RELATING KIRTLANDS WARBLER POPULATION TO CHANGING LANDSCAPE COMPOSITION AND STRUCTURE

The population of male Kirtland's warbler (Dendroica kirtlandii) in th e breeding season has averaged 206 from 1971 to 1987. The Kirtland's w arbler occupies dense jack pine (Pinus banksiana) barrens from 5 to 23 years old and from 1.4 to 5.0 m high, formerly of wildfire origin. In 1984, 73% of the males censused were found in habitat naturally regen erated from wildfire or prescribed burning. The rest were in plantatio ns (11%) orin harvested, unburned jack pine stands stocked by natural regeneration (16%). Twenty-two percent (630 of 2,886) of the Kirtland' s warbler males counted in the annual censuses from 1971 through 1984 were found in 26 stands that were unburned and naturally regenerated f ollowing harvest. From 1982 to 1987, suitable regenerating areas were barely sufficient to replace currently occupied maturing stands, so po pulation growth was impeded. Ecosystems of suitable size and regenerat ion characteristics (wildfire and plantation) doubled in area by 1989. In response, the population of Kirtland's warblers increased from 167 to 398 males between 1987 and 1992, but they withdrew almost entirely from the unburned, unplanted barrens by 1989 when the area of more su itable regeneration types increased. Minimum (368 males) and maximum ( 542 males) population estimates for 1996 were calculated based on 1984 average density (1.9 males per 40 ha) and peak population in burns (2 .8 males per 40 ha).