Jameson F. Chace^1,2,3*, Steven D. Faccio^3,5, and Abraham Chacko¹

Abstract- We examined habitat used by Wilsonia canadensis (Canada Warbler), a migratory songbird population in a 40-year decline. We used a long-term forest bird monitoring program in Vermont to compare the structural components of sites of warbler presence and absence. Habitats occupied included lowland Picea-Abies (spruce-fir), northern hardwood, and Quercus-Carya (oak-hickory) forests, and Acer rubrum-Thuja (Red Maple-cedar) and cedar-fir swamps. Northern hardwood forest detections were explored in greater detail due to the greater extent of coverage in Vermont, the higher number of survey points (n = 80), and high percentage of Canada Warbler detections at those points (29%). Within the northern hardwood forests, warblers occurred in patches with a lower canopy height and higher percentage ground cover of shrubs and ferns than patches where warblers were not detected. These three parameters were also the strongest set of competing Akaike's information criterion model scores based on the patch attributes. In the northern hardwoods of the north-east, the conditions of reduced average canopy height and increased ground cover are created naturally by wind throw, ice storms, and insect damage, as well as under some forms of timber management. Canada Warblers appear to prefer these forest structural conditions because they provide abundant foraging strata, conceal nesting sites, and expose song perches.

Read the rest of the paper here (9mb, .pdf)

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Developing Conservation and Forest Management Guidelines for Canada Warblers in the Atlantic Northern Forest

Steven D. Faccio¹, J. Daniel Lambert¹, Jameson F. Chace², and Leonard J. Reitsma³

¹ Conservation Biology Department, Vermont Institute of Natural Science, Woodstock, VT 05091
2 Environmental Studies Program, Department of Biology, Villanova University, Villanova, PA 19085
3 Natural Science Department, Plymouth State University, 17 High Street, Plymouth, NH 03264-1595

sfaccio at vinsweb.org
dlambert at vinsweb.org
jameson.chace at salve.edu
leonr at plymouth.edu

Introduction

The Canada Warbler (Wilsonia canadensis) is a neotropical migrant songbird that winters in South America and breeds in the northeastern United States, southeastern Canada, and in boreal forests extending west into Alberta. In the Atlantic Northern Forests of New England, the species inhabits a variety of upland and lowland habitats, including red maple swamps, northern white cedar swamps, mixed forests, and lowland spruce-fir forests (Conway 1999). Despite its apparent wide tolerance of habitat types, the species is patchily distributed, typically at low densities, throughout the Northeast, which comprises a significant portion of its global range. In addition, Canada Warbler has exhibited steep population declines, with trend estimates ranging between -2.4% (Rosenberg and Hodgman 2000) and -13.2% per year (Faccio et al. 1998).

Responding to these data, the Northeast Endangered Species and Wildlife Diversity Technical Committee, Partners in Flight, and the North American Bird Conservation Initiative (NABCI) recently identified Canada Warbler as one of the region’s highest priorities for conservation and research (Therres 1999, Rosenberg and Hodgman 2000, USFWS 2003). A recent study in Vermont showed that Canada Warblers are sensitive to small changes in the forest canopy, responding positively to ice storm-created gaps in the Green Mountain National Forest (Faccio 2003). Additionally, recent support from the Sweet Water Trust enabled the Vermont Institute of Natural Science (VINS) and collaborator Dr. Jameson Chace (Villanova University) to take an initial step in quantifying the habitat requirements of the Canada Warbler (Faccio and Chace, unpublished data). However, since the species utilizes a variety of forest types, the need for additional breeding-ground research comparing reproductive rates among vegetation types is acute. Such an investigation is necessary to identify land protection priorities and develop stewardship guidelines that promote nesting success.

Methods

In 2003, VINS and Dr. Jim Chace initiated a collaborative project with Dr. Leonard Reitsma (Plymouth State University), to continue investigations of the habitat requirements and breeding biology of this little- known neotropical migrant. Data were collected on behavior, territories, and productivity from nearly 50 Canada Warblers at 3 study sites located in New Hampshire and Vermont (Fig. 1). Field studies in New Hampshire were conducted at the Canaan Town Forest, and the abutting Bear Pond Natural Area (which was recently conserved with funds from the Sweet Water Trust). In Vermont, field work focused on the Nulhegan Basin Division of the Silvio O. Conte National Fish and Wildlife Refuge in the town of Lewis. These study areas total over 27,000 acres and contain a variety of managed and unmanaged habitats. The project’s specific conservation goals are to:

• Describe and compare Canada Warbler habitat requirements among different forest communities.
• Determine which habitat characteristics promote nesting success.
• Identify priority habitats for conservation.
• Evaluate the potential for forest management to produce favorable breeding conditions.
• Develop a set of best forest management practices for Canada Warbler.
• Provide outreach materials to land protection organizations, foresters, and other natural resource professionals.

