B.C. Ministry of Environment, Lands and Parks, Wildlife Branch, 780 Blanshard ... Habitat use in British Columbia also includes edges along mature deciduous ...
STATUS OF THE CANADA WARBLER IN BRITISH COLUMBIA
by J. M. Cooper K. A. Enns M. G. Shepard
Wildlife Working Report No. WR-81
February 1997 xi
British Columbia, Canada’s most westerly province, has a bounty of biological diversity. British Columbia’s snowclad peaks, rain-drenched forests, arid grasslands, all sizes of rivers, lakes, and wetlands, and a long and rugged coast provide habitats for more species of living organisms than are found anywhere else in Canada. However, this very diversity means that there is much to be discovered about these organisms — their distribution, abundance, habitat requirements, and interrelationships with their environment. Increasing our knowledge of this biodiversity will help us with the complex task of sustainably managing our land and waters. In 1992, the Provincial Government initiated a co-operative biodiversity research program with funding from the Corporate Resource Inventory Initiative, the British Columbia Ministries of Forests (Research Branch), Environment, Lands, and Parks (Wildlife and Habitat Protection Branches), and Tourism and Culture (Royal B.C. Museum); and the Forest Resource Development Agreement (FRDA II). In 1996, funding from Forest Renewal BC (FRBC) was received for a biodiversity research extension proposal. One goal of the original research program, and more recently the FRBC extension project, is to extend information to scientists, resource managers, and the public through biodiversity publications. These publications are intended to increase awareness and understanding of biodiversity, promote the concepts and importance of conserving biodiversity, and communicate provincial government initiatives related to biodiversity. We hope that they will be used as tools for the conservation of British Columbia’s rich, living legacy.
For more information contact: B.C. Ministry of Environment, Lands and Parks, Wildlife Branch, 780 Blanshard St., Victoria, BC V8V 1X4 or B.C. Ministry of Forests, Research Branch, 31 Bastion Square, Victoria, BC V8W 3E7 or Royal B.C. Museum, P.O. Box 9815, Stn Prov Govt, Victoria, B.C. V8W 9W2
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STATUS OF THE CANADA WARBLER IN BRITISH COLUMBIA
by J. M. Cooper K. A. Enns M. G. Shepard
Ministry of Environment, Lands and Parks Wildlife Branch Victoria, BC
Wildlife Working Report WR-81 February 1997 i
“Wildlife Working Reports frequently contain preliminary data, so conclusions based on these may be subject to change. Working Reports receive little review. They may be cited in publications, but their manuscript status should be noted. Copies may be obtained, depending upon supply, from the Ministry of Environment, Lands and Parks, Wildlife Branch, 780 Blanshard Street, Victoria, BC V8V 1X4.”
Canadian Cataloquing in Publication Data Cooper, John M. (John Morton) , 1956Status of the Canada Warbler in British Columbia (Wildlife working report ; no. WR-81) Includes bibliographical references ISBN 0-7726-2997-8 1. Canada Warbler - British Columbia. I. Enns, K. A. (Katherine A.) II. Shepard, Michael G., 1951III. BC Environment. Wildlife Branch. IV. Title. V. Series QL696.P2438C664 1996 598.8'72
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C96-960275-8
FOREWORD In cases where a Wildlife Working Report or Bulletin is also a species status report, it may contain a status recommended by the author for the species. This recommended status is the opinion of the author and may not necessarily reflect that of the Wildlife Branch. Official status designation will be made by the Wildlife Branch in consultation with experts, and the data contained in the status report will be considered during the evaluation process.
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ABSTRACT The Canada Warbler (Wilsonia canadensis) is an uncommon, neotropical migrant, forest songbird that is locally distributed in the Boreal Plains and Taiga Plains ecoprovinces of northeastern British Columbia. Its habitat is deciduous forest (trembling aspen and birches) and deciduous-dominated mixedwoods with rich shrub and ground layers, often with considerable amounts of natural disturbance and uneven canopy layers. Habitat use in British Columbia also includes edges along mature deciduous stands, a habitat not generally reported in other regions. Very few data exist on populations in British Columbia, and those that do exist are small and localized in area. There are two short-term threats to populations: (1) logging of aspen forests for pulpwood and brush control, and (2) increased exposure to cowbird parasitism and predation through general fragmentation of habitat. However, logged blocks may regenerate to a suitable stage more rapidly than for other warbler species of concern. Much of its habitat is on wet, unstable, steep slopes that will be left unharvested because of slope instability. The Canada Warbler should remain on the Blue List because of lack of data on ecology, distribution, population sizes, and uncertainties around the effect of logging on habitat quality over the long term.
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ACKNOWLEDGEMENTS This project was managed and funded by the Ministry of Environment, Lands and Parks, and production of the final report was made possible by the financial support of the Wildlife Branch, B.C. Ministry of Environment and Forest Renewal British Columbia (FRBC). Myke Chutter and Syd Cannings provided comprehensive and constructive reviews of earlier drafts of this manuscript. Ted Lea provided an extensive review of the section on habitat in an earlier draft. Jim Schieck sent us his unpublished manuscript on warbler habitat use in Alberta, which provided useful context. Rhonda Millikin gave us her thoughts on the relative status of, and our provincial management responsibilities for, the Canada Warbler. Art Lance generously provided us with reports and unpublished information from his study near Dawson Creek. Eric Lofroth and Laura Darling gave us useful information from their respective studies in the northeast. Wayne Campbell commented on the status designation and provided access to some literature. Mike Vislai, Richard Kabzems, Dave Parminter, Frank McAllister, Brian Churchill, Andrew Harcombe, John Parminter, Bob Ferguson, Ken Bolan, Everett Peterson, Merle Peterson, Nicola Parfitt, and Colin Woods all provided considerable help with the habitat section. We thank them all for their generous help and Myke, especially, for his encouragement. English and copy editing of this document were done by Ted Wagstaff, and final figures and typesetting were done by Gail Harcombe.
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TABLE OF CONTENTS 1.0 INTRODUCTION .................................................................................................................................... 1 2.0 DISTRIBUTION ...................................................................................................................................... 1 2.1 Global .............................................................................................................................................. 1 2.2 British Columbia .............................................................................................................................. 1 3.0 POPULATION SIZE AND TRENDS ..................................................................................................... 2 3.1 Population Size ................................................................................................................................ 2 3.2 Population Trends ............................................................................................................................ 4 4.0 GENERAL BIOLOGY ............................................................................................................................ 4 4.1 Reproductive Capability .................................................................................................................. 4 4.2 Species Movement ........................................................................................................................... 5 4.3 Behaviour/Adaptability .................................................................................................................... 5 4.3.1 Tolerance to human disturbance ......................................................................................... 5 4.3.2 Food ...................................................................................................................................... 5 4.3.3 Response to sudden environmental change ........................................................................ 6 4.3.4 Causes of mortality .............................................................................................................. 6 4.3.5 Protection of areas of concentration ................................................................................... 6 5.0 HABITAT .............................................................................................................................................. 6 5.1 Description of Habitats .................................................................................................................... 6 5.2 Nest Site Specialization ................................................................................................................... 7 5.3 Distribution of Habitat ..................................................................................................................... 7 5.3.3 Biogeoclimatic Zones (BGZ) .............................................................................................. 7 5.3.2 Ecoregions ............................................................................................................................ 8 5.3.3 Broad Habitat Classes (BHC) ............................................................................................. 8 5.4 Present Habitat Availability ............................................................................................................. 8 5.5 Trends in Quantity and Quality of Critical Habitat by Time ........................................................ 8 5.6 Rate of Habitat Change .................................................................................................................. 10 5.7 Legal Status of Habitat ................................................................................................................... 10 5.7.1 Timber Supply Areas (TSA) .............................................................................................. 10 5.7.2 Protected areas .................................................................................................................... 11 5.8 Can Critical Habitat be Protected by Means Other Than Acquisition? ...................................... 12 6.0 LEGAL PROTECTION .......................................................................................................................... 12 7.0 LIMITING FACTORS ............................................................................................................................ 12 7.1 Breeding Habitat ............................................................................................................................. 12 7.2 Silviculture ...................................................................................................................................... 13 7.3 Degree of Habitat Specialization ................................................................................................... 13 7.4 Brown-headed Cowbird Parasitism ................................................................................................ 14 7.5 Predation .......................................................................................................................................... 14 7.6 Grazing ............................................................................................................................................ 14 7.7 Agriculture ...................................................................................................................................... 14 7.8 Urban Development ........................................................................................................................ 14 7.9 Prescribed Fire ................................................................................................................................ 14 7.10 Air Pollution .................................................................................................................................... 15 7.11 Seismic Lines and Roads ............................................................................................................... 15 7.12 Winter Habitat ................................................................................................................................. 15
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8.0 SPECIAL SIGNIFICANCE OF THE SPECIES ................................................................................... 16 8.1 Status ............................................................................................................................................. 16 8.2 Degree of Public Interest ................................................................................................................ 16 8.3 Related Species ............................................................................................................................... 16 9.0 RECOMMENDATIONS AND MANAGEMENT OPTIONS ............................................................... 16 10.0 RESEARCH REQUIREMENTS ............................................................................................................ 17 11.0 EVALUATION ......................................................................................................................................... 17 12.0 LITERATURE CITED ............................................................................................................................ 18
LIST OF TABLES Table 1. Broad Habitat Classes (BHCs) used by the Canada Warbler .......................................................... 9 Table 2. Comparison of six rare songbirds restricted to northeastern British Columbia ............................ 18
LIST OF FIGURES Figure 1. Breeding and wintering distribution of the Canada Warbler .......................................................... 2 Figure 2. Locality records for the Canada Warbler in British Columbia ....................................................... 3 Figure 3. Timber Supply Areas in northeastern British Columbia .................................................................11
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1.0 INTRODUCTION
2.0 DISTRIBUTION
The Canada Warbler (Wilsonia canadensis) is a long-distance, forest-dwelling, neotropical migrant that is restricted in British Columbia to the northeastern corner of the province. Populations are thought to be small and local. Because of its restricted distribution and small populations the Canada Warbler is listed on the B.C. Wildlife Branch Blue List as vulnerable (B.C. Wildlife Branch 1993).
