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Transcript
Canada Warbler (Cardellina canadensis)
Breeding Bird Census
Habitat Data Analysis (1937-1991)
Veronica Aponte
Migratory Birds Conservation Section
Canadian Wildlife Service
Environment Canada
May 2014
Introduction
Biology:
Much of the biology of Canada Warblers (Cardellina canadensis) remains unknown. Basic research on their
breeding ecology, adult and brood survival rates, site fidelity, demographic regional variations and migration
populations is needed. In general, they have been found to prefer forests with high shrub densities, semiopen canopies caused by natural disturbances or forest harvesting, structurally complex floors and a dense
understory. The average size of a Canada Warbler territory during
the breeding season is between 0.4 and 2 ha depending on the study
site (COSEWIC 2008). They nest mostly in dense ferns, moss
hummocks or fallen logs and will lay one clutch of about 4-5 eggs per
season. The incubation period lasts for about 12 days and the female
mainly stays at the nest. Both parents will feed the young, which
fledge at around 8-10 days. Where cowbirds (Molothrus spp.) are
present, they will often parasitize the nest of Canada Warblers. More
than 80% of the species’ breeding range occurs within Canada; the
rest of the breeding population is found in the eastern United States.
Canada Warblers arrive on their breeding grounds in May and they
begin migrating back south as early as July (Michel et al. 2005; Figure
1). They are monogamous during the breeding season and pairs have
been observed migrating together and feeding in flocks of mixed
species.
This species has often been called the Canadian Flycatcher or
Canadian Flycatching Warbler for its ability to catch flying insects in
the air, known as flycatching. It also gleans, and even hover-gleans,
from foliage and the ground, feeds on spiders in the shrub layer, and Figure 1. Map of the breeding and wintering range
of the Canada Warbler (Cardellina canadensis).
eats fruit seasonally. It has also been found to take advantage of
Source: Boreal Songbird Initiative.
Spruce Budworm (Choristoneura fumiferana) outbreaks (Crawford
and Jennings 1989).
Population status:
Assessed in 2008, the Canada Warbler was listed as Threatened under the Species at Risk Act (SARA) in April
2008. In Canada, there are an estimated 1.2 to 2.7 million breeding adult Canada Warblers. They have been
declining by 2.9% every year between 1970 and 2012, but this decline lessened slightly between 2002 and
2012, averaging 1.95%. However, this trend varies greatly among provinces. The provinces in which the
greatest recent (2002-2012) decline has occurred are Nova Scotia and Prince Edward Island (Bird
Conservation Region 14), where they have declined by 8.64% (Environment Canada 2014).
Population trends vary depending on the period of time and the region under study. In eastern regions
where extensive habitat modification has occurred, declines in their density have followed initial
disturbances that alter the shrub layer and are caused by large-scale forest logging or fires, habitat
fragmentation and habitat destruction. However, the species seems to take advantage of disturbed areas if
the forest understory is given the opportunity to regenerate.
Exact reasons for the species’ decline are unknown; however, threats to the Canada Warbler include habitat
loss (especially wetland loss), forest fragmentation and forest age-class conversion on their breeding and
2
wintering grounds, as well as declines in insect abundance. In regions which have undergone habitat
conversion to agricultural lands, White-tailed Deer (Odocoileus virginianus) have expanded, and grazing of
the shrub layer by ungulates has been hypothesized to further contribute to the effects of habitat loss on the
Canada Warbler. In the Andes, approximately 90% of the forest has been cleared for agricultural or fuel
wood (Henderson et al. 1991). Furthermore, a decline in insect outbreaks, particularly of Spruce Budworm
(Choristoneura spp.), may also be affecting the Canada Warbler population. Although it is not a Spruce
Budworm specialist, during outbreaks it takes advantage of this food source and its population densities
tend to increase in those areas (Crawford and Jennings 1989).
