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

Prairies Ecozone+ (BCR 11)

Contributor: Brenda Dale

The Prairies is dominated by grassland habitat and is the heart of range for many grassland birds in Canada; therefore, most of the species selected as representative of this ecozone+ are from the grassland assemblage. The BBS has shown that grassland birds are declining more rapidly than any other group of birds in North America (Sauer et al., 2000; Sauer et al., 2008; North American Bird Conservation Initiative, U.S. Committee (NABCI-US), 2009) and this is strongly reflected in the results both for Canada as a whole and for the Prairies (Table 33). The dominance of grassland birds in the Prairies highlights the importance of the general decline seen in these species in relation to the health of this ecozone+.

Table 33. Trends in abundance of landbirds for the Prairies 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 1.3%*16.321.923.022.035%
Shrub0.0% 81.579.286.578.2-4%
Grassland-1.6%*239.1223.2183.9154.7-35%
Other / Open0.1% 128.0129.4136.2118.1-8%
Urban-0.9%n129.9122.794.9106.7-18%

Table 33 - 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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BBS routes in the Prairies tend to be located in agricultural areas where there is a good road network and where there has been substantial loss of native grassland to agriculture. The remaining areas of extensive grassland in the Prairies are concentrated in a relatively small area, often with poor road access, so there is sparse coverage by BBS in these remaining native grasslands where the grassland bird density is high.The Grassland Bird Monitoring (GBM) program (e.g. Dale et al., 2005), which began in 1996, provides supplemental data to the BBS. GBM surveys are located in areas of southeastern Alberta and southwestern Saskatchewan where grassland is still common. Comparing or combining trends between the BBS and the GBM can help corroborate population changes and determine possible reasons for declines and distribution of losses (for example, whether declines are in core or peripheral parts of the species range). We present results for the BBS in the tables below but include results from GBM where appropriate in the discussion.

Birds of other open and shrub/early successional habitats are relatively stable in the Prairies Ecozone+ (Table 33). The forest bird assemblage shows a positive trend while urban/suburban birds are decreasing as a group. The latter pattern is consistent with other ecozones+ and across Canada as a whole. Birds of forest, urban, and shrub/early successional habitats are a relatively small component of prairie avifauna.

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Grassland bird assemblage

A consistent, long-term decline in grassland birds is evident, with a loss of 35% of birds since the 1970s (Figure 27, Table 33). Nine of the 13 selected representative species show varying rates of population decline (Table 34).

Figure 27. Annual indices of population change in birds of grassland habitat for the Prairies Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 27

This line graph shows annual indices of population change in birds of grassland habitat for the Prairies Ecozone+, based on data from the Breeding Bird Survey from 1969 to 2006. The abundance index shows consistent, long-term decline, from approximately 270 in 1969 to 140 in 2001. Trends increased during the mid-2000s, up to 170.

 

Table 34. Trends in abundance of grassland birds for the Prairies 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
McCown's Longspur-11.0%*6.102.050.770.24-96%
Chestnut-collared Longspur-5.4%*18.8714.807.972.58-86%
Short-eared Owl-5.0%n0.470.210.090.10-78%
Sharp-tailed Grouse-4.0%*1.491.730.470.53-64%
Sprague's Pipit-3.8%*6.685.352.092.04-69%
Horned Lark-3.3%*81.1577.0348.8131.38-61%
Northern Harrier-3.0%*2.071.701.140.92-55%
Western Meadowlark-1.3%*60.2149.2543.2343.67-27%
Baird's Sparrow-1.1% 3.532.883.101.39-61%
Vesper Sparrow0.8% 22.0026.8827.0328.4129%
Savannah Sparrow1.0%*27.7729.3235.1033.9222%
Le Conte's Sparrow1.6% 1.141.222.011.2611%
Sedge Wren5.7%*0.310.230.700.94199%

Table 34 - 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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The past conversion of native grassland to agriculture has resulted in a loss of approximately 75% of grassland in prairie Canada (Statistics Canada, 1993). This loss has slowed in recent years but not stopped; 10% of remaining native grassland was lost between 1985 and 2001 in some areas (Watmough and Schmoll, 2007). Losses of native grassland to urban and suburban development, especially around large urban areas, have increased. Although not as extensive as losses to agriculture, these losses can be locally devastating. Current grassland bird populations are also impacted by habitat degradation and changed landscape configuration caused by the intensification of grazing, expansion of woody cover due to fire suppression, continued fragmentation, and invasion of natural habitats by non-native plants associated with linear development such as roads, trails, and pipelines (Askins et al., 2007).