2.1 Global The Canada Warbler breeds from northeastern British Columbia, across Canada east to Nova Scotia (Figure 1; Godfrey 1986); and in the eastern USA, in the Appalachians as far south as northern Georgia (American Ornithologists’ Union 1983). It winters primarily in South America from northern Colombia and Venezuela to eastern Peru and northern Brazil. A few winter as far north as southern Mexico (American Ornithologists’ Union 1983).
Recent studies have indicated a widespread decline in populations of neotropical migrant songbirds (those that breed in temperate regions and winter in tropical regions), and that these declines have accelerated for some species in recent years (Robbins et al. 1989b; Askins et al. 1990; Finch 1991; Hagan and Johnston 1992). Causes of these declines are diverse, but are widely thought to occur on breeding, wintering, or migrating areas, or a combination of the three (Sherry and Holmes 1993).
2.2 British Columbia The Canada Warbler is restricted to the Boreal Plains and Taiga Plains ecoprovinces in the northeast corner of British Columbia (Figure 2; Godfrey 1986; Enns and Siddle 1992). Most records are from along the Peace River from Hudson's Hope east to the Alberta border, and in the vicinity of Fort Nelson.
This report contains a synthesis of available information on Canada Warblers, including an overview of the species’ biology, habitat requirements, limiting factors, distribution, status, and prognosis for the future. Information was gathered from published and unpublished literature, personal records, and personal communications with biologists. Recommendations for management techniques that will help maintain populations in British Columbia and for additional research that is needed to manage the species in the future are presented.
The Canada Warbler reaches the northwestern extreme of its range in northern Alberta and northeastern British Columbia. It may be a recent arrival to British Columbia as the first record for the province was in 1974 (Erskine and Davidson 1976). Salt and Salt (1976) state that it breeds locally in northeastern and central Alberta, with an extralimital report coming from Grande Prairie, 75 km from the Alberta/British Columbia boundary. This suggests that the species was scarce or non-existent in northwestern Alberta, adjacent to British Columbia, as recently as the 1970s. However, it may have just been overlooked because of its local distribution and the lack of ornithologists in the Peace River region.
This report is one of six status reports on rare, northeastern songbirds commissioned by the B.C. Wildlife Branch during 1994, and is part of an ongoing program to more effectively manage species at risk for long-term viability. The other five species are Bay-breasted Warbler (Dendroica castanea), Black-throated Green Warbler (Dendroica virens), Cape May Warbler (Dendroica tigrina), Connecticut Warbler (Oporornis agilis), and Philadelphia Vireo (Vireo philadelphicus).
The Canada Warbler is probably more widely distributed than previously known because recent studies have documented significant range
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be one of the least abundant warblers in northeastern British Columbia; being the sixth least frequently recorded warbler (of 20 species; Siddle 1992). However, in a recent study of northeastern songbird habitat associations, where various habitat types were sampled from Pine Pass north to the Yukon border, Canada Warblers accounted for 9.3% of 332 rare songbird sightings and was the fifth most frequently recorded warbler (of nine species) restricted to the northeast (Enns and Siddle 1992). In addition, Lance and Phinney (1994) felt that it was fairly common in mixedwood forests southwest of Dawson Creek.
extensions: west along the Peace River to Hudson’s Hope and north to Maxhamish Lake (Enns and Siddle 1992). It is not known if these range extensions are the result of increased observer effort or real movements of populations.
3.0 POPULATION SIZE AND TRENDS 3.1 Population Size There are few data on population sizes in British Columbia. The Canada Warbler is considered to
Breeding Range Winter Range
Figure 1. Breeding and wintering distribution of the Canada Warbler. 2
Figure 2. Locality records for the Canada Warbler in British Columbia. 3
many details of breeding are completely lacking from anywhere in the range of this poorly known warbler. The following information is taken from studies in eastern North America.
The Canada Warbler has been found to be sparsely and locally distributed in northern Alberta during recent atlas surveys (Semenchuk 1992); our data indicate that it may be more locally abundant in this province.
Canada Warblers usually lay a clutch of 4 eggs, (range 3-5) (Bent 1953; Harrison 1978; Peck and James 1987). Egg-laying likely occurs in June in northeastern British Columbia. The incubation period is unknown, but is probably 11-13 days, as in the closely related Wilson’s Warbler (Wilsonia pusilla; Stewart et al. 1977).
3.2 Population Trends There are no data on population trends in British Columbia, although some authors believe that all northeastern warblers are in decline (e.g., Siddle 1992). However, given that the Canada Warbler has likely recently established itself in British Columbia, and new populations are being found, we feel that populations are probably stable or increasing rather than decreasing.
Nestlings are probably present from late June through mid-July. The nestling period is unknown but, again, is likely similar to the 10-11 days of the Wilson’s Warbler (Stewart et al. 1977; Harrison 1978). A single brood is raised each year in British Columbia, a widespread trend in warblers (Morse 1989). Double-brooding is rare in warblers, even in species nesting in the southern USA (Nolan 1978). There are no data on hatching success, survival of nestlings, or fledging success. No nests have been found in British Columbia, but young out of the nest have been found along Johnstone and Peace Island Park roads in Taylor, and in the forests around the Fort Nelson Airport (Siddle 1992).
Comprehensive analyses of breeding bird surveys have revealed stable short and long-term trends, generally, in eastern North America (Robbins et al. 1989b; Hagan et al. 1992). However, Canada Warblers were reported to be declining in local areas of eastern Canada where habitat was disappearing (Robbins et al. 1993) and in central New England, where they were declining significantly on breeding bird surveys at -5.3% annually (Witham and Hunter 1992). There are insufficient data to analyze breeding bird surveys in British Columbia (Erskine et al. 1992).
Numbers of young produced are limited by clutch size (3-5 eggs) and numbers of broods produced (1 brood). In general, the annual reproductive potential of most warblers is relatively low compared to many other small, short-distance migrant or resident songbirds (Morse 1989). The maximum life span reported is 7-8 years (Klimkiewicz et al. 1983).