Breeding Bird Census:
The Breeding Bird Census (BBC) was one of the oldest bird surveys in North America. It was conducted by
volunteers at a variety of locations, such as parks, nature preserves, wildlife refuges and on privately-owned
land. In this survey, the density of territorial males was estimated on a plot of homogeneous habitat usually
no larger than 10 ha in size. The census technique involved “spot-mapping” or “territory mapping” by
creating maps of the location of all singing males present in a census plot, and then identifying breeding pair
territories. Most of the survey plots were clustered near greater human population densities, namely in
eastern North America, but some extended to southern Yukon (Appendix B - Figure 1). The BBC provides
useful information on: population variations of a species within a site over time, changes that accompany
forest succession, and geographic variations in species composition. The data may also be used to identify
habitat requirements for a species in a region, which could improve our understanding of the biology of the
species. The Canadian Breeding Bird Census Database contains the records for all BBC surveys carried out in
Canada between 1929 and 1993. All territories and provinces are represented, except Prince Edward Island.
Probably the most important feature of the BBC is the habitat information associated with each of the
census plots. Vegetation species composition and prevalence information was recorded. From this, a habitat
classification scheme was created which includes five broad categories: broad-leafed forest, conifer and
mixed forest, wetland, open land and urban areas. These categories encompass vegetative structure
information, given the assumption that bird habitat choice is mainly based on vegetation structure. For a
detailed description of the Breeding Bird Census database, refer to Kennedy et al. (1999). For all BBC data
enquiries and requests please contact the Migratory Birds Conservation and Management group at
[email protected]
Methods
The latitude and longitude of each census plot was recorded and a primary, secondary and sometimes
tertiary habitat code was assigned (refer to Appendix A – Table 1 for a list of habitat codes). The density of
the species per 100 ha or square kilometer was calculated. The first, second and third most dominant canopy
species were identified for most plots, along with the primary and secondary dominant shrub species and
ground vegetation. The ecoregion in which the census plot was identified, the age of the stand, and the
presence or absence of water were noted. All plots in which Canada Warblers occurred are shown in
Appendix B - Figure 2. For more details on the variables measured during the BBC, refer to Kennedy et al.
(1999).
Species diversity was calculated using the compliment of the Simpson Diversity Index (1-D). A qualitative
data analysis was performed, in which the frequency distribution of the variables was used to create
contingency tables (or pivot tables in Microsoft Excel) and to determine occurrence and prevalence (defined
as the proportion of plots with a given habitat characteristic [i.e., habitat type] in which Canada Warblers
were found).
3
Results and Discussion
Avian species associations:
Canada Warblers occurred in a total of 84 plots (out of 640) in the years between 1937 and 1991. The
average bird species richness in these plots (S ± Standard Deviation, SD) was 23.9 (±7.9, range: 10-50) and
Simpson’s Diversity Index (1-D ± SD) was 0.90 (±0.05, range: 0.79-0.97). This is a high diversity index,
meaning that in habitats where Canada Warblers occurred, there were few common species but many rare
species. Where Canada Warblers were present, the White-throated Sparrow (Zonotrichia albicollis)
(prevalence: 81%), the Ovenbird (Seiurus aurocapilla) (76%), the Black-and-white Warbler (Mniotilta varia)
(73%), the Red-eyed Vireo (Vireo olivaceus) (71%) and the Nashville Warbler (Oreothlypis ruficapilla) (62%)
were the five most prevalent bird species. Except for the Ovenbird, all of these species tend to prefer forest
habitats with canopy openings. For all species except the Red-eyed Vireo, the nests are usually on or near
the ground (Kricher 1995; Cimprich et al. 2000; Falls and Kopachena 2010; Lowther and Williams 2011).
Similarly, Canada Warblers also tend to prefer forests with canopy openings and are ground nesters. It
appears that habitats that are suitable for those five species are similarly suitable for Canada Warblers.
However, in a study conducted in southern Saskatchewan, where the species was found almost exclusively in
pure aspen stands, the authors found that Canada Warblers were most likely to be found in the same forest
stand as Chestnut-sided Warblers (Setophaga pensylvanica), American Redstarts (Setophaga ruticilla),
Yellow Warblers (Setophaga petechial), Mourning Warblers (Geothlypis philadelphia), Least Flycatchers and
Brown-headed Cowbirds (Molothrus ater). To a lesser extent, they were associated with White-throated
Sparrows, Red-eyed Vireo and Ovenbirds (Hobson and Bayne 2000). Therefore, Canada Warbler species
associations appear to be region-dependent.