Some of the species (Horned Lark, McCown's Longspur, and Upland Sandpiper) showing long-term declines (Table 34) were not declining on recent (1996 to 2006) BBS or GBM routes that have more than 50% grassland, but were declining on routes with less grass. Habitat loss or fragmentation may be a major factor for these species as they are still doing well where habitat is common and in large blocks. Other species are showing large declines (for example, Sprague’s Pipit) where grassland remains common; this may reflect decreased habitat quality. Sprague’s Pipit is area sensitive (Davis, 2004) and thus occurs in lower numbers near linear development (Sutter et al.,2000; Hamilton, 2010) or where non-native plants occur (Sutter and Brigham, 1998).

The relative stability of the grassland guild in the past decade (Figure 27) reflects the strong influence of some common (such as, Vesper Sparrow and Savannah Sparrow) or wet meadow associated (such as, LeConte’s Sparrow and Sedge Wren) grassland birds encountered on BBS. These species are more widely distributed and are not restricted to the Great Plains, and may be tolerant of, or even helped by, taller non-native plant species. They may benefit from increased linear development and associated non-native vegetation and from several farm programs in Canada and the United States that have planted tall, non-native grasses on croplands thereby creating new habitat (Johnson and Ruttan, 1993; McMaster and Davis, 2001; Dale et al., 2005). Sprague’s Pipit, McCown’s Longspur, Chestnut-collared Longspur, and Baird’s Sparrow are declining species that need moderate or short, preferably native, cover, and make little or no use of planted cover (McMaster and Davis, 2001). Although some grassland birds will use areas planted in hay, 50 to 60% of ground nests, eggs, young, and fledglings can be lost during a haying operation (Frawley, 1989; Bollinger et al., 1990). One large study found 100% nest failure from haying operations because any nests that remained after hay cutting were abandoned (Perlut et al., 2006).

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Forest bird assemblage

The forest assemblage shows a positive trend with an overall increase of 35% since the 1970s (Figure 28, Table 33). This assemblage has benefitted from increased forest habitat in the Prairies as a result of trees associated with human settlement including farms, and the southern expansion of parkland habitat (Anderson and Bailey, 1980; Peltzer and Wilson, 2006). The forest assemblage includes several species that were presumably rare in pre-settlement times but are tolerant of human disturbances in and near populated areas (Table 35).

Figure 28. Annual indices of population change in birds of forest habitat for the Prairies Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 28

This line graph shows annual indices of population change in birds of forest habitat for the Prairies Ecozone+, based on data from the Breeding Bird Survey from 1969 to 2006. The abundance index shows a positive trend from approximately 13 to 24 over the period.

 

Table 35. Trends in abundance of forest birds for the Prairies 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
Red-eyed Vireo0.8% 3.374.533.413.494%
Black-capped Chickadee1.9% 0.821.080.821.0528%
Least Flycatcher2.1%*4.126.548.116.7062%
Warbling Vireo3.1%*2.674.785.835.49106%
Merlin9.4%*0.010.050.200.26>200%

Table 35 - 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 trend for the shrub/early successional assemblage is relatively stable (Figure 29) with individual species showing a mix of increases and decreases (Table 36). Brown Thrasher and Song Sparrow are showing declines here as elsewhere in Canada. In the Prairies, Brown Thrasher declines may be related to changes in land-use practices that can result in a reduction in hedgerows and shelterbelts and increased predation (Cavitt and Haas, 2000). Population changes in American Goldfinch and Yellow Warbler vary across Canada but are showing increases in this ecozone+.

Figure 29. Annual indices of population change in birds of shrub/early successional habitat for the Prairies Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 29

This line graph shows annual indices of population change in birds of shrub/early successional habitat for the Prairies Ecozone+, based on data from the Breeding Bird Survey from 1969 to 2006. The abundance index shows relatively stable populations during the period, varying between 70 and 95.