It is important to consider that widespread population declines are difficult to detect because a given species might contract its range, occupy fewer habitats, decline in abundance, or a combination of the three, and there may be significant error in counting methods (Wilcove and Terborgh 1984). More long term research is required to determine trends in British Columbia.
Age/sex ratios of populations in British Columbia are unknown. However, most warbler populations are thought to have a surplus of males (Stewart and Aldrich 1952; Ficken and Ficken 1962; Proctor-Gray and Holmes 1981). Canada Warblers breed as one-year-olds, but some individual yearlings likely do not breed, as in some other warblers (Morse 1973).
4.0 GENERAL BIOLOGY 4.1 Reproductive Capability There are no data on the breeding ecology of Canada Warblers in British Columbia. Indeed,
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earlier than the mid-to-late August movement reported in central Alberta (Salt 1973; Salt and Salt 1976).
The Canada Warbler is thought to be monogamous, whereas the Wilson’s Warbler is occasionally polygynous (Ehrlich et al. 1988). Observations of seemingly paired Canada Warblers during early spring migration in Panama suggest that pairing takes place on the wintering grounds or during migration (Greenberg and Gradwohl 1980), an unusual strategy in northern warblers (Morse 1989); but an alternative view is that these “pairs” are one male and one female coexisting, rather than being “paired,” in mixedspecies winter flocks because of a lack of intersexual aggression (Terborgh 1989). Upon arriving on the breeding grounds, males select nesting territories and defend them from other conspecific males.
4.3 Behaviour/Adaptability 4.3.1 Tolerance to human disturbance Canada Warblers are not unduly sensitive to human disturbance except for activities that affect habitat integrity (logging, clearing) or prey base (pesticide spraying). On the wintering grounds, Canada Warblers tolerate some disturbance (i.e., partial clearing of forests) of their montane forest habitat (Terborgh 1989; Petit et al. 1993). Their response to some habitat alterations on the breeding grounds is not well known, however (see Limiting Factors). Large-scale spraying of insecticides would inevitably reduce their insect prey base. Application of herbicides to eliminate deciduous forest along roads would reduce shrubby habitat used for foraging by pairs frequenting roadsides.
There are no data on territory size, but territories are likely less than 2 ha. Densities in good habitat have been recorded at 56 territorial males/100 ha in northern Alberta (Francis and Lumbis 1979), 12-17 territorial males/km2 in New Brunswick and Ontario (Erskine 1977), and 60 territorial males/ 100 ha in a montane forest in New Hampshire (Sabo and Holmes 1983).
4.3.2 Food 4.2 Species Movement The Canada Warbler occupies one of the most restricted foraging niches (low shrubs and ground) of all North American warblers (Power 1971), even though it eats a wide variety of prey and has several foraging methods. It is insectivorous and eats a variety of small insect larvae, flies, moths, beetles, small wasps, leafhoppers, small locusts, spiders, snails, and eggs of spiders and insects (Knight in Bent 1953; Keast 1980). It feeds mainly by gleaning prey from foliage of saplings and shrubs, but also forages on the ground and is an active flycatcher (Bent 1953; Keast 1980; Sabo and Holmes 1983). It hawks aerial insect prey more often than most other warblers, and was previously known as the “Canada Flycatching Warbler” (Bent 1953). In British Columbia, most foraging is done within 3-4 m of the forest floor (Enns and Siddle 1992), and 2.6-5.2 m in Illinois (Sabo and Holmes 1983).
The Canada Warbler winters further south than most other North American warblers (similar to the Connecticut Warbler), so has a longer distance to travel during migration, and arrives in Canada (very late May and early June) later than all warblers except for Mourning and Blackpoll warblers (Keast 1980; Francis and Cooke 1986). Males migrate earlier than females, a general pattern in many bird species; in southern Ontario, mean date of arrival for males was three days earlier than for females (Francis and Cooke 1986). Spring migrants enter northeastern British Columbia beginning in the last few days of May, with most probably arriving in early June. Early arrivals in Alberta also appear in the last few days of May (Salt 1973; Salt and Salt 1976). After nesting is completed, the southward migration occurs from mid July through late August, 5
4.3.3 Response to sudden environmental change
forages mainly on the ground or in the shrub understorey. Habitat descriptions include: • Alberta — open, deciduous forest or near streams with brushy borders and open to the sun, or thick stands of willow and alder along streams and dense shrubs in swamps near the forest edge (Salt 1973); mesic deciduous or mixed woods, taller than 10 m with a rich deciduous shrub layer taller than 1.5 m on slopes >15o (Francis and Lumbis 1979); mature and old-growth aspen forest (J. Schieck, pers. comm.).
Few data are available. In general, late spells of cold, spring weather are known to cause mortality in early migrant warblers (Morse 1989). There are no data to suggest that populations expand and contract rapidly in response to changes in prey availability, as do Cape May and Bay-breasted warblers in response to spruce budworm outbreaks (Morse 1978).
4.3.4 Causes of mortality Specific data are lacking for this species, but predation and cowbird parasitism are known to be the two leading causes of nest mortality for neotropical migrants (Martin 1992). Migrating warblers suffer mortality from natural environmental effects and from human-related factors such as collision with light towers (e.g., Crawford 1978; Ralph 1981).
• Michigan — small forest openings with dense shrub and ground cover (Collins et al. 1982). • Ontario — mixedwood, deciduous, and coniferous forest with heavy undergrowth, often on slopes or in rocky areas (Peck and James 1987) • Nova Scotia — thick swamps within coniferous forest (Bent 1953).
4.3.5 Protection of areas of concentration
• New England — mixed forest especially in deep ravines, along streams, and in tangled maple swamps (Griscom and Sprunt 1957).
This warbler is sparsely but widely distributed on the breeding and wintering grounds, and small numbers are undoubtedly protected in various reserves/parks in both regions. The status of populations in protected areas in British Columbia is unknown, however.
In northeastern British Columbia, Canada Warblers were found most often in: • dense subcanopy of mature poplar stands near Fort Nelson (Erskine and Davidson 1976; Erskine 1977);
5.0 HABITAT 5.1 Description of Habitats
• white spruce/trembling aspen/balsam poplar forest on steep slopes, with a tangled understorey of debris, young birch, and other shrubs (Enns and Siddle 1992);
Populations in different regions of North America occupy rather different forest-breeding habitats, although almost all descriptions of habitat include deciduous forest with a rich shrub layer. The Canada Warbler is considered a forest-interior bird in eastern North America (Robbins et al. 1989a), but in British Columbia, it appears to occur also at the edge of mature stands. In all regions, it nests on or very near the ground and
• “mature deciduous or mixedwood canopy, with a tall, dense, shrub layer, nearly always on a moist, rich site,” but were more common in mixedwood forest southwest of Dawson Creek (Lance and Phinney 1994).
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Ribes spp., Peltigera spp., kinnikinnick and single delight.
Of all the species considered by Enns and Siddle (1992), the Canada Warbler had the highest degree of fidelity to one habitat type, a deciduous-dominated mixed forest with at least 8% birch. This suggests that Canada Warblers require relatively specific breeding habitat qualities in northeastern British Columbia.
5.2 Nest Site Specialization
It is interesting to note that Canada Warblers in Maine used sapling stage deciduous forest after clearcutting (Titterington et al. 1979), but were not recorded in young aspen stands southwest of Dawson Creek (Lance and Phinney 1994). In east-central Alberta, Canada Warblers were not recorded at all in young (23-26-year-old) aspen forest either, but were found mainly in old-growth (>120 years) aspen forest and occasionally in mature (51-63 years) aspen forest (J. Schieck, pers. comm.)
Nest site microhabitat seems to be relatively specific throughout its range, although no data are available from British Columbia. Nests are bulky cups of dry leaves, grass, and plant fibre, lined with fine grass, rootlets, and hair. Nests are placed on or near the ground in moss-covered logs and stumps, under the overhang of stream banks, in grass hummocks, on the sides of mossy or fern-covered rocks, in overturned tree roots, or beside a clump of herbs (Bent 1953; Peck and James 1987).
