines in recent decades, while Rock Pigeon populations have been relatively stable (Table 7). The declines in House Sparrow (in all ecozones+ for which there are results except in the northern Pacific rainforest) and European Starling (in all ecozones+) mirror declines in Europe (Pan-European Common Bird Monitoring Scheme, 2007). Declines in these introduced species are in contrast to many other alien species of plants and animals that are increasingly creating problems in Canada's ecosystems (for example, mussels in Great Lakes, ash borers, and other insects and plants) (Environment Canada, 2009).

Table 7. Trends in abundance of urban/suburban birds in Canada, based on data from the Breeding Bird Survey. The following table shows the BBS Abundance Index by decade from the 1970s to the 2000sFootnote1
Urban / Suburban BirdsTrend
(%/yr)
P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Chimney Swift-8.3%*0.870.350.130.08-90%
House Sparrow (I)-3.3%*27.8622.1812.3311.24-60%
European Starling (I)-3.1%*48.3336.8724.4218.73-61%
Common Grackle-2.0%*13.719.838.558.03-41%
Purple Martin-1.3% 0.700.710.730.42-40%
Northern Mockingbird-0.8% 0.020.020.020.01-69%
Chipping Sparrow-0.6%n12.7712.4811.6710.29-19%
Blue Jay-0.2% 2.142.222.142.3610%
American Robin0.4%*32.4035.6437.3835.289%
Rock Pigeon (I)0.8% 3.905.525.114.5216%
Mourning Dove1.7%*4.085.525.895.8243%
House Finch13.4%n0.100.370.990.88>200%

Species are listed in order from those showing most severe declines to those showing the most positive increases.

Table 7 - Footnotes

Footnote 1

In ths 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).

Return to table 7 footnote1referrer

In long-distance migrants such as Chimney Swift and Purple Martin, factors on the wintering grounds and during migration are also influencing populations. The Chimney Swift has experienced substantial declines throughout Canada with an overall loss of 90% of its population (Table 7) and has recently been assessed as Threatened (COSEWIC, 2007a). The Chimney Swift is one of several species of aerial-foraging insectivores showing widespread declines in Canada, perhaps indicating common causes for this group (Blancher et al., 2009; Nebel et al., 2010). In contrast, House Finch populations have expanded dramatically in the east, where they first appeared in the 1970s following introductions in eastern United States cities. The Canada-wide trend has been strongly positive in the long term; however, this species has declined over the last decade in the east.

Of course, many of the species designated as urban/suburban also exist in more natural habitats. In some regions, especially the northern ecozones+ 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 what is happening in forest and shrub/early successional habitats than in the urban/suburban landscape.

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Migration strategy assemblage

Some 274 species of landbirds regularly breed in Canada and at least 78% of these are migratory (Blancher, 2002). These Canadian summer residents spend the winters in warmer southern climes in the United States, Mexico, the West Indies, and Central and South America, and are affected by multiple factors on their breeding grounds, during migration, and on their wintering grounds.

Birds in the neotropical and short-distance migrant assemblages are showing significant overall declines in Canada (Table 8, Figure 6). The short-distance migrants, which winter in more temperate areas in southern Canada, the United States, and northern Mexico show a continual, gradual decline since the 1970s. Neotropical migrant populations appear to have increased during the 1970s, with declines beginning in the late 1980s and continuing to the present. Populations of resident birds, which include grouse, woodpeckers, chickadees, nuthatches, ravens, and cardinals, among others, have been relatively stable over the long-term.

Table 8. Trends in abundance of landbirds in Canada grouped by migration strategy, based on data from the Breeding Bird Survey. The following table shows the BBS Abundance Index by decade from the 1970s to the 2000sFootnote1
Migration StrategyTrend
(%/yr)
P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Resident-0.2% 47.348.342.845.7-3%
Short-Distance-0.8%*383.9354.3323.8291.5-24%
Neotropical-0.5%*238.6244.1221.0189.7-21%

Table 8 - Footnotes

Footnote 1

In ths 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).