Habitat associations:
Table 1. Average density (per km2) of Canada Warblers (Cardellina canadensis) in census plots by habitat type during
the period between 1937 and 1991 (N=84).
Average Density
Density Range
Habitat type
Data Years
Occurrence
(per km2) ± SD
(per km2)
Conifer and mixed forest/woodland
23.40 ± 24.41
0.1-124
1937-1991
47
Broad-leafed/woodland
23.92 ± 19.66
0.1-100
1946-1982
30
Open land
41.12 ± 51.73
5.6-128
1978
5
Urban area
45.45
0-45.45
1983
1
Wetland
1.1
0-1.1
1968
1
The two main habitat types in which the Canada Warbler was found were conifer and mixed
forest/woodland and broad-leafed forest/woodland. Between 1937 and 1991 (N=23 sample years), they
occurred 47 times in conifer and mixed forest/woodland. Between 1946 and 1982 (N=17 sample years), they
occurred in broad-leafed forest/woodland 30 times. These results are consistent with previous studies which
have stated that “mixed forests appear to suit Canada Warblers better than hardwood or conifer stands, but
the species can be found in all three types” (Lambert and Faccio 2005). The species has also been found in
wetland (shrubby swamp) and in open land (3-7 year-old clear-cut) but much less often (Table 1). Although
in previous studies Canada Warblers have been found to be associated with wet forests such as floodplains
and swamps at 56 out of 84 sites (67%), no waterbodies were near plots at which Canada Warblers occurred.
They were most often found in mature or mid-age balsam fir habitats and mature poplar/paper
birch/willow/alder forests (Appendix A – Table 2). A total of 199 plots of conifer and mixed forest/woodland
were surveyed, of which 24% were found to have Canada Warbler; and 177 plots of broad-leafed
4
forest/woodland were surveyed, 17% of which had Canada Warbler. It would be interesting to explore the
BBC data within their breeding range for sites with habitat characteristics suitable for Canada Warblers but
where none were found. The data may or may not reveal specific habitat components which are lacking in
those areas devoid of Canada Warblers.
Table 2. Average density (per km2) ± standard deviation (SD) and prevalence of Canada Warblers (Cardellina
canadensis) in Breeding Bird Census plots (N=84) across a longitudinal gradient in Canada.
Longitude (west)
60-75
75-90
90-105
105-120
120-135
Average Density (per km2) ± SD
27.53 ± 31.22
24.57 ± 21.58
20.78 ± 13.57
8.00 ± 5.57
7.80
Occurrence
32
42
6
3
1
Prevalence
39.09%
50.00%
7.14%
3.57%
1.19%
The Canada Warbler occurred 42 times (out of 84 counts) between the 75th and 90th parallel of longitude
with an average density of 27.53 per km2 (± 31.22) and 32 times between the 60th and 75th parallel with an
average density of 24.46 (± 21.72; Table 2). Within the 60th and 75th parallel, there seems to be more
variability in the average density (per km2) of Canada Warblers compared to their average density between
the 75th and 90th parallel (Figure 2).
140
120
a
100
Average density (per km2)
80
60
40
20
0
103 111 112 121 122 123 200 201 212 221 222 223 224 231 232 253 314
140
120
b
100
80
60
40
20
0
104 111 112 113 114 121 200 201 211 213 221 222 231 232 243 442 500
Habitat Code
Figure 2. Average density of Canada Warblers (Cardellina canadensis) and standard deviation (there is no SD for regions
that were only sampled once) between (a) the 60th and 75th parallel and (b) between the 75th and 90th parallel in each
primary habitat type (refer to Appendix A – Table 1 for habitat code descriptions).