Some common characteristics of Canada Warbler breeding habitat in British Columbia include (from sources listed above):
5.3 Distribution of Habitat
• paper birch (Betula neoalaskana and some hybrids of B.n. x papyrifera) is frequent.
The distribution of potential Canada Warbler habitat can be described with three general classifications (Biogeoclimatic Zones, Ecoregions, and Broad Habitat Classes) that are currently used in British Columbia.
• mixedwoods on slopes, often above riparian areas, or in floodplains where slopes were nearby. • seepages and wet sites, and in some locations standing water or fluvial channels are adjacent.
5.3.1 Biogeoclimatic Zones (BGZ) The Canada Warbler has been recorded in two variants of the Boreal White and Black Spruce (BWBS) Biogeoclimatic Zone: the BWBSmw1 variant (Peace Moist Cool Boreal White and Black Spruce) and the BWBSmw2 variant (Fort Nelson Moist Cool Southern Boreal White and Black Spruce) (DeLong et al. 1990; Meidinger and Pojar 1991). The BWBSmw1 is aligned generally with the Boreal Plains Ecoprovince and the BWBSmw2 is aligned generally with the Taiga Plains Ecoprovince (Demarchi 1993).
• colluvial material is common, with windthrown trees and debris indicating repeated “fall-down” disturbance. • deciduous trees were mainly dominant, but there was nearly always white spruce in association with the main tree layer. Shrubby understories with a high foliage height diversity dominated by soopolallie and rose (Rosa spp.), with red-osier dogwood, fireweed, saskatoon, northern bedstraw, choke cherry, wild sarsaparilla, pink corydalis, creamy peavine, American vetch, purple peavine, bluegrass (Poa spp.), fuzzy-spiked wildrye,
The BWBS is the most widespread BGZ in Canada (DeLong et al. 1990) and occupies virtually all of the Taiga Plains and Boreal Plains ecoprovinces. The BWBS also occurs west of the
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5.4 Present Habitat Availability
Rocky Mountains in northern British Columbia, mainly along major river valleys, but Canada Warblers do not occur there.
Habitat suitable for the Canada Warbler is probably fairly widespread in the middle and interior portions of the eastern Boreal Plains and Taiga Plains ecoprovinces, however it is restricted to slopes and floodplains subtended by slopes, which are in themselves fairly localized. These habitats are fragmented due to physiographic influences such as short breaks in slope, fluviation, or colluvial action. The effects of fire also contribute to the naturally fragmented nature of the habitat types used by Canada Warbler.
The Canada Warbler occurs primarily in the BWBSmw1 in British Columbia, mainly in ecotones between mesic and hygric site series. However, DeLong et al. (1990) include lodgepole pine in their classification of the mesic site series, but there are no records of Canada Warbler in British Columbia or Alberta from stands with lodgepole pine (Enns and Siddle 1992; Lance and Phinney 1993; Westworth and Telfer 1993; J. Schieck, pers. comm.). In the BWBSmw2 (Fort Nelson), site series may be more useful for predicting Canada Warbler habitat availability. The Cottonwood - currant - horsetail subhygric site series includes birch in the tree layer and a well-developed shrub layer in an upper river terrace position (Meidinger and Pojar 1991), features that are preferred by the Canada Warbler.
Mapping of these inventory type groups within broad scale landscape features such as floodplains and slopes subtending floodplains with dry to moist, old aspen is not available at present. As a means of identifying watersheds with a high potential for Canada Warbler suitability, Bonnor’s (1985) Landsat imagery classification was cross referenced with Shearwater’s (1994) mapping. In the Boreal Plains and Taiga Plains ecoprovinces, Canada Warblers can be predicted to occur in the following locations:
5.3.2 Ecoregions The Canada Warbler has been recorded in the following ecosections within its normal range in northeastern British Columbia (Figure 2):
• • • •
Whitemud River Notikewin River Fontas River Confluence of Sikanni Chief and Fontas rivers • Hay River • Shekilie River • Beatton River upper drainages
Boreal Plains Ecoprovince: Peace Lowland and Halfway Plateau ecosections. Taiga Plains Ecoprovince: Fort Nelson Lowland and Petitot Plain ecosections. It likely also occurs within other ecosections in the Boreal Plains and Taiga Plains ecoprovinces.
5.5 Trends in Quantity and Quality of Critical Habitat by Time
5.3.3 Broad Habitat Classes (BHC) Trends in habitat quality and quantity for Canada Warbler in the northeast are linked mainly with hardwood utilization by the forest industry, prescribed and uncontrolled fire regimes, flooding of riparian habitats and, to some extent, vegetation change. Note that Canada Warbler habitat has not been completely described in British Columbia.
The Canada Warbler has been recorded in four BHCs in the Boreal Plains and Taiga Plains ecoprovinces (Lea and Harcombe 1992). Descriptions of these BHCs and general abundances of each BHC in ecosections (Figure 2) where the Canada Warbler is known to occur are included in Table 1.
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Table 1. Broad Habitat Classes (BHCs) used by the Canada Warbler and general distribution of the BHCs in Ecosections within the Boreal Plains and Taiga Plains ecoprovinces (adapted from Lea and Harcombe 1992; Enns and Siddle 1992). Distributions are cross-referenced with Bonnor (1985). Broad Habitat Class and distribution in ecosections1
Description from Lea and Harcombe (1992)
BA Boreal White Spruce-Trembling Aspen
Typically a dense, broad-leaved, mixed or coniferous mixed forest, with shrub and herb dominated understories, which includes plant communities that succeed through trembling aspen seral forests to a white spruce climax. Includes all of the pure aspen areas around Fort St. John and Dawson Creek.
Distribution of BA in ecosections: PEL: widespread HAP: localized to widespread FNL: widespread PEP: rare
Typically a deciduous, mixed or coniferous forest with dense shrub understories, found on or in association with fluvial sites which include plant communities that succeed through deciduous forests to a white (or hybrid) spruce climax.
PR Boreal White Spruce-Balsam Poplar Riparian Distribution of PR in ecosections: PEL: widespread HAP: rare to localized FNL: localized PEP: localized AC Trembling Aspen Copse
Typically a dense, deciduous forest, with a shrubdominated understorey, which includes plant communities that succeed through shrub thickets to an edaphic climax of trembling aspen, found in association with shrub/grasslands.
Distribution of AC in ecosections: PEL: widespread to localized HAP: rare FNL: localized PEP: rare SB Boreal White Spruce-Paper Birch Slope
On slopes, often riparian, characterized by unstable materials with dense vegetation dominated by white spruce, rose and aspen. Birch always present. May correspond to the BAs subclass (from Shearwater Mapping 1994).
Distribution of SB in ecosections: PEL: localized HAP: rare FNL: localized PEP: rare
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PEL-Peace Lowland HAP-Halfway Plateau FNL-Fort Nelson Lowland PEP-Petitot Plain
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Mixedwood forests are being harvested at rates that the B.C. Forest Service tentatively recognizes as not sustainable (B.C. Ministry of Forests, Prince George Forest Region 1992). Loss of mixed cottonwood and spruce stands in riverbottom lands is occurring rapidly because they are in the greatest demand for harvesting in the Fort Nelson, Peace, and Dawson Creek Timber Supply Areas (TSA) (Massie et al. 1994). Ecotones between fluvial stands of merchantable mixedwood and alluvial slopes have an unpredictable susceptibility to change because of inherent instability of parent materials, i.e., colluviation. These areas also have a great potential for administrative-induced change to harvesting regulations. Such areas are relatively “easy” netdowns; they can be removed from the annual allowable cut early in the planning stages. Predictably, they occur on the border of merchantable mixedwood on fluvial channels, on the edge of alluvial and colluvial aprons, or on the midslope portions of slopes that are comparatively inoperable. Harvesting on slopes is not widespread in Canada Warbler habitat types, although it does occur.