Return to table 8 footnote1referrer

Figure 6. Annual indices of population change for birds in Canada grouped by migration pattern, based on data from the Breeding Bird Survey.

graph

graph

graph

Long Description for Figure 6

This graphic presents three line graphs that show annual indices of population change for birds in Canada grouped by migration pattern, based on data from the Breeding Bird Survey from 1968 to 2006. The graphs are described in the following set of points:

  1. Year-round residents: The abundance index shows little overall change, varying between 37 and 54 over the period.
  2. Neotropical migrants: The abundance index shows declines over the period, peaking in the mid-1980s around 250 and declining to 190 by 2006.
  3. Short-distance migrants: The abundance index shows declines over the period, from around 400 through the 1970s to 300 in 2006.

 

For many neotropical migrants, concerns have been raised over the loss and fragmentation of forest habitat on their wintering grounds (Robbins et al., 1989; Terborgh, 1989). In addition, spruce budworm infestations in Canada have declined over the past several decades and this may explain declines observed in several neotropical migrants that respond strongly to budworm abundance (Sleep et al., 2009). A large proportion of aerial-foraging insectivores, including most of the swallows, flycatchers, nightjars, and the Chimney Swift are neotropical migrants, and many are declining. Causes of these declines remain unclear, but changes in aerial insect populations have been suggested as one possible common factor as well as landscape changes, toxic chemicals, and climate change (Blancher et al., 2009; Nebel et al., 2010)

The short-distant migrants include many of the grassland species that are declining as a group. Seven of the nine blackbird species (excluding orioles) in Canada are short-distance migrants and six of these are showing significant long-term declines. Among other factors, blackbird populations may be affected by bird control programs in the United States that are designed to reduce populations of nuisance birds that damage crops (Dolbeer et al., 1995; COSEWIC, 2006b). Sparrows and allies are largely short-distance migrants and also show a preponderance of declines.

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Foraging assemblage

To examine patterns in populations with respect to foraging habits, birds were divided into groups based on what they eat (prey type) and where they forage (feeding substrate). Birds in the herbivore and omnivore groups have declined overall. Insectivore populations in Canada remained fairly stable until the late 1980s when they began to decline, resulting in an overall slight decline for the assemblage. Carnivore populations have been relatively stable and tending positive (Table 9, Figure 7). Patterns of population trends also vary among birds grouped by feeding substrate. Aerial and ground-foraging birds have declined. Vegetation gleaners are stable overall, but show a decline in the last several years. Trunk/bark forager populations have increased (Table 9, Figure 8).

Table 9. Trends in abundance of landbirds in Canada grouped by foraging behaviour pattern, based on data from the Breeding Bird Survey. The following table shows the BBS Abundance Index by decade from the 1970s to the 2000s

9.1 Foraging Strategy - Based on Prey TypeFootnote1
Prey TypeTrend
(%/yr)
 P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Carnivore / Piscivore0.4% 3.33.63.83.711%
Insectivore-0.3%*228.0234.4223.2196.5-14%
Herbivore / Frugivore-1.6%*32.129.320.720.9-35%
Omnivore-0.9%*407.7380.5339.5304.1-25%
9.2 Foraging Strategy - Based on Feeding Substrate
Feeding SubstrateTrend
(%/yr)
 P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Aerial-1.1%*81.386.774.653.2-35%
Vegetation0.0% 174.0177.5177.2164.0-6%
Trunk / Bark0.8%n7.07.68.68.623%
Ground-1.0%*403.1370.1321.3296.0-27%

Table 9 - Footnotes

Footnote 1

In ths 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).

Return to table 9 footnote1referrer

Figure 7. Annual indices of population change for birds in Canada grouped by prey type, based on data from the Breeding Bird Survey.

graph

graph

graph

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Long Description for Figure 7

This graphic presents four line graphs showing annual indices of population change for birds in Canada grouped by prey type, based on data from the Breeding Bird Survey, from 1968 to 2006. The graphs are described in the following set of points:

  1. Carnivores and piscivores: The abundance index shows little over all change. There is greater variance before 1985, with fluctuations between 2.7 and 4.2. From 1986 the index varies between 3.4 and 4.2 for the next twenty years.
  2. Insectivores: The abundance index remained fairly stable (around 230) until the late 1980s when they began to decline, to below 190 in 2005.
  3. Herbivores: The abundance index shows an overall decline for the period, peaking around 35 in the mid-1970s. The index declined to just above 15 in the mid-1990s, then increasing to approximately 20 in 2006.
  4. Omnivores: The abundance index shows overall declines from approximately 420 to 300 during the period.

