It seems like we are constantly being bombarded with the dire news of melting ice caps and dying coral reefs. While so much of the natural world around us is being negatively impacted by the actions of humankind, it can be hard to find a win. Despite this, there are conservation success stories happening all around us.
In October 2019 the U.S. Fish and Wildlife Service announced the removal of a significant midwestern bird from the Endangered Species Act. To be listed under this act means that the species is in danger of extinction throughout all or a significant part of its range. This is not to be confused with the Federally Threatened Species List, which categorizes a species as one that is likely to become endangered in the foreseeable future in all or a significant portion of its range (U.S. Fish & Wildlife Service).
The Kirtland’s warbler was given limited federal protection under the Endangered Species Preservation Act in 1967 after their population was represented by a meagre 167 breeding pairs. It wasn’t until 1973 that the Endangered Species Act as we know it today was signed into law, making the Kirtland’s warbler one of the very first listed species. Their limited home range includes parts of Michigan, Wisconsin, and some of Ontario, Canada. As a migratory bird, they overwinter in the Bahamas. The Kirtland’s warbler is a small steel-grey coloured bird with a bright yellow chest and belly. The Kirtland’s warbler is a very habitat specific species, meaning it can only breed and survive in a very particular environment—one that is not all that common.
Nesting only in young jack pine forests, the warbler builds an open cup of grasses, sedges, and pine needles into a depression on the ground. Here they will lay 3-6 eggs, which will hatch about two weeks after nesting. Jack pine forests are widely distributed but not in large contiguous pieces, inhibiting an ideal environment for Kirtland’s nesting. Because they are ground-nesters, the Kirtland’s warbler prefers jack pine trees that are between 6 and 15 years old. Any younger, and the tree has yet to provide a substantial crown cover for their nests. Any older, and the lower, protective branches begin to die off, also no longer providing the necessary cover. Jack pines are also a fire dependent species. Without fire, the cones of this coniferous tree will not release their seeds, suppressing any new establishment of these preferred young pine trees. Like the Karner blue butterfly and its dependence on fire-dependent wild lupine, the Kirtland’s warbler needs fire disturbance to create a suitable habitat.
Not only is the warbler at odds with a vanishing habitat type, but they are also victims of a brood parasite, the brown-headed cowbird. This native bird species lays its eggs in the nests of other species to ensure their own young’s survival. Most nesting species will accept the cowbird’s eggs as their own, and then raise the chicks. However, cowbird chicks are much larger and stronger than the warbler’s young, ensuring that the cowbirds will outcompete and sometimes even push warbler chicks out of the nest. These cowbirds prefer open landscapes to densely wooded forests; therefore, restoring the warbler’s preferred habitat type will also limit population pressure from the cowbird.
As a part of the Kirtland’s warbler recovery plan, land management such as prescribed burns, clearcutting, replanting, and cowbird control are utilized on an annual basis. Management of the habitat ensures that the forest is regenerating at a rate that can sustain the specialist warbler species. Cowbird control has been an ongoing project for the last 40 years and has successfully brought down the rate of parasitized nests. Prior to this year’s delisting, only 1% of Kirtland’s warbler nests in the state of Michigan were reported to be parasitized by the cowbird. Since the warbler’s success, cowbird control has temporarily ceased.
While the warbler’s status has changed, the species will still receive special help and monitoring in order to avoid another population crash like before. Management agencies such as U.S. Fish & Wildlife and other state agencies will resume habitat restoration and cowbird trapping if the practices become necessary again. However, thanks to the collaborative team effort of like-minded conservation leaders, the Kirtland’s warbler is now at an estimated 2,000 breeding pairs, which is double the initial recovery goal!
What other species do you know of that have earned delisting status on the Federally Endangered Species List?
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