Rates of habitat change can therefore be ranked as moderate to rapid in sloped areas. Further, the types of change are not the same for entire portions of habitat. Fires are infrequent to frequent with variable severity. On slopes, colluviation is ongoing but has a highly variable influence on vegetation longevity. As a result, many of the sloped stands used by Canada Warbler are of a mixed age class and are very patchy in both diversity and biomass development. In floodplains, intrinsic or natural rates of succession are also episodically controlled by floods, followed by relatively long periods of slow regrowth. In both floodplains and slopes, the abundant shrub layer common in all Canada Warbler habitat is able to quickly occupy spaces freed by colluviation or flooding. Birch is a rapid and therefore successful colonizer of these somewhat episodically unstable ecosystems.
Where habitat for Canada Warbler occurs within or adjacent to operable areas for logging, conversion to pure spruce is common (DeLong et al. 1990, p. 51). Management currently favours the production of moderately open- to closed-canopy aspen seral stages or mixedwoods, and the control and reduction of the tall, thicket-like shrub understorey that is negative for the Canada Warbler. Mixedwood site conversion is likely to influence Canada Warbler habitat. Simplistically speaking, deciduous-leading mixedwood is being converted to farmland in the south, conifer-leading mixedwood in the north and south, and juvenile cottonwood in the north.
5.7.1 Timber Supply Areas (TSA)
5.7 Legal Status of Habitat The legal status of lands with potential habitat for the Canada Warbler is discussed below.
Estimates of potentially suitable habitat in northeastern Timber Supply Areas (Figure 3) are given below (B.C. Ministry of Forests 1994; Massie et al. 1994): • Fort St. John TSA: 190 000 ha of aspendeciduous seral stages in age-classes 21-60 years. Older age-classes (>60 years) include an additional 300 000 ha. • Dawson Creek TSA: 223 000 ha of young to mature (21-100 years) deciduous forest. • Fort Nelson TSA: 28 000 ha of aspendeciduous forest types where spruce is a minor component (41-60 years).
5.6 Rate of Habitat Change The rate of change in habitat is linked with forestry effects, mainly harvesting of aspen stands, which is currently increasing. Demand for British Columbia hardwoods is expected also to increase in the future (Massie et al. 1994).
The above amounts of deciduous forest habitat should be considered as an overestimate of habitat that is suitable for the Canada Warbler. Only a 10
Provincial Parks Several Class A parks that are within the known range and habitat type of the Canada Warbler include:
portion will probably be suitable for the species. Much of the forest land inventory data and landbase availability described is probably intrinsically unsuitable to the Canada Warbler because of climate, elevation, and location. Pulpwood agreements 10 and 13, both with LouisianaPacific Panel Products Ltd., cover roughly 75% of the Dawson Creek and Fort St. John TSAs and approximately 20% of the Fort Nelson TSA.
• Beatton, northwest of Fort St. John (312 ha), in a trembling aspen upland.
5.7.2 Protected areas
• Taylor Landing, 16 km northeast of Fort St. John (2102 ha), in riparian mixedwood, and trembling aspen upland.
A few areas with habitat suitable for Canada Warblers are currently protected in British Columbia.
• Kiskatinaw River, 34 km northeast of Dawson Creek (1148 ha), in riparian cottonwood and mixedwood forest.
Figure 3. Timber Supply Areas in northeastern British Columbia. 11
harvesting methodologies (Forest Ecosystem Networks, Riparian Management Areas) are viable methods of protecting habitat. Wildlife Habitat Areas may be justifiable for this species in areas of concentration, but additional surveys are required to identify core populations.
• East Pine, 24 km east of Chetwynd (14 ha), in mixed deciduous riparian. Ecological Reserves Ecological Reserves with potentially suitable habitat include: • No. 8, Clayhurst on the Peace River near the Alberta border (316 ha), in dry aspen parkland.
6.0 LEGAL PROTECTION The Canada Warbler, its nests, and its eggs, are protected from direct persecution in Canada and the USA under the Migratory Birds Convention Act of 1994 and, in British Columbia, by the British Columbia Wildlife Act of 1982.
• No. 62, Fort Nelson River, 20 km northeast of Fort Nelson (121 ha), in cottonwood riparian forest. Proposed protected areas There are several areas with potential habitat that have been proposed as protected areas, including (proposed status uncertain):
The Biodiversity Field Guide of the Forest Practices Code (Forest Practices Code of British Columbia Act) states that riparian forest will be protected by establishment of riparian management areas along streams and wetlands, and that patches of old-growth forest will be retained to satisfy biodiversity needs. These reserves will help to protect some habitat if they are established in areas with breeding populations of Canada Warblers.
• Petitot River, a large area in the northeastern corner of B.C. (136 523 ha) in mixed wetland, spruce bog, and boreal trembling aspen. • Belcourt River, a large area in the southeastern border of the Boreal Plain south of Dawson Creek (37 441 ha) in a pine-aspen and mixedwood riparian.
7.0 LIMITING FACTORS The factors that are likely to limit populations of Canada Warbler in British Columbia are predominantly forest harvesting, stand conversion from mixedwood to pure stands, and the ensuing change in riparian and deciduous forest structure in the Boreal Plains and Taiga Plains ecoprovinces. There is considerable uncertainty surrounding the extent of these impacts however, and we have attempted to identify the uncertainties and discuss them.
Two old-growth riparian study areas of an indeterminate size are also proposed in the northeast, including: • Prophet River, an old growth riparian ecosystem including mixed cottonwood and white spruce. • Conroy Creek, an old growth riparian ecosystem including mixedwood riparian.
5.8 Can Critical Habitat be Protected by Means Other Than Acquisition?
7.1 Breeding Habitat The potential for extensive loss of deciduous forest habitat in the northeast is immense, given current plans to harvest deciduous forests. The Canada Warbler uses young to late seral stages with rich shrub layers. Whether or not it benefits
Habitat protection by way of Wildlife Habitat Areas (for other species), Protected Area initiatives (additional parks and reserves), and 12
7.2 Silviculture
from harvesting of old-growth aspen forest and coniferous forest, which stimulates shrub production, in British Columbia remains to be determined (see Titterington et al. 1979; Maurer et al. 1981). Another important positive factor is that the steep, unstable hillsides often preferred by this warbler in British Columbia (Enns and Siddle 1992) are unlikely to be harvested.
The forest management imperative in the northeast is unquestionably away from long rotations of mixedwood. The stands are increasingly prone to intensive silviculture to enhance one or the other of the deciduous versus the coniferous components of mixedwood (Delong et al. 1990; Delong 1991; Navratil et al. 1991). Techniques include “harvest with additional site preparation” and “assisted natural regeneration with site preparation and artificial seeding.” These techniques alter the shrub component, the debris structure and the eventual plant species distribution in the mixedwood stands. In some cases a separation in time is hoped for; deciduous wood in a first pass, followed by conifer harvesting in a second pass; the two-stage silvicultural system resulting in a controlled and prompt spruce regeneration (through combined natural regeneration and planting) after harvest of the parent mixedwood stand (Navratil et al. 1991). The impact that these techniques will have on the Canada Warbler is not known, but any technique that limits the diversity and density of understories will likely have a negative impact. Note that the long-term effects of mechanical site preparation on species composition and organic material in older stands is poorly known (Enns 1994).
Canada Warblers are known to be an area-sensitive species in some regions: their maximum probability of occurring (PO) in eastern North America being in contiguous forests >3000 ha in size; and their PO being reduced to 50% in forests of 400 ha (Robbins et al. 1989a). The smallest isolated forest where they have been recorded breeding was 187 ha (Robbins et al. 1989a). Given the above, it may seem incongruous that Canada Warblers are often found in edge habitat along roads in northeastern British Columbia. In British Columbia, our impression is that Canada Warblers are less sensitive to area effects than reported in other geographic regions. However, this relationship needs to be investigated further and should be considered tentative at present. Loss of forest habitat and forest fragmentation has been blamed for declines in Canada Warbler breeding populations in eastern North America. In general, loss of forest habitat and forest fragmentation has been widely blamed for declines in warbler breeding populations, and changes in overall bird community structure (e.g., Titterington et al. 1979; Whitcomb et al. 1981; Askins and Philbrick 1987; Askins et al. 1987; Blake and Karr 1987; Terborgh 1989). For example, elimination of forest adjoining a 23 ha reserve in Connecticut resulted in the gradual elimination of Canada Warblers as a breeding species (Askins and Philbrick 1987); and loss of surrounding forest was implicated in the extirpation of a breeding population (8 pairs/40 ha) in New York (Litwin and Smith 1992). Research on this subject is badly needed in British Columbia.