5
There are 194 ecoregions in Canada and Canada Warblers were found in 23 of these ecoregions. They were
mainly found in the Boreal Forest, specifically, the Boreal Shield ecozone (Table 2). They were also
secondarily found in the Atlantic Maritimes and Mixedwood Plains ecozones. In eastern Canada, where
studies on this species are lacking, surveys and nest searches should first begin in the regions and habitats
where they most often occur: the Algonquin-Lake Nipissing, Abitibi Plains, Appalachians, St. Lawrence
Lowlands and the Manitoulin-Lake Simcoe ecoregions. In decreasing order, the top three primary and
secondary canopy tree species in the Canada Warbler plots were Paper Birch (Betula papyrifera), Balsam Fir
(Abies balsamea) and Trembling Aspen (Populus tremuloides) (Appendix A –Table 3). Paper Birch and
Trembling Aspen are both early successional tree species, whereas Balsam Fir is considered a late
successional tree, appearing only 30-50 years after a fire. However, Balsam Fir is often found in mixed rather
than in pure stands, and is most often associated with Paper Birch and Trembling Aspen (Uchityl 1991). Thus
these data are consistent with previous accounts stating that Canada Warblers are often found in mixed
forest stands.
Table 2. Ecozones and ecoregions where Canada Warblers (Cardellina canadensis) was found during the Breeding Bird
Census (N=84; 1937-1991).
Average Density
Ecozone
Ecoregion
Occurrence Prevalence
(per km2) ± SD
Boreal Shield
19.25 ± 10.02
34
40.48%
90 Lac Seul Upland
6.67
1
1.19%
92 Rainy River
10.00
1
1.19%
94 Lake Nipigon
18.05 ± 13.78
4
4.76%
96 Abitibi Plains
35.18 ± 36.12
10
11.90%
97 Lake Temiscaming Lowland
25.00
1
1.19%
98 Algonquin-Lake Nipissing
25.80 ± 14.88
15
17.86%
99 Southern Laurentians
14.07 ± 14.94
2
2.38%
Atlantic Maritimes
27.23 ± 41.30
21
25.00%
117 Appalachians
38.89 ± 28.16
9
10.71%
118 Northern New Brunswick Uplands
16.17 ± 5.41
2
2.38%
120 Saint John River Valley
1.10
1
1.19%
121 Southern New Brunswick Uplands
9.00 ± 5.66
2
2.38%
122 Maritime Lowlands
124.00
1
1.19%
123 Fundy Coast
3.55 ± 4.88
2
2.38%
124 Southwest Nova Scotia Uplands
0.10 ± 0
3
3.57%
126 Annapolis-Minas Lowlands
25.00
1
1.19%
Mixedwood Plains
19.13 ± 14.63
21
25.00%
132 St-Lawrence Lowlands
32.79 ± 30.45
9
10.71%
133 Frontenac Axis
0.10
1
1.19%
134 Manitoulin-Lake Simcoe
15.53 ± 7.12
9
10.71%
135 Lake Erie Lowland
28.10 ± 24.54
2
2.38%
Boreal Plains
18.11 ± 6.74
7
8.33%
136 Slave River Lowland
10.50 ± 4.95
2
2.38%
147 Mid-Boreal Uplands
20.50 ± 24.75
2
2.38%
155 Interlake Plain
23.33 ± 12.01
3
3.57%
Taiga Plains
64 Hay River Lowland
7.80
1
1.19%
In 1978, a plot with varying age (post-logging) in a boreal mixedwood upland region (ecoregion 98,
Algonquin-Lake Nipissing) in northern Ontario, about 105 km from Hearst, was visited at nine separate
locations: a 3-year, a 5-year, a 6-year, a 9-year, an 11-year, a 13-year, a 17-year, and a 24-year-old stand, as
well as an unharvested pristine stand. The greatest abundance of Canada Warblers was found in the stand
6
that was harvested 6 years prior to the census (Figure 3). This 6-year old stand was also particularly rich in
many other species (e.g., Chestnut-sided Warbler, Tennessee Warbler (Oreothlypis peregrina) and Mourning
Warbler). The surveyor of this census habitat stated that “the combination of a well-developed shrub and
young tree layer, abundant dead trees and a dense overstory resulted in a particularly rich bird population”
and “tree mortality caused by an earlier budworm outbreak and by cutting disturbance also resulted in
considerable blowdown which further opened the stand” (Van Velzen 1980). It is likely that these two
factors – the presence of a rich shrub layer and the earlier budworm outbreak – attracted the high density of
Canada Warblers, and other bird species, to this stand. Although these data are only for one sample year
and are not statistically valid, it is interesting to note that within just one forest region with multiple plots of
differing successional stages, differences in Canada Warbler densities were observed. These differences
correspond to the observations made in previous Canada Warbler breeding habitat studies. In their review
of studies on Canada Warblers, Lambert and Faccio (2005) found that in upland habitats, this species seems
to be a disturbance specialist, moving into regenerating forest patches following wind-throw, ice damage,
fire or timber harvest. They tend to be abundant in logged areas where residual trees have remained for 520 years following harvest.
