Canada warblers prefer shrubby habitats.
Nearly 10 years ago, an analysis by the Vermont Forest Bird Monitoring Program (FBMP) revealed that Canada warblers were declining significantly on study sites across the state. The warbler was also found to be declining on North American Breeding Bird Survey routes throughout the Northeast, and very little was known at the time about its breeding ecology and habitat needs. Red flags were dutifully raised.
In an effort to address these concerns, conservation biologists Dan Lambert and Steve Faccio of the Vermont Institute of Natural Science collaborated with Jim Chace, now of Salve Regina University in Newport, Rhode Island, and Leonard Reitsma of Plymouth State University on a study of Canada warbler breeding ecology. Since 2001, the biologists have been investigating Canada warblers at a variety of study sites in Vermont and New Hampshire, including mature forests, a spruce-fir swamp, and a variety of managed forests. The team has conducted point counts, color-banded and radio-tracked individual birds, delineated territories, collected thousands of insect prey samples, measured innumerable trees and shrubs, and assessed the reproductive status of Canada warblers at these locations.
The results of these studies confirm the importance of high shrub density in Canada warbler habitat selection and also confirm that more warblers tend to occupy areas with denser ground cover. In these areas, territory sizes were generally smaller than those in upland, cutover areas, where larger territories helped compensate for a paucity of shrubby, food-rich habitat. Upland and wetland birds both exhibited high rates of pairing and fledging success (86-92 percent); however, territory density was greater in the swamp, where small and overlapping territories suggested an ample resource supply. If reproductive rates are comparable in managed and natural habitats, then density could, in fact, be an appropriate gauge of habitat quality for Canada warblers.
From their results, the researchers have produced a report, entitled Canada Warbler: Population Status, Habitat Requirements, and Stewardship Guidelines for Northeastern Forests, which is a practical, on-the-ground handbook for resource managers. This handbook recommends conserving swamp and riparian habitats as well as regenerating forest patches and hardwood or conifer stands with structurally complex floors. The full report can be downloaded at the CBD website at: www.vinsweb.org/cbd/CAWAresearch.html.