Thinning of shrub layers for silvicultural purposes will also likely cause Canada Warbler population declines (Askins and Philbrick 1987; Bock et al. 1993). Despite the advice given by DeByle (1991), management in boreal mixedwoods is not yet integrated to account for non-timber values.
7.3 Degree of Habitat Specialization In northern Maine, Canada Warblers were absent from recent clearcuts, but reoccupied patch clearcut areas between 7-12 years after harvesting when the seral forest was dominated by deciduous trees 2-4.5 m tall, but less than 10 cm dbh. Maximum densities were reached when seral forests were >12 years old and were dominated by
13
probability of predation on forest songbird nests increases with increasing forest fragmentation (Wilcove 1985; Yahner and Scott 1988; Askins et al. 1990), it is likely that Canada Warblers will face increasing predation intensity as forests are cleared.
deciduous trees >4.5 m tall with 10-15 cm dbh (Titterington et al. 1979). Canada Warblers disappeared when forests reached a mature stage dominated by conifers (northern Maine; Titterington et al. 1979), and density of shrub layers decreased substantially (Connecticut; Askins and Philbrick 1987). These results should suggest that clearcutting of coniferous and old-growth aspen stands may increase habitat for Canada Warblers, if deciduous stands are allowed to colonize. However, in British Columbia and Alberta, Canada Warblers were found mainly in mature and old-growth aspen forests, and have not been found in young stages (Westworth and Telfer 1993; Lance and Phinney 1994; J. Schieck, pers. comm.).
7.6 Grazing Canada Warblers inhabit forests with a rich ground cover of shrubs and herbs. High-intensity grazing by cattle will destroy much of the structural integrity of the lower shrub and herb layer in local sites and seriously degrade potential habitat. Grazing, thinning or control of shrub layers is a potential cause of population decline for grounddwelling species dependent on rich understories (see Askins and Philbrick 1987; Bock et al. 1993). Cattle also attract cowbirds.
7.4 Brown-headed Cowbird Parasitism
7.7 Agriculture
The impact of nest parasitism by Brown-headed Cowbirds is thought to be severe on neotropical migrant songbirds, especially in fragmented forests (Brittingham and Temple 1983; Askins et al. 1990; Robinson et al. 1993). Canada Warblers are known to be parasitized regularly by cowbirds when the two species occur together (Friedmann et al. 1977). There is one case of parasitism reported for northeastern British Columbia where adults were found feeding a fledged cowbird (Siddle 1992). Current trends in populations of Brown-headed Cowbirds in the northeast are not known for certain, but the probability that cowbirds will parasitize Canada Warbler nests can only increase with increasing fragmentation of northeastern forests.
Many of the pure aspen stands of large stem size occur on private lands adjacent to agricultural fields in the Dawson Creek TSA. Harvesting is currently taking place on private lands and an unknown proportion of these lands is being converted to agriculture. Clearings also attract cowbirds, crows, and magpies.
7.8 Urban Development Urban development has not advanced as rapidly in the range of the Canada Warbler as in other areas of British Columbia, but human settlements attract predators such as jays, crows, magpies, squirrels, and also introduce domestic cats as a predator. In the Fort Nelson area, increased land industrialization is planned in areas with Canada Warbler records.
7.5 Predation Fragmentation through clearing of land, road building, seismic line clearing, etc., also increases edge habitat favoured by predatory avian species. Blue Jays, American Crows, and Black-billed Magpies are most numerous around farms, urban areas, and edges of other cleared areas and are least numerous in unbroken forest. Because the
7.9 Prescribed Fire Prescribed fire may be used to remove what foresters may perceive as “decadent old aspen stands,” or to improve ungulate foraging habitat
14
gas exploration (and SO2 venting) is expected in the northeast, but the threshold for healthy stands of deciduous Canada Warbler habitat is unknown.
on slopes. An issue that is certain to be contentious is the conflict between management for big-game species and neotropical migrants in the northeast. Wildlife management in the northeast has focused mainly on management of mammals that are hunted (elk, mountain sheep, moose, caribou, mountain goat, deer, bison, bears, wolves). Studies in other areas have found that management for high-profile wildlife like these can be incompatible with management for neotropical migrants. For example, in Idaho, most habitat management on public lands was focused on elk, a habitat generalist species (Groves and Unsworth 1993). When the effect of habitat management for elk was analyzed for its affect on neotropical migrants, which are usually habitat specialists, most management techniques were found to be counterproductive for the latter. The needs of neotropical migrants were not being met. In British Columbia, techniques, such as prescribed burns to improve forage for ungulates, may severely damage the structural heterogeneity of shrub layers that are critical for Canada Warblers. Although this point may be moot, because prescribed burns may not often be set in areas known to be frequented by Canada Warblers, further research into their distribution may show areas of conflict.
7.11 Seismic Lines and Roads Gas and oil exploration in the Fort Nelson area has dramatically increased to the extent that the B.C. Ministry of Forests inventory branch has attempted to calculate the impact on the wood supply (B.C. Ministry of Forests 1992). This analysis indicates that all forest types, including those mixedwood, birch, trembling aspen, balsam poplar and cottonwood-leading stands with a spruce understorey, have measurable removals. As Canada Warblers appear to utilize openings in mixedwoods, this may be advantageous for the birds' use of more remote habitats, but may also attract increased numbers of predators and cowbirds.
7.12 Winter Habitat Canada Warblers winter in montane forests of northwestern South America from Venezuela south to Peru. Loss of forest habitat (about 2% annually) is a widespread problem for neotropical migrants in Latin America and is undoubtedly of long-term significance for Canada Warblers (Rappole et al. 1983; Ehrlich et al. 1988; Terborgh 1989; Finch 1991; Hartshorn 1992). Short-term effects of habitat loss may be tempered, compared to some other species, by the belief that Canada Warblers tolerate a certain degree of habitat alteration on their winter range (Terborgh 1989). Because of the concentration of migrants from huge breeding distributions into relatively smaller wintering ranges (Terborgh 1980), if the rate of habitat loss is accelerated in South America, then the effects on Canada Warbler populations will also accelerate. For British Columbia populations, we believe it is obvious that effects of habitat loss on the wintering grounds are substantially less significant than the loss of habitat in the northeast.
7.10 Air Pollution Mapping of pulpwood, oil- and gas-related emissions in the northeast (Parfitt 1994) indicates an overlap with Canada Warbler habitat in the Fort Nelson, Dawson Creek, and Fort St. John areas. Emissions from sour-gas processing, exploration well venting, and the kraft pulping process, (e.g., SO2, NOx, H2S, TRS, and particulate matter) have relatively severe effects on trembling aspen, and cottonwood in comparison to other species (Malhotra and Blauel 1980). Trembling aspen near Alberta sour-gas processing plants show increased mortality in high-impact zones, a higher incidence of Armillaria root-rot and Hypoxylon canker, as well as depression of annual volume increments (Maynard et al. 1994.). A somewhat unpredictable, but voluminous, increase in sour-
15
8.0 SPECIAL SIGNIFICANCE OF THE SPECIES
creation of Wildlife Habitat Areas in areas of concentration may also be appropriate, especially if several pairs are present. The WHAs should be relatively large (minimum 500 m diameter) so as to discourage parasitism by Brown-headed Cowbirds and predation by corvids. Linear-shaped WHAs, probably on slopes above streams, such as along the banks of the Peace River, would likely be best.
8.1 Status The Canada Warbler is widespread across much of Canada east of the Rocky Mountains, and in the northeastern USA (Godfrey 1986). In British Columbia, it is a relatively new member of our provincial avifauna and is restricted to the Boreal Plains and Taiga Plains ecoprovinces. Populations are local, but in suitable habitat appear to be fairly common. The Canada Warbler should be considered to be an uncommon and local summer visitant and breeder in the province.
