The population of male Kirtland's warbler (Dendroica kirtlandil) in the breeding season has averaged 206 from 1971 to 1987. The Kirtland's warbler 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 regenerated from wildfire or prescribed burning. The rest were in plantations (11 ~ or in 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 following harvest. From 1982 to 1987, suitable regenerating areas were barely sufficient to replace currently occupied maturing stands, so population growth was impeded. Ecosystems of suitable size and regeneration 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 suitable 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).

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SummaryKirtland's WarblerDendroica kirtlandiibreeds in young jack pinePinus banksianaforests on sandy soils in Michigan's lower peninsula, where there were 502 censused singing males in 1951 and 167 in 1974 and 1987. An ongoing control programme for the Brown-headed CowbirdMolothrus ater, a nest parasite, resulted in immediate and continued improvement in warbler reproductive success which was not, however, matched by an increase in warbler numbers until the 1990s. From three 1,000 ha reserves in the 1960s, currently over 54,000 ha are managed for the warbler. Despite the establishment of managed plantations, over 70% of warblers censused in the past 15 years have occupied habitat created by wildfires. Optimal habitat consists of more than 5,000 trees per hectare in a mosaic of dense patches interspersed with small openings. Nearly 70% of adult and 30% of juvenile warblers departing for the Bahamian wintering grounds return each spring, and the Michigan singing male population increased from 212 (1989) to 397 (1992) as abundant habitat, resulting from a 1980 wildfire, became available at Mack Lake. This suggests that lack of optimal habitat in Michigan has been the species's major problem.