KIRTLAND'S WARBLER BREEDING BIOLOGY AND HABITAT MANAGEMENT

—The Kirtland's warbler (Dendroica kirtlandii) is an early succession, area-sensitive species seldom found in stands smaller than 30 to 40 ha. This warbler occupies dense jack pine (Pinus banksiana) stands where trees are from 6 to 23 years old and from 1.7 to 5.0 m high growing on poor, sandy soils. Typically, it has been found in areas regenerated naturally by serotinous cones resulting from wildfires. In the past 2 decades, however, Kirtland's warblers have been found in naturally regenerated, unburned jack pine and in densely stocked pine plantations. Stands are managed on a 50-year rotation and clustered into discrete management areas. Extensive dispersal to find suitable habitat reduces breeding opportunities. Currently, about 15 percent of the males abandon territories, and about 15 percent of the resident males do not find mates. Clustering stands into management units and staggering the schedule of stand regeneration should minimize biogeographic dispersal problems. Because Kirtland's warblers colonize patches of taller, dense jack pine before they occupy habitat with shorter or less dense trees, the period of Kirtland's warbler occupancy in a management area can be extended by several methods such as varying tree spacing in a plantation. Researchers and managers have developed a variety of harvest options, site preparation methods, and pine regeneration alternatives for providing suitable Kirtland's warbler habitat. Several options do not require the use of prescribed fire. These management alternatives must not only provide suitable tree stocking and spacing for the Kirt land's warbler but also accommodate their spatial and temporal needs such as the size, chronology, and age diversity of stands. The Kirtland's warbler (Dendroica kirtlandii) is an Endangered Species that is only known to breed in young, jack pine (Pinus banksiana) habitat in northern Lower Michigan. This warbler migrates to the Bahamas where it winters in low, broadleaf scrub habitat. The known breeding population is censused annually and has averaged 205 males from 1971 through 1987. The breeding population has been remarkably stable, ranging between 200 and 216 males for 12 of the past 17 years. The Kirtland's warbler occupies dense, jack pine stands where trees are from 5 to 23 years old and from 1.7 to 5.0 m tall. Typically, this habitat has been regenerated naturally by serotinous seeding resulting from wildfires in jack pine on sandy, porous soil. In the past 2 decades, however, Kirtland's warblers have been found in naturally regenerated unburned jack pine and in densely stocked pine plantations. A paper presented at the Society of American Foresters Conference held at Minneapolis, Minnesota, on October 21, 1987. Research Wildlife Biologist, North Central Forest Experiment Station, 1992 Folwell Avenue, St. Paul, MN 55108. I will review and describe four general areas of Kirtland's warbler biology and management: (1) the habitat requirements of the Kirt land's warbler, (2) the demography of the Kirt land's warbler and the evidence for population regulation by habitat limitation, (3) a hypothesis of how geography of suitable habitat affects stand colonization success and duration of habitat occupancy, and (4) the management strategies and recommendations needed to meet Kirtland's warbler requirements for optimal spatial and temporal distribution of high quality habitat. KIRTLAND'S WARBLER HABITAT REQUIREMENTS The most obvious difference between occupied and unoccupied suitably aged jack pine habitat is the dense tree stocking of the stands used by Kirtland's warblers. Areas with less than 20 percent canopy cover rarely are used for breeding. Optimal habitat typically has more than 7,500 stems per hectare and between 35 and 65 percent canopy cover. Tree canopy cover is more useful for evaluating habitat quality than stocking frequency or stem density because it combines tree stocking, spacing, and height factors. In any stand, the stocking should have from 20 to 25 percent tree cover to have a good chance of occupancy. Plantations can be adequately stocked for Kirt land's warbler