During the pilot season, three Plymouth State undergraduates helped us collect habitat metrics from over 100 vegetation plots. We also constructed a geographic information systems (GIS) database to store, manage, and display the information. Preliminary data analysis is focused on comparing habitat composition and structure at occupied territories vs. unoccupied sites, and at successful territories vs. unsuccessful territories. Results of this analysis are pending, but our predictions, based on hundreds of hours of observation, are that Canada Warbler abundance and productivity will be positively associated with high shrub density, semi-open canopy, and moist soil.

The collaborators on this project are continuing the investigation during the 2004 breeding season:

1. capture and color-band 20-30 males as they arrive on territories in both managed and unmanaged habitat;
2. recapture or resight males returning from the previous breeding season;
3. age males based on plumage characteristics;
4. document each male’s movement and behavior during six continuous, 30-minute observation periods between 25 May and 10 July;
5. determine the reproductive status of males at three stages of the breeding cycle (pairing, nesting, fledging);
6. delineate territory boundaries based on geo-referenced positions of observed males, collected at 5-minute intervals;
7. verify accuracy of territory-mapping method with radio-telemetry;
8. measure over 40 habitat variables on four plots within each territory and on paired plots located in unoccupied habitat;
9. maintain a geographic information systems database to manage the information.

Results

Once the field season is complete, we will employ standard statistical procedures to determine which habitat characteristics underlie patterns of distribution, abundance, demographic structure, and rates of pairing, nesting, and fledging success. Results of this analysis will be used to:

1. describe Canada Warbler habitat requirements;
2. determine which habitat characteristics promote nesting success;
3. identify priority habitats for conservation;
4. recommend stewardship practices that promote favorable breeding conditions.

Stewards of the three study areas (the Canaan Conservation Commission, Mascoma Watershed Conservation Council, and US Fish and Wildlife Service) support this work and have expressed interest in using the results to better manage their holdings for Canada Warbler and other songbirds. We also plan to advise conservation and natural resource professionals throughout the Northeast on how to meet the breeding requirements of this vulnerable species. This will be achieved through development of two outreach products which will be distributed directly to conservation groups, as well as to public and private land managers. These products will consist of a technical report detailing our methodology, results and recommendations, as well as a concise pamphlet highlighting best management practices that will meet the breeding requirements of this vulnerable species. Additionally, information will be disseminated to ornithologists and conservation biologists through submissions to peer-reviewed journals, conferences, and participation in professional meetings, including Partners in Flight, NABCI, and Important Bird Areas.

Results of the field study will focus limited conservation resources on areas within the Atlantic Northern Forest that have high ecological value for the Canada Warbler, as well as for other species that share its habitat. In addition, our findings will help timberland owners to enhance Canada Warbler breeding habitat through specific management prescriptions. Finally, this research will build a foundation for future studies of Canada Warbler that will enable refined approaches to the species’ protection.

Literature Cited

Conway, C. J. 1999. Canada Warbler. In The Birds of North America, No. 421 (A. Poole and F. Gill, eds.). The Birds of North America, Inc. Philadelphia, PA.

Faccio, S. D. 2003. Effects of ice storm-created gaps on forest breeding bird communities in Central Vermont. Forest Ecology and Management 186:133-145.

Faccio, S. D., C. C. Rimmer, and K. P. McFarland. 1998. Results of the Vermont Forest Bird Monitoring Program, 1989-1996. Northeastern Naturalist 5:293-312.

Rosenberg, K. V., and T. P. Hodgman. 2000. Partners’s In Flight Landbird Conservation Plan: Physiographic Area 28: Eastern Spruce-fir. Version 1.0. American Bird Conservancy, The Plains, VA.

Therres, G. D. 1999. Wildlife species of conservation concern in the Northeastern United States. Northeast Wildlife 54:93-100.

US Fish and Wildlife Service (USFWS). 2003. North American Bird Conservation Initiative: Bird Conservation Region Descriptions. Division of Bird Habitat Conservation, Arlington, VA.

Figure 1. Location of Canada Warbler study sites in Vermont and New Hampshire. Click location to view detail map.

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