Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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% 12 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. 14