Canada Warbler Density (per Km2)
140
120
100
80
60
40
20
0
3
5
6
9
11
13
17
24
250
Boreal Mixedwood Upland Cutover Stand Age
Figure 3. Canada Warbler (Cardellina canadensis) plot density for nine plots in a boreal mixed-wood stand in one region
in 1978 with varying cutover ages.
Conclusion
This report does not include statistical tests, but rather it summarizes the data gathered during the Breeding
Bird Census from 1937-1991 in a comprehensive and descriptive manner. The results from the BBC data
support previous studies done on Canada Warbler habitat preferences. This species inhabits both deciduous
and coniferous forests as well as mixed forests. In some regions, mainly in the eastern and southeastern
portion of its breeding range, it appears to prefer regenerating forests which have undergone some
disturbance (wind storm, fire or patch-cut) which create openings in the canopy. Habitat that is created from
partially-logged forests is transitory at the stand scale but could be sustained at the forest scale by rotating
harvests and taking into consideration lag time establishment response of Canada Warblers. Furthermore,
this species appears to prefer reduced canopy height and a dense shrub and fern layer because these habitat
attributes provide foraging areas, conceal nests and expose song perches for males. In contrast, in more
western regions of its breeding range, this warbler is more abundant in late-successional undisturbed
forests. In summary, it would appear that Canada Warblers have a preference for different habitat types
depending on the geographic region being studied (eastern versus western Canada). The lag time associated
7
with Canada Warbler establishment in disturbed habitats appears to also vary geographically: it may take
longer in boreal mixedwood forests of western Canada. Future ecological studies on Canada Warblers,
especially regarding their breeding success and minimum forest cut size needs where they occur, are
necessary in order to determine priority areas of critical habitat for this species. Information from the BBC
can be extremely valuable in that it can be used to narrow potential research locations with varying Canada
Warbler densities for future studies.
Acknowledgements
This report was prepared for Judith Kennedy, Bird Conservation Biologist, using data extracted from the
Canadian Breeding Bird Census Database by Ms. Kennedy.
8
References
COSEWIC. 2008. COSEWIC assessment and status report on the Canada Warbler Wilsonia Canadensis in Canada. Committee
on the Status of Endangered Wildlife in Canada. Ottawa. vi + 35 pp.
Cimprich, D.A., Moore F.R. and Guilfoyle, M.P. 2000. Red-eyed Vireo (Vireo olivaceus), The Birds of North America Online (A.
Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:
http://bna.birds.cornell.edu/bna/species/527.
Crawford, H.S., and Jennings, D.T. 1989. Predation by birds on spruce budworm Chorisoneura fumiferana: functional,
numerical and total responses. Ecology, 70: 152-163.
Environment Canada, 2014. North American Breeding Bird Survey - Canadian Trends Website, Data-version 2012.
Environment Canada, Gatineau, Quebec, K1A 0H3. http://www.ec.gc.ca/ron-bbs/P002/A001/?lang=e
Falls, J.B., and Kopachena, J.G. 2010. White-throated Sparrow (Zonotrichia albicollis), The Birds of North America Online (A.