If we assume that the goal of managing for biodiversity is to maintain natural populations and patterns across broad landscapes, then a number of general guidelines apply (Hutto et al. 1993). 1. Manage for desired landscape patterns with a clear picture of land-use trends and conditions over a broad landscape, not by harvest-byharvest decisions.
8.2 Degree of Public Interest The Canada Warbler is highly valued by birdwatchers because of its beauty and rarity. It is relatively “showy” and has a musical song. It is a “highlight” bird on any trip to the northeast. In migration, it is probably seen occasionally in suburban yards, but otherwise it likely goes unnoticed by the public.
2. Allow natural processes to occur: fire, insect outbreak, blowdowns, etc., because the adaptive histories of most species in natural ecosystems are linked to natural periodic disturbances. 3. Use knowledge of local ecology and be wary of extrapolating results from other regions; probably an important point to consider for Canada Warblers in British Columbia.
8.3 Related Species A closely related species, the Wilson’s Warbler, is a common and widespread breeder and migrant in most regions of British Columbia.
4. Manage for multiple-species except when single species become species of special concern (e.g., Red and Blue List).
9.0 RECOMMENDATIONS AND MANAGEMENT OPTIONS
5. Monitor populations of forest birds to keep current on effects of silvicultural practices.
Several guidelines for maintaining mature and old-growth deciduous forest that are contained in the Biodiversity Field Guide of the Forest Practices Code will be helpful in maintaining habitat for Canada Warblers in British Columbia. Because populations are local, and pairs may be fairly common in those areas, then Oldgrowth Management Areas and Riparian Management Areas centred on Canada Warbler populations would help maintain habitat for this species. The
Three other general principles provided by Robbins et al. (1993) are appropriate for management of Canada Warbler habitat: 1. Promote microhabitat diversity by providing uneven-aged forests and precluding grazing by domestic stock which destroys the ground layer.
16
6. Banding studies to determine site fidelity and population dynamics.
2. Preserve as much old-growth as possible. 3. Promote public awareness of the plight of neotropical migrants. Project Wild would be one appropriate vehicle for education programs in British Columbia.
11.0 EVALUATION In British Columbia, the Canada Warbler has small, possibly expanding, localized populations in the northeast. In suitable habitat it is fairly common, but these areas are limited. Because of uncertainties regarding its relative use of different habitats (mixedwoods, pure deciduous stands, brushy areas), the impact of increased timber harvesting is difficult to estimate. Because of its utilization of relatively steep hillsides and younger seral stages, it may be at less risk of habitat loss than several other species of northeastern warblers that are restricted to mature forests (e.g., Black-throated Green, Connecticut, and Cape May warblers). Very few breeding pairs are probably protected by existing reserves, and there are few data on distribution and reproductive parameters.
Habitat corridors that connect isolated patches of forest with continuous forest are proving to be an important factor in retaining bird community diversity in those isolated patches (MacClintock et al. 1977), especially for ground-nesting species like the Canada Warbler. Provision of corridors (i.e., Riparian Management Areas) of habitat suitable for Canada Warblers between forest reserves may reduce the impact of clearcutting. Before prescribed fires are set for ungulate range management purposes, the needs of neotropical migrants such as the Canada Warbler should be considered.
10.0 RESEARCH REQUIREMENTS
Thompson et al. (1993) rank Canada Warblers as 23rd out of 110 midwestern North American species of neotropical migrants for management priority, mainly because of population declines and threats on its wintering grounds. Smith et al. (1993) rank it the 11th out of 82 neotropical migrant species for management priority in northeastern North America, for the same reasons. However, Reed (1992) suggests it has a very low probability of extinction, overall. Our outlook for this species in British Columbia, is more optimistic than for Connecticut, Black-throated Green, Cape May and Bay-breasted warblers, but is tempered by a lack of knowledge on the effect of timber harvesting on habitat quality (Table 2).
Additional research is required to improve our ability to manage habitat for Canada Warblers in British Columbia. 1. Further inventory work is required to determine the extent of distribution and location of core populations. 2. Research on habitat utilization including relative use and comparative breeding success in different-aged seral stands and forest types. This research is critical for determining the impact of large-scale aspen forest harvesting.
Because of its limited distribution, small populations, uncertainties around the effect of forestry practices on habitat quality, and lack of protected areas the Canada Warbler should be considered Vulnerable and should remain on the Blue List.
3. Studies on the effect of grazing on habitat quality. 4. Migration surveys to determine habitat use during non-breeding periods. 5. More research on the impact of cowbird parasitism. 17
Table 2. Comparison of six rare songbirds restricted to northeastern British Columbia. Species are ranked in order of conservation priority. Population Size and Distribution
Species
Recommended Status
Primary Habitat
Major Threats
Connecticut Warbler
Red
Old-growth aspen forest
Logging Agriculture Silviculture Fragmentation
Small and local
Black-throated Green Warbler
Red
Old-growth riparian mixedwoods
Logging Fragmentation
Small and local
Cape May Warbler
Red
Old-growth spruce forest
Logging
Very small and scattered
Bay-breasted Warbler
Red
Old-growth spruce forest
Logging
Very small and scattered
Canada Warbler
Blue
Mature/old-growth aspen forest
Logging Fragmentation Silviculture
Small and local
Philadelphia Vireo
Blue
Habitat generalist
Fragmentation
Small and local
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Groves, C.R., and J.W. Unsworth. 1993. Wapiti and Warblers: integrating game and nongame management in Idaho. Pages 408-417 in D.M. Finch and P.W. Stangel, eds. Status and management of neotropical migratory birds. Gen. Tech. Rep. RM-229. U.S. Dep. Agric. For. Serv., Fort Collins, CO.
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Massie, M.R.C., E.B. Peterson, N.M. Peterson and K.A. Enns. 1994. An assessment of the strategic importance of the hardwood resource in British Columbia. FRDA Report 221. Canada-British Columbia Partnership Agreement on Forest Resource Development: FRDA II. Victoria, BC. 206pp.
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Maurer, B.A., L.B. McArthur and R.C. Whitmore. 1981. Effects of logging on guild structure of a forest bird community in West Virginia. Am. Birds 35:11-13.
Lea, E.C., and A.P. Harcombe. 1992. Wildlife habitats of British Columbia. B.C. Minist. Environ., Lands and Parks, Wildl. Branch. Victoria, BC. 5pp.
Maynard, D.G., J.J. Stadt, K.I. Mallett and W.J.A. Volney. 1994. Sulphur impacts on forest health in west-central Alberta. Nat. Resour. Can., Can. For. Serv. Northwest Reg., North. For. Cent. Edmonton, AB. NOR-X-334. 54pp.
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Meidinger, D., and J. Pojar. 1991. Ecosystems of British Columbia. Spec. Rep. Ser., No. 6. B.C. Minist. For., Victoria, BC. 330pp. Morse, D.H. 1973. The foraging of small populations of Yellow Warblers and American Redstarts. Ecology 54:346-355.
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Peterson, E.B., and N.M. Peterson. 1992. Ecology, management, and use of aspen and balsam poplar in the prairie provinces, Canada. Spec. Rep. 1. Northern For. Can. Northwest Reg. Northern For. Centre. 252pp.
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Witham, J.W., and M.L. Hunter Jr. 1992. Population trends of neotropical migrant landbirds in northern coastal New England. Pages 85-95 in J.M. Hagan III and D.W. Johnston, eds. Ecology and conservation of neotropical migrant landbirds. Smithsonian Inst. Press, Washington, DC.
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24
Wildlife Working Reports may be cited, but the preliminary nature of the data they contain should be noted. Working Reports 1-15 (and others) are presently out of print, but photocopies may be available through the Wildlife Branch, Ministry of Environment, Lands and Parks.
WR-26
Quesnel Highlands wolf control project. D. Hebert. January 1987. 10pp.
WR-27
Muskwa Wolf Management Project of northeastern B.C. 1986-87 annual report. J.P. Elliott. April 1987. 20pp.
WR-28
Vancouver Island wolf control project. Year 1 progress report. D. Janz. July 1987. 11pp.
WR-29
Habitat survey of the Mackenzie Heritage Trail corridor. V. Hignett. June 1987. 21pp + 5 maps.
