Diario de davems

I spent the week of June 7-11, 2021 counting Kirtland’s warblers (Setophaga kirtlandii) in northern Michigan. This bird, one of 119 species of New World warblers, was nearing extinction 50 years ago and nested only in a small area in northeastern Michigan. Kirtland’s warblers winter in The Bahamas, where they are not habitat-limited. Habitat changes from intensive forestry and fire suppression, along with nest-parasitism pressure from brown-headed cowbirds (Molothrus ater) had reduced the population of Kirtland’s warblers to about 167 pairs in 1974. Kirtland’s warblers prefer young (~5-15 year old) jack pine (Pinus banksiana) for breeding, nesting on the ground underneath or near the lowest branches of a jack pine at the edge of a clearing, well-hidden among the grasses (Poaceae) and lowbush blueberry (Vaccinium angustifolium). Since jack pines are practically worthless as lumber, forestry practices of the 20th century favored replacing jack pine with other, more valuable, trees. Fire suppression also limited jack pine recruitment, since the cones of the jack pine only release their seeds with the heat of a forest fire. Finally, brown-headed cowbirds lay their eggs in the nests of other birds, which then raise the cowbirds as their own and raise fewer of their own babies. Some species are able to defend their nests or recognize and reject the cowbird eggs, but Kirtland’s warblers do not.

Intensive management was required to bring the Kirtland’s warblers back from the brink of extinction, with a recovery plan first described in 1971. This included acquiring federal land for restoring young jack pine habitat, modifying fire suppression efforts, trapping of brown-headed cowbirds, exclusion of the public from Kirtland’s warbler habitat, and an annual census. Over time, this management has advanced into highly-engineered “warbler factories” of young jack pine habitat interspersed with diamond-shaped clearings. This design maximizes the number of warblers that can successfully breed in a given area. As the jack pines age past ~15 years old, few warblers can be found in these areas and some time beyond 20 years old, the areas are harvested for pulp and replanted.

By 2019, the recovery goal of at least 1000 pairs over each of 17 years was met (many of those years have had >2500 pairs), so Kirtlands’ warblers were “delisted” from Endangered to Near Threatened, and the annual census was changed to every-other-year. Paired with US Forest Service (USFS) personnel, I (Dave) and another volunteer participated in the 2021 census that was run out of the Oscoda, MI USFS office, covering 10-12 miles (total) of transects through thick cover over five mornings. Guided by GPS and compass, I marked ~168 (one more than the minimum ;-) singing males on the maps, over five days. Other team members similarly marked singing males on parallel transects, which were then compared at the end of the morning to get a conservative count by triangulation. I spotted and photographed several singing males and one nest, but only under conditions that would not perturb the census. Other areas of northern Michigan were similarly covered by other teams. In addition to meeting the recovery goal of >1000 breeding pairs, Kirtland’s warblers have expanded into Wisconsin, the Upper Peninsula of Michigan, and Ontario, Canada.

If you want to participate in the next Kirtland’s warbler census, you don’t have to have an advanced degree or even be a birder. Training to recognize the Kirtland’s warbler’s songs, and use of maps, GPS, and compass is all onsite. You just have to be willing to crash through and get torn up by brush and trees, stumble over stumps and slash and into holes, get pooped on by gypsy moth (Lymantria dispar) caterpillars, and donate blood to blackflies (Simuliidae), mosquitoes (Culicidae), and deer flies (Chrysops spp.). Don’t miss it in June, 2023.