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

Atlantic Maritime Ecozone+ (BCR 14)

Contributors: Gilles Falardeau, Kim Mawhinney, and Julie Paquet

Forests currently cover 85 and 75% of the land area of New Brunswick and Nova Scotia respectively (Busby et al., 2006), and thus the majority of the species selected as representative of this ecozone+ are forest species. The BBSis well represented in the Atlantic Maritime and results presented are generally considered representative of the ecozone+as a whole although BBSmisses some habitats such as high elevation forests and wetlands.

All assemblages except forest birds are showing statistically significant declines, with the largest declines in grassland and other open habitat birds (Table 10). These results are similar to the Boreal Shield Ecozone+, which shares many of the same species. Although we did not calculate an assemblage trend for wetland birds because few landbirds fit cleanly in this assemblage and because BBS does not cover wetland habitat well, there are several of species of interest in this region that use wetlands. The population of Nelson's Sparrow in the Atlantic Maritime, one of three disjunct breeding populations in Canada, is tending downwards (-2.9% per year). In Quebec, recent surveys of known historic sites for Nelson's Sparrow suggest a decrease in the Chaleurs Bay and Gaspé Peninsula area since the mid-1980s (Rivard et al., 2006). Rusty Blackbird, recently assessed as a Species of Special Concern in Canada (COSEWIC, 2006b) has largely disappeared (97% loss of population since the 1970s). With 70% of its breeding range located in Canada, the Rusty Blackbird is a species for which Canada has a high responsibility. Reasons for the large decline are unclear but include habitat loss and degradation in its wintering grounds in the United States, effects of climate change and environmental pollutants on the breeding grounds, and past control measures for blackbird populations (COSEWIC, 2006b). In contrast, another wetland species, the Osprey, has increased substantially (4.0% per year) according to BBS, as it has throughout much of its boreal range in Canada. Osprey are relatively tolerant of human activity and have benefitted from artificial nesting platforms (Poole et al., 2002).

Table 10. Trends in abundance of landbirds for the Atlantic Maritime 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 -0.4% 221.6218.3208.1187.1-16%
Shrub/Successional-0.6%*160.2141.9137.1134.9-16%
Grassland-3.5%*39.938.219.513.3-67%
Other Open-3.5%*64.867.036.322.6-65%
Urban / Suburban-0.6%*179.7162.0157.3154.9-14%

Table 10 - 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 cumulative effect of timber harvest in this region has been to change the age structure of the forest, increasing the early succession stands, and decreasing continuous mature stands (Dettmers, 2004; Busby et al.,2006). Softwood plantations for pulpwood exist where hardwoods once grew in New Brunswick and Nova Scotia (Busby et al., 2006). The spruce budworm cycle plays a large role in the populations of several budworm specialists (such as the Bay-breasted Warbler) as well as influencing populations of many other insectivorous birds which may respond positively to budworm outbreaks but may be negatively affected by aerial spraying to control spruce budworm (Erskine and McManus, 2005; Busby et al., 2006).

Overall, the forest assemblage appears generally stable, though tending negatively especially in the last decade (Table 10, Figure 9). There are large declines in a variety of species, while others have stable or increasing populations. The Canada Warbler, a species recently assessed as Threatened by COSEWIC(2008), has declined by 80% in the Atlantic Maritime since the 1970s (Table 11). The species is sensitive to forest fragmentation and human disturbance, and populations may have been negatively affected on both the breeding and wintering grounds by habitat loss and degradation, and a decline in spruce budworm populations (COSEWIC, 2008; Sleep et al., 2009). Declines in this species are most evident in the eastern portions of its range where the majority of the population occurs. Boreal Chickadee has also declined markedly both in this region (Table 11) and range-wide (Butcher and Niven, 2007; Bird Studies Canada, 2008), and has been designated a high priority for conservation in the region (Dettmers, 2004; Busby et al., 2006). Concerns relate to the potential effects of forest management on spruce-fir-dominated forests in the region.

Figure 9. Annual indices of population change in birds of forest habitat for the Atlantic Maritime Ecozone+, based on data from the Breeding Bird Survey.

map

Long Description for Figure 9

This line graph shows annual indices of population change in birds of forest habitat for the Atlantic Maritime Ecozone+, based on data from the Breeding Bird Survey from 1968 to 2006. The abundance index appears generally stable, varying between approximately 160 and 250 over the period. The index does show a negative trend, especially in the last decade.