WR-30
A proposal to manage coyote and cougar populations of the Junction Wildlife Management Area. D. Hebert. September 1987. 11pp.
WR-31
Wildlife habitat suitability of the Mackenzie Heritage Trail corridor. V. Hignett. May 1988. 16pp + 6 maps.
WR-32
Research priorities for furbearers in British Columbia. D. Blood. June 1988. 49pp.
WR-33
Electrically triggered drop net to capture wild sheep. J.W. Hirsch. January 1988. 18pp.
WR-34
A lynx management strategy for British Columbia. D.F. Hatler. July 1988. 121pp.
WR-35
Causes of bighorn sheep mortality and dieoffs - literature review. H.M. Schwantje. April 1988. 54pp.
WR-36
Explanatory legend for vegetation maps of the Kamloops Lake bio-physical study area. E.C. Lea. December 1988. 78pp.
WR-37
Bio-physical habitat units and interpretations for moose use of the upper Cariboo River Wildlife Management Area. E.C. Lea, T. Vold, J. Young, M. Beets, D. Blower, J. Youds, A. Roberts. December 1988. 24pp.
WR-38
Grizzly bear habitat of the Flathead River area: expanded legend. E.C. Lea, B.L. Fuhr, and L.E.H. Lacelle. December 1988. 24pp.
WR-39
Managing habitat through guidelines: How far can you go? M. Fenger and V. Stevens, eds. February 1989. 48pp.
WR-40
Wolf-prey dynamics. Proceedings of a symposium sponsored by B.C. Ministry of Environment, Wildlife Branch, Faculty of Forestry, University of British Columbia and the Northwest Wildlife Preservation Society. February 1989. 188pp.
WR-41
Caribou research and management in B.C.: proceedings of a workshop. R.Page, ed. November 1988. 275pp. (Also printed as WHR-27)
WR-42
Trapping in British Columbia - a survey. R. Reid. January 1989. 55pp.
WR-43
Biophysical habitat units of the Lower Halfway study area: expanded legend. E.C. Lea and L.E.H. Lacelle. December 1989. 33pp.
WR-44
Long range habitat planning: proceedings. M. Fenger and V. Stevens, eds. March 1990. 49pp.
WR-45
Biophysical habitat units of the Mosley Creek study area: expanded legend and interpretations. E.C. Lea and R.C. Kowall. March 1990. 33pp.
WR-46
Habitat Management Section. Annual General Meeting. Yellowpoint Lodge - 1989 April 25-27. Wildlife and Recreational Fisheries Branches, Ministry of Environment. July 1990. 107pp.
WR-47
Working plan — Khutzeymateen Valley grizzly bear study. A.N. Hamilton and J.A. Nagy. September 1990. 35pp. (Also printed as WHR-28).
WR-48
Khutzeymateen Valley grizzly bear study. Annual progress report - year 1 (1989/90), annual working plan - year 2 (1990/91). J.A. Nagy and A.G. MacHutchon. January 1991. 44pp. (Also printed as WHR-29).
WR-49
Fort Nelson and area average winter maximum snowpack mapping. R. Chilton. July 1990. 12pp.
WR-50
Marten habitat suitability research project - working plan. E.C. Lofroth and V. Banci. January 1991. 31pp.
WR-51
Khutzeymateen Valley grizzly bear study. Annual progress report - year 2 (1990/91), annual working plan - year 3 (1991/92). A.G. MacHutchon and S. Himmer. March 1992. 36pp. (Also printed as WHR-30)
WR-52
Abundance, Distribution and Conservation of Birds in the Vicinity of Boundary Bay, B.C. R.W. Butler, ed. 1992. 132pp. (Also printes as Technical Report Series No. 155, Pacific and Yukon Region, Can. Wildlife Service).
WR-53
Status of the Clouded Salamander in British Columbia. T.M. Davis and P.T. Gregory. March 1993. 19pp.
WR-54
Status of the Northern Pacific Rattlesnake in British Columbia. M.B. Charland, K.J. Nelson, P.T. Gregory. March 1993. 23 pp.
WR-55
Status of the Shrew-mole in British Columbia. L. Kremsater, L. Andrusiak, F.L. Bunnell. March 1993. 26 pp.
WR-56
Status of the Nuttall’s Cottontail in British Columbia. D.W. Carter, A. Harestad, F.L. Bunnell. March 1993. 33 pp.
WR-57
Status of the Sharp-tailed Snake in British Columbia. D.J. Spalding. March 1993. 15pp.
WR-58
Guidelines for Technical Publications of the Wildlife Program. E. Stanlake. March 1993. 57pp.
WR-59
Status of Keen's Long-eared Myotis in British Columbia. M. Firman, M. Getty, and R.M.B. Barclay. March 1993. 29pp.
Continued from inside back cover: WR-60
Biophysical Habitat Units for the Tatlayoko Lake Study Area: expanded legend and interpretations. E.C. Lea and R.C. Kowall. March 1993. 22pp.
WR-61
Status of the Pallid Bat in British Columbia. K. Chapman, K. Mc Guinness, R.M. Brigham. February 1994. 32pp.
WR-62
Status of the Bald Eagle in British Columbia. D.A. Blood and G. G. Anweiler. February 1994. 92pp
WR-63
A Survey of the Bat Fauna of the Dry Interior of British Columbia. S.L. Holroyd, R.M.R. Barclay, L.M. Merk, and R.M. Brigham. March 1994. 80pp.
WR-64
Distribution and Abundance of Four Species of Small Mammals At Risk in a Fragmented Landscape. G.A. Zuleta and C. Galindo-Leal. March 1994. 80pp.
WR-65
Problem Analysis of Integrated Resource Management of Riparian Areas in British Columbia. S.L. Rautio, P. Bunnell. March 1994. 26pp. (Also RRP3003-HQ Minist. of For. Res. Br.)
WR-66
A Bibliography of Selected Literature on Wildlife Trees with Annotations and Abstracts. Wildlife Tree Committee. December 1994. 90pp.
WR-67
Status of the Vaux's Swift in British Columbia. K. Summers and M. Gebauer. March 1995. 24pp.
WR-68
Status of the White-throated Swift in British Columbia. K. Summers. March 1995. 24pp.
WR-69
Status of the Williamson's Sapsucker in British Columbia. J.M. Cooper. March 1995. 24pp.
WR-70
Status of the Sharp-tailed Grouse in British Columbia. R. Ritcey. March 1995. 52pp.
WR-71
Status of the Western Harvest Mouse in British Columbia. D.W. Nagorsen. March 1995. 32pp.
WR-72
Status of the Badger in British Columbia. A.H. Rahme, A.S. Harestad and F.L. Bunnell. March 1995. 64pp.
WR-73
Status of the Fringed Myotis in British Columbia. S.A. Rasheed, P.F.J. Garcia, and S.L. Holroyd. October 1995. 28pp.
WR-74
Status of the Western Small-footed Myotis in British Columbia. P.F.J. Garcia, S.A. Rasheed, and S.L. Holroyd. October 1995. 24pp.
WR-75
Status of the Spotted Bat in British Columbia. P.F.J. Garcia, S.A. Rasheed, and S.L. Holroyd. October 1995. 24pp.
WR-76
The Distribution, Abundance, and Habitat Requirements of Selected Passerine Birds of the Boreal and Taiga Plains of British Columbia. K.A. Enns and C. Siddle. March 1996. 54pp.
WR-77
Status of the Brewer's Sparrow (breweri subspecies) in British Columbia. M.J. Sarell and K.P. McGuinness. March 1996. 22pp.
WR-78
Status of the Green Heron in British Columbia. D.F. Fraser and L.R. Ramsay. March 1996. 28pp.
WR-79
Status of the Bay-breasted Warbler in British Columbia. J.M. Cooper, K.A. Enns, and M.G. Shepard. February 1997 36pp.
WR-80
Status of the Black-throated Warbler in British Columbia. J.M. Cooper, K.A. Enns, and M.G. Shepard. February 1997. 36pp.
WR-81
Status of the Canada Warbler in British Columbia. J.M. Cooper, K.A. Enns, and M.G. Shepard. February 1997. 36pp.
