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

Boreal Shield Ecozone+(BCRs 8 and 12, minus Newfoundland Boreal)

Contributors: Mike Cadman and Lyle Friesen

The Boreal Shield has a high diversity of bird species including year-round residents, such as Boreal Chickadee and Gray Jay, as well as many migratory species that breed in the boreal each summer and then migrate southward over much of the western hemisphere. Large portions of many species’ global populations are represented in Canada’s boreal forest, including the Boreal Shield. Sparrows, warblers, and thrushes account for more than half of all boreal landbirds. About 50% of the world’s population of the 37 warbler species that live in Canada live in the boreal forest (Blancher, 2003). Boreal landbirds are highly migratory; an estimated 93% of them leave the boreal each fall to winter in the United States, Mexico, the West Indies, and Central and South America (Blancher, 2003). Forest habitat dominates the Boreal Shield Ecozone+, and thus forest birds form the majority of species selected as representative for the ecozone+. Birds of open habitats are a minor part of the avifauna, mainly in the southern part of the ecozone+.

Much of the coverage from the BBS in the Boreal Shield is in the southern portion of Ontario and Quebec, with few samples in the more northern shield and areas outside of Ontario and Quebec. Agricultural areas in the region are relatively well covered by BBS because they tend to be accessible by roads and are found in the southern parts of the region.

Table 22 shows trends in abundance for landbird assemblages. BBSresults show declines for birds of other open and shrub/early successional habitats. An assemblage trend for wetland landbirds is not included because few landbirds fit cleanly into this assemblage and because the BBS does not cover wetland habitat well. Nevertheless, it is worth noting that the Rusty Blackbird, assessed as a species of Special Concern in 2006 (COSEWIC, 2006b), has declined steeply in the surveyed portions of this region in recent decades, according to the BBS. The forest birds assemblage shows close to stable populations, although the trends for individual species within this group are diverse, ranging from large declines to large increases. The shrub/early successional assemblage is also relatively stable but exhibits a negative trend. The results for forest and shrub/early successional assemblages are strikingly similar to the same assemblages in the Atlantic Maritime Ecozone+, both regions sharing many of the same species.

Table 22. Trends in abundance of landbirds for the Boreal Shield 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-0.2% 208.0213.7206.6186.1-11%
Shrub / Successional-0.7%*164.4143.3138.8129.7-21%
Open / Agricultural-4.0%*42.842.521.511.3-74%

Table 22 - 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).

Return to table 22 footnote1referrer

Another source of data on northern forest birds in this ecozone+ is the Atlas of the Breeding Birds of Ontario (Cadman et al., 2007). Changes observed in northern forest birds between the first (1981-1985) and the second (2001-2005) atlas tend to be more positive than BBSresults, which as described above, are more representative of southern portions of the Boreal Shield.

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Forest bird assemblage

The BBS forest assemblage pattern has been relatively stable (Figure 19) but individual species show a mix of increasing, decreasing, and stable populations (Table 23). Table 24 presents the results from the Atlas of the Breeding Birds of Ontario and is included for the forest bird assemblage because it provides better coverage for the northern forests than the BBS. These data show that there was an increase in the probability of detecting most forest birds in the Boreal Shield in 2001-2005 compared with the 1981-1985 time period, although increased efficiency of Atlas coverage in 2001-2005 cannot be ruled out as an explanation (Cadman et al., 2007).

Figure 19. Annual indices of population change in birds of forest habitat for the Boreal Shield Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 19

This line graph shows annual indices of population change in birds of forest habitat for the Boreal Shield Ecozone+, based on data from the Breeding Bird Survey from 1968 to 2006. The abundance index shows a relative stable population for the period, ranging between approximately 160 and 230.

 

