Terrestrial Native Species and Habitat Restoration: Kirtland’s Warbler Cowbird Control Active
By 1971, 69% of Kirtland’s warbler (a rare songbird with a limited breeding range in southern Ontario and the Upper Peninsula of Michigan) nests were parasitized by Brown-headed Cowbirds (a parasitic brood bird native to the Great Plains), resulting in less than one young Kirtland’s warbler produced per nest. Cowbird trapping began in 1972, and parasitism rates were quickly reduced to around 6%. The cowbird-trapping program was both necessary and effective but was designed for a critically endangered and extremely isolated population, not the larger population of Kirtlands’s Warbler, spread across 1.5 million hectares, that exists today. Our project seeks to determine whether cowbird trapping can be reduced without harming the Kirtland’s Warbler population.
All cowbird traps located on the Michigan breeding grounds for the 2018 breeding season were closed. Point counts (250) were conducted at all known breeding sites in the Lower Peninsula and automated recording units (ARUs) were placed at a subset of 48 of those sites to evaluate cowbird abundance. One hundred thirty Kirtland’s warbler nests across 8 field sites were found and identified to determine Cowbird parasitism rates. Only a few cowbirds were found to have parasitized nests and were detected via counts and ARU’s; therefore, instead of standard statistical analyses, findings were simply summarized. Four of 514 warbler nests were parasitized and only 20 cowbirds were detected in the study area during surveys. This confirms that Kirtland’s warblers are not currently being harmed by the cessation of cowbird trapping.
Results indicate that the cowbird control program can at least temporarily be suspended, thereby reducing conservation reliance in the Kirtland’s warbler and freeing funds for other management. However, because we do not understand why cowbirds have declined in this region, continued cowbird management will be necessary. The Kirtland’s warbler is likely to be delisted within the next few months and Michigan Department of Natural Resources (MI DNR) will take over responsibility for managing cowbirds. USGS is currently working in collaboration with the U.S. Fish and Wildlife Service (USFWS) and MI DNR to develop a monitoring protocol that will be more cost-effective than the cowbird trapping program.
Publications
Cooper, N.W., Rushing, C.S. and Marra, P.P., 2019, Reducing the conservation reliance of the endangered Kirtland’s warbler through adaptive management: The Journal of Wildlife Management, v. 83, n. 6, pp. 1297-1305. (https://doi.org/10.1002/jwmg.21714).
Contributions
In the short-term, conservation funding can be saved because cowbird trapping is not currently necessary to protect Kirtland’s warblers. In the short- and long-term this reduces the conservation-reliance of the Kirtland’s warbler and helps to ensure their sustainability post-delisting. In the long-term, reduced expenditures will allow the MI DNR to spend important conservation dollars on other threatened and endangered species in the Great Lakes Region. The results also provide support for delisting of Kirtland’s warbler.
Partners
Smithsonian Migratory Bird Center (SMBC) scientists coordinated field research, analysis, and publication of results.
Below are partners associated with this project.
By 1971, 69% of Kirtland’s warbler (a rare songbird with a limited breeding range in southern Ontario and the Upper Peninsula of Michigan) nests were parasitized by Brown-headed Cowbirds (a parasitic brood bird native to the Great Plains), resulting in less than one young Kirtland’s warbler produced per nest. Cowbird trapping began in 1972, and parasitism rates were quickly reduced to around 6%. The cowbird-trapping program was both necessary and effective but was designed for a critically endangered and extremely isolated population, not the larger population of Kirtlands’s Warbler, spread across 1.5 million hectares, that exists today. Our project seeks to determine whether cowbird trapping can be reduced without harming the Kirtland’s Warbler population.
All cowbird traps located on the Michigan breeding grounds for the 2018 breeding season were closed. Point counts (250) were conducted at all known breeding sites in the Lower Peninsula and automated recording units (ARUs) were placed at a subset of 48 of those sites to evaluate cowbird abundance. One hundred thirty Kirtland’s warbler nests across 8 field sites were found and identified to determine Cowbird parasitism rates. Only a few cowbirds were found to have parasitized nests and were detected via counts and ARU’s; therefore, instead of standard statistical analyses, findings were simply summarized. Four of 514 warbler nests were parasitized and only 20 cowbirds were detected in the study area during surveys. This confirms that Kirtland’s warblers are not currently being harmed by the cessation of cowbird trapping.
Results indicate that the cowbird control program can at least temporarily be suspended, thereby reducing conservation reliance in the Kirtland’s warbler and freeing funds for other management. However, because we do not understand why cowbirds have declined in this region, continued cowbird management will be necessary. The Kirtland’s warbler is likely to be delisted within the next few months and Michigan Department of Natural Resources (MI DNR) will take over responsibility for managing cowbirds. USGS is currently working in collaboration with the U.S. Fish and Wildlife Service (USFWS) and MI DNR to develop a monitoring protocol that will be more cost-effective than the cowbird trapping program.
Publications
Cooper, N.W., Rushing, C.S. and Marra, P.P., 2019, Reducing the conservation reliance of the endangered Kirtland’s warbler through adaptive management: The Journal of Wildlife Management, v. 83, n. 6, pp. 1297-1305. (https://doi.org/10.1002/jwmg.21714).
Contributions
In the short-term, conservation funding can be saved because cowbird trapping is not currently necessary to protect Kirtland’s warblers. In the short- and long-term this reduces the conservation-reliance of the Kirtland’s warbler and helps to ensure their sustainability post-delisting. In the long-term, reduced expenditures will allow the MI DNR to spend important conservation dollars on other threatened and endangered species in the Great Lakes Region. The results also provide support for delisting of Kirtland’s warbler.
Partners
Smithsonian Migratory Bird Center (SMBC) scientists coordinated field research, analysis, and publication of results.
Below are partners associated with this project.