Poole Ed.). Ithica: Cornell Lab of Ornithology; retrieved from the Birds of North America Online:
http://bna.birds.cornell.edu/bna/species/128.
Henderson, A., S.P. Churchill, and J.L. Luteyn. 1991. Neotropical plant diversity. Nature 351: 21-22.
Hobson, K.A. and Bayne, E. 2000. Breeding bird communities in Boreal forest of Western Canada consequences of “unmixing”
in mixedwoods. The Condor, 102(4): 759-769.
Kennedy, J.A., Pam Dilworth-Christie and A.J. Erskine. 1999. The Canadian Breeding Bird (Mapping) Census Database.
Technical Report Series No. 342. Canadian Wildlife Service, Ottawa, Ontario. http://publications.gc.ca/site/archiveearchived.html?url=http://publications.gc.ca/collections/Collection/CW69-5-342E.pdf
Kricher, J.C. 1995. Black-and-white Warbler (Mniotilta varia), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell
Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/158.
Lambert, J.D. and Faccio, S.D. 2005. Canada Warbler population status, habitat use, and stewardship guidelines for
northeastern forests. VINS Technical Report 05-4.
Lowther, P.E. and Williams, J.M. 2011. Nashville Warbler (Oreothlypis ruficapilla), The Birds of North America Online (A. Poole,
Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:
http://bna.birds.cornell.edu/bna/species/205.
Michel, N., D.F. DeSante, D.R. Kaschube, and M.P. Nott. 2005. The Monitoring Avian Productivity and Survivorship (MAPS)
Program Annual Reports, 1989-2001. NBII/MAPS Avian Demographics Query Interface.
http://www.birdpop.org/nbii/NBIIHome.asp (February 2005).
Schieck, J. and Nietfeld, M. 1995. Bird species richness and abundance in relation to stand age structure in aspen mixedwood
forests in Alberta, in Relationships between stand age, stand structure, and biodiversity in aspen mixedwood forests in
Alberta (J.B. Stelfox, ed.). Alberta Environmental Centre, Vegreville, AB, and Canadian Forest Service, Edmonton, AB.
Uchityl, R.J. 1991. Abies balsamea. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest
Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available:
http://www.fs.fed.us/database/feis/ (May 2014).
Van Velzen, W.T. 1980. “176. Boreal mixedwood-6-year-old upland cutover” (p. 91) in: Forty-third Breeding Bird Census.
American Birds 34(1): 41-106.
9
Appendix A – Tables
Table 1. Habitat codes associated with primary habitat types.
Primary Habitat
Broad-leafed forest/woodland
Indeterminate
Mature
Young
Disturbed
Poplar/Paper Birch/Willow/Alder
Mature
Mid-Age
Young
Disturbed
Maple/Beech/American Elm
Mature
Mid-Age
Young
Silver Maple/American Elm
Mature
Red Oak/Other Eastern Oak
Mature
Mid-Age
Disturbed
Bur Oak/Green Ash/ Manitoba Maple
Mature
Mid-Age
Code
101
103
104
111
112
113
114
121
122
123
131
140
141
142
144
151
152
Wetlands
Shallow Fresh Marsh
Shrubby Swamp
Swamp Forest
Fen
Wet Bog
Dry Bog
Riparian Sand and Gravel
Riparian shrubbery
313
314
315
321
322
323
331
332
Open Land
Arctic Tundra “desert”
Arctic Tundra “oasis”
Alpine Tundra
Tundra/forest shrubland
Short-grass prairie
Long-grass prairie
Prairie Grassland (unmowed)
Prairie Grassland
Prairie/forest shrubland
Cropland
Fallow
Hay field or Pasture
Old field
Clear-cuts 1-2y after cutting
Clear-cuts 3-7y – natural
Clear-cuts 3-7y – planted
411
412
413
414
421
422
423
424
425
431
432
433
434
441
442
443
Primary Habitat
Conifer and mixed forest/woodland
Indeterminate
Mature
Mid-Age
Black/White/Red Spruce
Mature
Mid-Age
Young
Disturbed
Balsam Fir
Mature
Mid-Age
Young
Disturbed
Eastern Hemlock/Cedar/Pine
Mature
Mid-Age
Young
Tamarack/Black Spruce
Mature
Mid-Age
Young
Jack Pine/Lodgepole Pine
Mature
Mid-Age
Young
Douglas-Fir/Lodgepole Pine
Mature
Young
Disturbed
Englemann Spruce/Subalpine Fir
Mature
Mid-Age
Young
Disturbed
Urban Area
Urban*
Urban park
Urban built-up
Urban “desert”
Code
200
201
201
211
212
213
214
221
222
223
224
231
232
233
241
242
243
251
252
253
261
263
264
281
282
283
284
500
510
520
530
*A habitat code for “Urban” was not included in the original list
but was added here as 500, for the purposes of this report.