Table 23. Trends in abundance of selected species of forest birds that are characteristic of the Boreal Shield 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
Olive-sided Flycatcher-6.9%*1.461.180.460.18-87%
Boreal Chickadee-6.9%*0.580.260.090.09-85%
Canada Warbler-3.0%*2.271.691.441.00-56%
Evening Grosbeak-2.9%*5.498.054.411.64-70%
Purple Finch-2.9%*2.832.901.621.34-53%
Tennessee Warbler-2.3% 4.938.495.431.87-62%
Rose-breasted Grosbeak-2.1%*6.065.333.432.82-53%
Ruby-crowned Kinglet-1.8%*7.685.666.263.57-54%
Least Flycatcher-1.7%*10.099.007.035.80-43%
Veery-1.2%n18.4917.3914.1211.94-35%
Ruffed Grouse-1.1% 0.720.600.530.33-53%
Bay-breasted Warbler-0.8% 0.951.290.990.49-48%
Gray Jay-0.6% 1.461.381.211.13-23%
Ovenbird-0.5% 24.2124.1222.3420.16-17%
Swainson's Thrush-0.5% 15.3515.6513.7612.79-17%
American Redstart0.3% 5.956.156.775.991%
Yellow-rumped Warbler0.3% 6.307.826.715.90-6%
Cape May Warbler0.6% 0.571.351.090.53-6%
Black-and-white Warbler0.7% 3.855.065.123.840%
Red-eyed Vireo0.8%*32.5834.9737.7538.4018%
Philadelphia Vireo1.2% 0.771.011.280.9626%
Black-throated Green Warbler1.3% 1.812.252.652.8055%
Magnolia Warbler1.4%n6.407.419.029.2745%
Blackburnian Warbler1.8%*1.962.543.162.5028%
Blue-headed Vireo2.0%*1.341.381.511.9042%
Hairy Woodpecker2.6%*0.780.991.041.2763%
Winter Wren2.6%*5.255.5810.269.9790%
Broad-winged Hawk2.7% 0.210.500.300.56163%
Black-throated Blue Warbler3.0%n0.641.091.391.1275%

Table 23 - 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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Table 24. Change in detection of characteristic species of forest birds from surveys in 1981-1985 compared to 2001-2005 surveys from the Ontario Breeding Bird Atlas.Footnote1
SpeciesSouthern ShieldNorthern Shield
Cape May Warbler-35%*-1%
Olive-sided Flycatcher-35%*-11%
Tennessee Warbler-27%*3%
Ruby-crowned Kinglet-22%*18%*
Bay-breasted Warbler-17%*22%*
Rose-breasted Grosbeak-12%*-10%
Evening Grosbeak-10%*-26%*
Canada Warbler-10%*-17%
Purple Finch-6%*-19%*
Least Flycatcher-3%6%
American Redstart-1%24%*
Swainson's Thrush0%8%*
Veery0%22%*
Broad-winged Hawk2%16%
Red-eyed Vireo2%*15%*
Ovenbird2%*7%*
Black-and-white Warbler2%28%*
Gray Jay3%18%*
Ruffed Grouse4%27%*
Yellow-rumped Warbler4%*8%*
Blackburnian Warbler6%*35%*
Hairy Woodpecker9%*16%*
Magnolia Warbler13%*28%*
Boreal Chickadee18%6%
Black-throated Green Warbler18%*23%*
Black-throated Blue Warbler19%*93%*
Winter Wren21%*23%*
Philadelphia Vireo29%*21%
Blue-headed Vireo94%*72%*

Table 24 - Footnotes

Footnote 1

In this table: P is the statistical significance: * indicates statistically different from no change at P < 0.1. Species are sorted by magnitude of change in Southern Sheild region

Return to table 24 footnote1referrer

Source: adapted from Cadman et al. (2007)

The reasons for population changes are diverse. Several of these species exhibit substantial natural population fluctuations due to changes in seed supply (for example, Purple Finch), fire, and insect infestations, particularly those in more northern coniferous forests. The spruce budworm cycle plays a large role in the populations of several budworm specialists (Tennessee Warbler, Cape May Warbler, and Bay-breasted Warbler) (Palmer, 1965; Alley, 1984; Williams, 1996; Rimmer and McFarland, 1998; Baltz and Latta, 1998) and influences populations of many other insectivorous birds. These species respond positively to budworm outbreaks but may be negatively affected by aerial spraying to control spruce budworm. Global climate change may also affect birds. For example, declines in Gray Jay in Algonquin Park have been attributed, at least in part, to the rise in winter temperature that has caused this resident species’ winter food stores to spoil (Waite and Strickland, 2006). The marked decline of the Olive-sided Flycatcher, assessed as Threatened (COSEWIC, 2007d), is consistent with declines in many other aerial insectivores. As a neotropical migrant, it is also likely influenced by threats along migration routes and in its tropical wintering grounds, as are other species such as Rose-breasted Grosbeak, Canada Warbler, Cape May Warbler, Tennessee Warbler, and Bay-breasted Warbler. Similarly, population changes in short-distance migrant forest birds (such as, Winter Wren, Blue-headed Vireo, and Ruby-crowned Kinglet) are also influenced by conditions on their migration routes and wintering grounds. The Boreal Chickadee is endemic to the spruce-fir forests of the boreal region. Its trend has been very negative according to BBS results in both the Boreal Shield and Canada-wide between 1970 and 2006, as well as in results from the CBC (Butcher and Niven, 2007). However, no decline was found in the two decades between the Ontario breeding bird atlases (McLaren, 2007) which covered Ontario's boreal forest more comprehensively than the BBS.