 

Table 11. Trends in abundance of selected species of forest birds that are characteristic of the Atlantic Maritime 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
Canada Warbler-4.78%*2.953.121.410.60-80%
Boreal Chickadee-3.82%*1.410.790.660.55-61%
Rose-breasted Grosbeak-3.34%*5.147.152.481.37-73%
Evening Grosbeak-2.27% 12.9210.7614.014.37-66%
Purple Finch-2.18%*7.625.113.644.64-39%
Bay-breasted Warbler-1.88% 2.042.851.540.96-53%
Yellow-bellied Sapsucker-1.69%*5.853.663.164.00-32%
Ruby-crowned Kinglet-1.59%*10.677.538.395.98-44%
American Redstart-1.09%*18.5819.0315.9611.74-37%
Veery-0.90% 11.0613.289.507.37-33%
Yellow-bellied Flycatcher-0.50% 2.082.461.591.61-23%
Ovenbird-0.30% 14.3215.4513.6811.59-19%
Black-and-white Warbler-0.10% 4.054.754.353.18-21%
Black-throated Green Warbler0.40% 5.334.845.995.707%
Magnolia Warbler0.40% 12.4314.1113.0514.1814%
Northern Parula1.11%n5.095.615.876.4627%
Blackburnian Warbler2.12%n1.192.222.121.6841%
Red-eyed Vireo2.12%*14.4816.3520.7025.7678%
Black-throated Blue Warbler2.74%*0.580.560.721.41145%
Black-capped Chickadee4.60%*3.144.048.4011.03<200%
Blue-headed Vireo5.44%*1.762.544.356.67<200%

Table 11 - 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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The Atlantic Maritime region in Canada and in neighbouring United States supports over 90% of the world’s breeding population of Bicknell’s Thrush, one of the rarest songbirds in North America. Bicknell’s Thrush was assessed by COSEWICas Special Concern in 1999 but its status was revised to Threatened in 2009 (COSEWIC, 2010). This bird lives in high-elevation coniferous forests and is particularly susceptible to climate change, which may result in shifts in high-elevation vegetation zones. Other threats include habitat loss and degradation on both the breeding and wintering grounds, squirrel predation at nests, and environmental contaminants (Rimmer et al., 2001; McFarland et al., 2008; COSEWIC, 2009). Wind farms, often located in high-elevation areas, are increasing in Quebec and the Maritimes (CanWEA, 2010) and may also be a future concern. Because of its scarcity and remote breeding habitat, Bicknell’s Thrush is rarely recorded by the BBS; however, special surveys in the Maritimes over the last seven years have indicated that it has declined considerably (Campbell et al., 2008), a finding supported by early results of the second Maritime Breeding Bird Atlas (Bird Studies Canada, 2008), and by similar declines observed in Appalachian forests of the northeastern United States (King et al., 2008).

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Shrub/early successional bird assemblage

A large portion of the forested land in Atlantic Maritime is in early succession. The overall slightly negative trend in this assemblage (Figure 10) is influenced by the strong declines in abundant species such as White-throated Sparrow and Song Sparrow (Table 12), both of which show varying levels of decline elsewhere in Canada. Increases in early successional forest habitat (Rosenberg and Hodgman, 2000) have favoured generalist species such as Nashville Warbler, Yellow Warbler, and Chestnut-sided Warbler. Despite this increase in habitat, other species are showing declines. Reasons for the decline in White-throated Sparrow are difficult to determine; the species responds positively to open forests and may also follow spruce budworm fluctuations.

Figure 10. Annual indices of population change in birds of shrub/early successional habitat for the Atlantic Maritime Ecozone+, based on data from the Breeding Bird Survey.

map

Long Description for Figure 10

This line graph shows the annual indices of population change in birds of shrub/early successional habitat for the Atlantic Maritime Ecozone+, based on data from the Breeding Bird Survey from 1968 to 2006. The abundance index shows a slightly negative trend, from roughly 175 to 125 over the period.

 

Table 12. Trends in abundance of selected species of shrub/early successional birds that are characteristic of the Atlantic Maritime 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-2.86%*3.322.641.531.28-62%
White-throated Sparrow-1.78%*50.0635.4530.4430.01-40%
Mourning Warbler-1.39%*2.302.581.921.40-39%
Song Sparrow-0.90% 33.9328.5126.5526.75-21%
Chestnut-sided Warbler0.00% 5.734.754.655.59-3%
Common Yellowthroat0.10% 20.8021.4821.4921.373%
Alder Flycatcher0.20% 14.7915.8816.7815.122%
Nashville Warbler0.30% 5.244.794.796.0415%
Yellow Warbler0.30% 8.349.499.668.27-1%
American Goldfinch0.50% 11.9410.8213.5714.9425%

Table 12 - 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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Grassland bird assemblage

Grassland birds are showing alarming declines in the Atlantic Maritime (Figure 11) consistent with declines in other ecozones+ in Canada. In the Atlantic Maritime, declines started in the mid-1980s and continued until an apparent levelling off in the last few years, whereas the Prairies and Mixedwood Plains ecozones+ show more consistent declines since the 1970s. Vesper Sparrow, Bobolink, and Eastern Meadowlark populations in the Atlantic Maritime have declined by over 75% since the 1970s (Table 13). The increasing population of Northern Harrier may in part reflect its use of large marshes and fens as well as grassland in this ecozone+. The decline in grassland birds is thought to be due to the abandonment of marginal farmland and subsequent return of grassland habitat to forest (Erskine and McManus, 2005). Earlier hay-cutting may also be an important negative factor in the nesting success of these birds, resulting in population declines (Nocera et al., 2005; Busby et al., 2006).

