For the Birds Radio Program: Kirtland's Warbler 2001 Census
One of the most hopeful environmental stories in a long time is this year’s census data for Kirtland’s Warbler. This endangered species nests only in the jack pine forests in the northern part of Michigan’s lower peninsula. Scientists started conducting a census of Kirtland’s Warblers in 1951, and have made the census an annual event since 1971. They count every single territorial male, which is a difficult task, but not at all impossible thanks to the openness of the habitat and the fact that this little warbler’s range is so restricted geographically. The worst years ever were 1974 and 1987, when only 167 males were found. This year marks the all-time high for the species, 1085 singing males, including several in the Upper Peninsula-all mated with females.
Kirtland’s Warbler is endangered because its habitat requirements are so very precise. It’s a ground nester, and nests only under jack pine branches. When jack pine trees get tall and lose their bottom branches, they are no longer suitable for Kirtland’s Warbler, so they’re only useful from the time they’re 4 years old until they’re about 20. But young jack pine trees are a scarce commodity except following a bum-jack pine cones can lay dormant on a forest floor for many years, until the intense heat of a forest fire opens them. Without fire, there are no jack pines.
And without young jack pines, there are no Kirtland’s Warblers. Once ornithologists and ecologists figured that out, it was easy to use controlled bums to manage large tracts of northern Michigan forest for Kirtland’s Warblers. One of the probable reasons the warblers have been recorded in the Upper Peninsula every year ever since 1996 is that back in the late 70s one bum went out of control, killing some people and destroying far more acres of land than the planners wanted. But thanks to all the production since then, in the 90s there ended up being more warblers than habitat within their normal range, and they started spreading out a bit. There have been a handful of records of Kirtland’s Warblers singing in Ontario and Douglas County, Wisconsin, but so far there’s been absolutely no evidence of females outside of Michigan.
As habitat problems started easing with heavy management, there was still a problem, because the habitat so perfect for the warbler was also great for a new bird on the Michigan scene-the Brown-headed Cowbird. In ‘1-e 1950s and 60s, so many Kirtland’s Warblers were raising baby cowbirds instead of warbler !that the prospects for its survival became very bleak. So people involved in the Kirtland’s Warbler recovery team started trapping cowbirds—a project that continues today.
The US Forest Service and the US Fish and Wildlife Service provide daily tours every year between about May 20 and July 2-they show a brief film about Kirtland’s Warbler first, and then take you to places where the birds are fairly easily seen, though they are very strict about keeping people on roads and wide paths, and away from nests. It’s harder to find the birds after the peak of their singing period, but not impossible to find them later in July. If you want to get there next year, the US Fish and Wildlife Service has a website where you can get more information.