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Shrub/early successional bird assemblage

Birds in early successional habitat such as old fields and regenerating forests show an overall small decline in population (Figure 20). Four species have experienced significant declines, consistent with their national trend (Table 25). The White-throated Sparrow trend is stable or slightly negative in this region (-0.6% per year) according to BBS data. Interestingly, data from the Christmas Bird Count show a decline in the south of its winter range and an increase in the north, suggesting a northward shift in its wintering distribution (Niven et al., 2004).

Figure 20. Annual indices of population change in birds of shrub/successional habitat for the Boreal Shield Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 20

This line graph shows annual indices of population change in birds of shrub/successional habitat for the Boreal Shield Ecozone+, based on data from the Breeding Bird Survey. The abundance index shows an overall small decline during the period, from approximately 180 to 140.

 

Table 25. Trends in abundance of selected species of shrub/successional birds that are characteristic of the Boreal Shield 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-3.3%*1.280.950.530.46-64%
Song Sparrow-1.7%*19.4812.8413.0411.43-41%
Mourning Warbler-1.3%*12.0611.748.928.30-31%
American Goldfinch-1.3%n6.315.624.855.21-17%
Gray Catbird-1.2% 0.990.900.790.69-31%
Yellow Warbler-1.0% 5.305.934.243.55-33%
Chestnut-sided Warbler-0.6% 18.2316.1415.1813.83-24%
White-throated Sparrow-0.6% 50.4042.4843.6442.15-16%
Nashville Warbler0.0% 17.1516.5617.8314.99-13%
Alder Flycatcher0.2% 8.489.228.969.107%
Lincoln's Sparrow0.2% 2.142.422.571.94-9%
Indigo Bunting1.9% 1.011.171.181.6362%

Table 25 - 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 25 footnote1referrer

 

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Other open habitat bird assemblage

Birds in the other open habitat assemblage show the largest overall decline of all assemblages in the Boreal Shield Ecozone+, with declines mainly apparent since the late 1980s (Figure 21, Table 22). Nevertheless, many of these species are not naturally characteristic of the region. Land clearing for agriculture created habitat in this area with a resultant increase in bird populations. Recent declines may be a reflection of the loss of this habitat through reforestation of abandoned farmland in some parts of this ecozone+ (Crins et al., 2007). Declines in the swallows and Common Nighthawk are consistent with a general decline in aerial insectivores across Canada (Table 26). Eastern Bluebirds have never been common in this ecozone+ though their small population appears to be faring well.

Figure 21. Annual indices of population change in birds of other open habitats for the Boreal Shield Ecozone+, based on data from the Breeding Bird Survey.

graph

Long Description for Figure 21

This line graph shows annual indices of population change in birds of other open habitats for the Boreal Shield Ecozone+, based on data from the Breeding Bird Survey from 1968 to 2006. The abundance index shows an increasing trend through to the 1970s, however the overall declining trend is predominant from 1978 to 2006 (approximately 54 and 9 respectively).

 

Table 26. Trends in abundance for selected species of birds of other open habitats that are characteristic of the Boreal Shield 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 Habitats
Population
Trend (%/yr)
 P1970s
(BBS)
1980s
(BBS)
1990s
(BBS)
2000s
(BBS)
Change
Bank Swallow-14.0%*6.504.590.490.10-98%
Brown-headed Cowbird-7.9%*7.533.881.640.58-92%
Common Nighthawk-6.4%*0.290.290.110.04-85%
Cliff Swallow-6.0%*7.3810.623.040.87-88%
Barn Swallow-5.3%*11.269.944.562.08-82%
Tree Swallow-3.3%*9.288.665.772.81-70%
American Kestrel-1.8%*1.011.020.760.56-44%
Eastern Kingbird-1.4% 1.922.551.441.01-47%
Eastern Bluebird3.8%*0.180.260.430.3492%

Table 26 - 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 26 footnote1referrer

 

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