10
Table 2. Frequency of occurrence and prevalence of the Canada Warbler (Cardellina canadensis) out of 84
census plot counts of different stand ages.
Broad-leafed/woodland
Mature
Mid-age
Young
Disturbed
Poplar/Paper Birch/Willow/Alder2
Mature
Frequency of occurrence
(out of 84 total counts)
30
16
9
3
2
19
11
Conifer and mixed forest/woodland
Mature
Mid-age
Young
Disturbed
Balsam Fir2
Mature
Mid-age
473
16
18
10
1
20
8
12
56%
19%
21%
12%
1%
24%
10%
14%
Open Land (3-7 years after cutting)
Wetlands
Urban Area
5
1
1
6%
1%
1%
All Habitats4
Mature
Mid-age
Young
Disturbed
32
32
13
3
38%
38%
15%
4%
Primary Habitat1
Prevalence
36%
19%
11%
4%
2%
23%
13%
1. Five possible primary broad habitats were identified (broad-leafed forest/woodland, wetlands, open land, conifer
and mixed/woodland and urban area).Within each of these, there were subcategories of habitats.
2. Within the broad-leafed/woodland broad habitat category, Canada Warblers were mostly found in poplar/paper
birch/willow/alder habitat types (habitat code: 111-114) and within the Conifer and mixed forest/woodland, they
were primarily found in Balsam Fir habitats (habitat code: 221-224).
3. The sum of mature, mid-age, young and disturbed do not equal 47 because two of sites were assigned the habitat
code of 200 which is not age-defined.
4. The sum of counts for all habitats by age does not equate to 84 but to 80 because some of the habitat codes are
not age-defined.
11
Table 3. Average density (per km2) of Canada Warblers (Cardellina canadensis) in a census plot with a
particular dominant canopy species. Occurrence refers to the number of time the canopy tree species was
the primary canopy species in plots at which Canada Warblers occurred.
Average Density
(per km2) ± SD
Occurrence as Primary Tree Species
(out of 65*)
Prevalence
Paper Birch
25.83 ± 24.84
17
26.15%
Balsam Fir
34.38 ± 37.42
14
21.53%
Trembling Aspen
17.94 ± 14.07
9
13.85%
Tamarack
16.47 ± 5.68
6
9.23%
Eastern Hemlock
21.78 ± 22.12
4
6.15%
Sugar Maple
12.33 ± 3.21
3
4.61%
Black Spruce
10.70 ± 16.74
3
4.61%
Eastern White Pine
12.33 ± 3.21
3
4.61%
Yellow Birch
25.00
1
1.54%
American Beech
25.00
1
1.54%
Spruce spp.
0.10
1
1.54%
Balsam Poplar
11.00
1
1.54%
Pin Cherry
50.00
1
1.54%
Canopy Species
Eastern White Cedar
124.00
1
*Only 65 of the 84 Canada Warblers plots had identified canopy species.
1.54%
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Appendix B – Figures
Figure 1. Map of the Breeding Bird Census plot locations in Canada.
Figure 2. Map of the Breeding Bird Census plot locations in Canada in which Canada Warblers (Cardellina canadensis) occurred.
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