 

Table 36. Trends in abundance of shrub/early successional birds for the Prairies 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
Brown Thrasher-2.4% 2.411.461.601.12-54%
Song Sparrow-1.0%*11.267.979.328.28-26%
Clay-colored Sparrow-0.9%*37.5630.8629.5626.50-29%
Gray Catbird-0.1% 1.902.101.652.1614%
House Wren1.0%n12.9217.0718.9016.4427%
Common Yellowthroat1.0% 2.182.402.802.5517%
American Goldfinch1.1%*5.117.958.716.9837%
Yellow Warbler1.9%*6.707.2510.7210.9864%

Table 36 - 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

Population levels of birds of other open habitat are relatively stable overall (Table 33, Figure 30) but individual species show a mix of increases and decreases (Table 37) which may depend upon whether the species benefits from huNumenius amman changes to the landscape (for example, an increase in trees or the presence of nest boxes) or not. The prairie population of Loggerhead Shrike, a bird of open habitat assessed as Threatened in 2004 (COSEWIC, 2004), shows a continued and strong decline in population. This species is affected by conversion of agricultural land to urban development as well as by more intensive agricultural practices that, among other things, remove hedgerow and shrubs near fields. American Kestrel shows a large decline in this and most of the other ecozones+, in which it breeds. Several swallow species, a group that is declining in Canada overall, are doing well in the Prairies (Cliff Swallow, Tree Swallow, and Northern Rough-winged Swallow). Tree Swallow and Mountain Bluebird may have benefited from nest box programs. Tree Swallow and others (for example, Red-tailed Hawk and Western Kingbird) may also have benefitted from an increased number of trees on the agricultural landscape.

Figure 30. Annual indices of population change in birds of other open habitats for the Prairies Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 30

This line graph shows annual indices of population change in birds of other open habitats for the Prairies Ecozone+, based on data from the Breeding Bird Survey from 1969 to 2006. The abundance index shows relatively stable population levels over the period, varying approximately between 100 and 160.

 

Table 37. Trends in abundance of birds of other open habitats for the Prairies 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
Loggerhead Shrike-5.0%*1.780.380.410.31-83%
American Kestrel-1.8% 0.520.780.480.27-49%
Barn Swallow-1.5%*16.7817.0714.509.70-42%
Bank Swallow-1.3% 4.345.233.623.43-21%
Swainson's Hawk-1.1% 2.303.012.231.69-26%
Eastern Kingbird-0.5% 6.716.466.965.62-16%
Brown-headed Cowbird-0.5% 27.3631.0825.4924.05-12%
Gray Partridge-0.4% 0.941.160.690.91-4%
Baltimore Oriole-0.3% 3.835.004.522.78-27%
Brewer's Blackbird0.2% 27.7221.5624.7726.75-4%
Western Kingbird1.4% 2.103.003.243.3358%
Cliff Swallow2.0% 25.8225.0439.5627.707%
Tree Swallow2.1%n4.174.286.576.1648%
Red-tailed Hawk3.3%*1.372.193.463.51156%
Mountain Bluebird3.9%*0.431.111.861.01135%

Table 37 - 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 37 footnote1referrer


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Urban and suburban bird assemblage

The urban/suburban bird assemblage includes 13 species found across Canada, nine of which are found in the Prairies Ecozone+ and included in this analysis. Of these, three are non-native species introduced to Canada, House Sparrow, European Starling, and Rock Pigeon, the others are native species that are generally tolerant of human-modified habitats but also occur within their natural habitat (e.g., American Robin).

Urban/suburban birds are declining over the long-term in the Prairies, mainly due to declines during the 1980s to mid-1990s (Figure 31, Table 38). The overall negative trend for this group is influenced by strong declines in abundant House Sparrow and European Starling up to the 1990s (Table 38); these are consistent with declines observed in other regions of Canada. The reasons for decline are unclear but may reflect loss of nesting habitat due to changes in building design and loss of older buildings, and increased predation from cats and avian predators such as Merlin, a species that has substantially increased in urban areas (Warkentin et al., 2005). Merlin is included in the forest assemblage, however, in the Prairies Ecozone+, they might be better associated with the urban/suburban assemblage. Increases in American Robin may be in part due to increases in forest habitat (Table 38).

Figure 31. Annual indices of population change in birds of urban/suburban habitat for the Prairies Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 31

This line graph shows annual indices of population change in birds of urban/suburban habitat for the Prairies Ecozone+, based on data from the Breeding Bird Survey from 1969 to 2006. The abundance index shows populations are declining in the long-term, although the indices vary widely through the period, between approximately 170 and 70.

 

Table 38. Trends in abundance of urban/suburban birds for the Prairies 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)-2.5%*32.5122.6516.0218.03-45%
House Sparrow (I)-1.9%*70.1063.3638.6443.16-38%
Rock Pigeon (I)0.4% 8.3710.958.558.825%
Mourning Dove1.3%*8.5813.3012.3212.0240%
American Robin2.8%*6.9810.1513.1514.86113%

Table 38 - 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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