Figure 11. Annual Indices of population change in birds of grassland habitat for the Atlantic Maritime Ecozone+, based on data from the Breeding Bird Survey.

map

Long Description for Figure 11

This line graph shows annual indices of population change in birds of grassland habitat for the Atlantic Maritime Ecozone+, based on data from the Breeding Bird Survey from 1968 to 2006. The abundance index shows alarming declines, starting in the mid-1980s with index values around 45 to the mid-2000s when values decline to almost 10.

 

Table 13. Trends in abundance of selected species of grassland birds that are characteristic of the Atlantic Maritime 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
Vesper Sparrow-7.78%*0.630.320.090.08-88%
Bobolink-5.64%*22.8524.757.873.69-84%
Eastern Meadowlark-4.59% 0.640.600.310.16-75%
Savannah Sparrow-1.59% 14.5010.7610.178.57-41%
Northern Harrier5.44%n0.060.220.300.16185%

Table 13 - 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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Other open habitat bird assemblage

The amount of other open habitat has declined in the Atlantic Maritime, likely due to a decrease in the number of farms, especially small-scale farms. Fields that are no longer cleared are reverting to forest (Busby et al.,2006). Nevertheless, open habitat is still an important part of the landscape; on Prince Edward Island, farmland represents approximately 50% of the landscape (Busby et al., 2006). Birds of open habitat show similar declines to grassland birds (Figure 12, Table 14). This likely results from the loss of habitat beginning in the mid-1980s when farming began to decrease, with intensification of agricultural practices on remaining farms. This assemblage includes many aerial-foraging insectivores that are declining as a group here and in other regions of Canada (Blancher et al., 2009; Nebel et al., 2010).

Figure 12. Annual indices of population change in birds of other open habitats for the Atlantic Maritime Ecozone+, based on data from the Breeding Bird Survey.

map

Long Description for Figure 12

This line graph shows annual indices of population change in birds of other open habitats for the Atlantic Maritime Ecozone+, based on data from the Breeding Bird Survey from 1968 to 2006. The abundance index generally varies between 60 and 80, until 1985 where it declines to approximately 20 in 2006.

 

Table 14. Trends in abundance of selected species of birds of other open habitats that are characteristic of the Atlantic Maritime 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 Open HabitatsPopulation
Trend (%/yr)
 P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Bank Swallow-6.48%*13.2617.506.131.56-88%
Barn Swallow-5.45%*22.0420.068.114.09-81%
Common Nighthawk-4.30%n0.370.420.190.10-73%
Baltimore Oriole-3.73%*0.400.980.210.14-64%
Eastern Kingbird-2.57%*1.622.120.920.68-58%
Cliff Swallow-1.98%n4.605.193.702.34-49%
Tree Swallow-1.69%*16.2119.1114.399.03-44%
American Kestrel-0.10% 0.340.420.430.30-12%

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

Table 14 - 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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Urban and suburban bird assemblage

Urban areas are generally expanding in this region and this might be expected to result in an increase in urban-associated bird species. However, the urban assemblage is showing a small negative trend (Figure 13), resulting mainly from declines in two abundant introduced species, European Starling and House Sparrow, as well as a sharp decline in Chimney Swift (Table 15). The decline in Chimney Swift, assessed as Threatened by COSEWIC(2007b), may be partially related to the capping of chimneys which makes them unsuitable for nesting and roosting. The Chimney Swift is one of several species of aerial-foraging insectivores showing widespread declines in Canada, so other factors may be involved. As in other ecozones+, urban birds may be affected by increased exposure to contaminants, increased predation from domestic cats, and fewer green spaces. Rock Pigeon, another introduced species, and Mourning Dove both show large increases in populations and may be responding to milder winters and an increasing number of bird feeders.

Figure 13. Annual indices of population change in birds of urban/suburban habitat for the Atlantic Maritime Ecozone+, based on data from the Breeding Bird Survey.

map

Long Description for Figure 13

This line graph shows annual indices of population change in birds of urban/suburban habitat for the Atlantic Maritime Ecozone+, based on data from the Breeding Bird Survey from 1968 to 2006. The abundance index shows a small negative trend, decreasing from around 200 to 150 during the period.

 

Table 15. Trends in abundance of selected species of urban/suburban birds that are characteristic of the Atlantic Maritime 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
Chimney Swift-7.23%*2.721.200.490.37-87%
House Sparrow-6.95%*15.928.963.621.78-89%
European Starling-1.78%*56.3844.0238.3032.87-42%
Common Grackle-0.50% 29.3625.6026.4927.13-8%
Chipping Sparrow-0.30% 10.7912.1110.0410.62-2%
Blue Jay-0.10% 4.694.634.925.1610%
American Robin0.00% 60.3959.5761.1559.55-1%
Rock Pigeon4.71%*1.883.196.305.41187%
Mourning Dove20.32%*0.090.473.597.24<200%

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

Table 15 - 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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