 

Figure 8 . Annual indices of population change for birds in Canada grouped by feeding substrate, based on data from the Breeding Bird Survey.

graph

graph

graph

graph

Long Description for Figure 8

This graphic presents four line graphs showing annual indices of population change for birds in Canada grouped by feeding substrate, based on data from the Breeding Bird Survey from 1968 to 2006. The graphs are described in the following points:

  1. Aerial foragers: The abundance index shows decline over the period, peaking around 90 in the 1980s and declining to 50 in 2005.
  2. Vegetation gleanors: The abundance index is stable overall, but shows a decline in the last several years, from just under 180 in 1999 to 160 in 2006.
  3. Trunk/bark gleanors: The abundance index shows an increasing population, from just above 5 in 1968 to almost 9 in 2006.
  4. Ground foragers: The abundance index shows decline over the period, peaking above 430 in 1976, declining for thirty years to around 300.

 

Aerial foragers are predominantly insectivores (swallows, swifts, flycatchers, and others), but also include the falcons and accipiters, most of which are carnivores. The insectivorous aerial foragers stand out as a group showing large declines (Blancher et al., 2009; Nebel et al., 2010), with several declines severe enough that the species have recently been assessed as Threatened (Chimney Swift, Olive-sided Flycatcher, Common Nighthawk, and Whip-poor-will) (COSEWIC, 2007a). Within the insectivorous aerial foraging group, declines appear to be more severe and consistent among species that screen insect prey from the air while flying continuously (nightjars, swallows, and swifts) than among those that pursue individual insects during short sallies from a perch (mainly flycatchers). With the exception of the western-distributed Violet-green Swallow, numbers of all swallow species in Canada are declining. Flycatchers show a mix of declining, stable, and increasing populations. For example, the Eastern Wood-pewee has declined steadily while its western counterpart, the Western Wood-pewee, has not shown a long-term change – although it has been declining since the late 1980s. Eastern Kingbirds have undergone a large recent decline, while the Western Kingbird population has been stable to increasing. Olive-sided Flycatcher, as mentioned above, has declined severely enough that it was assessed as Threatened in 2007 (COSEWIC, 2007a). Causes for these declines are still largely unknown but may involve several factors including changes in insect abundance, changes in availability of nesting habitat (especially for Chimney Swift and Barn Swallow), climatic variation that may affect the timing and thus availability of food, and storm conditions encountered during migration (COSEWIC, 2007b), as well as habitat changes especially in other open landscapes where many of these species breed (Blancher et al., 2009).

The herbivore/frugivore/granivore group includes several northern and rare species (ptarmigans, Bohemian Waxwing) for which there are few data from the BBS and thus the overall trend for this assemblage is heavily influenced by the strong decline in the abundant House Sparrow (-3.3% per year). Individual species within this assemblage show a mix of increases and declines.

The carnivore assemblage is dominated by raptors (hawks, falcons, eagles, and owls), the majority of which are ground feeders. Because owls are nocturnal, BBS is not the best method for surveying these species. Most of the hawks, except the Northern Harrier and the Red-shouldered Hawk, have stable or positive long-term trends reflecting the overall stable assemblage pattern. Many hawks have rebounded in population since the 1960s, likely benefitting from decreased human persecution and the decreased use of DDT and other contaminants (e.g. Blancher et al., 2007).

General patterns in the omnivore group are difficult to discern as this group includes a wide variety of species (such as, thrushes, crows, sparrows, blackbirds, finches, and shrikes) with a variety of foraging strategies, although about two-thirds are ground feeders. Of the six blackbirds included in this group (excluding orioles), four are showing significant long-term declines. These blackbirds are ground feeders and all, except the Bobolink and the Yellow-headed Blackbird, are temperate migrants.

The insectivorous trunk/bark feeders group has a positive long-term trend. This group includes the migratory Pine Warbler and Black-and-white Warbler, but is dominated by resident species (several of the woodpeckers and nuthatches). These resident species appear to be doing well as a group and influence the assemblage trend.