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Full-life cycle conservation: Kirtland's Warbler

The Kirtland’s warbler is our region’s rarest migratory songbird. There are approximately 2,000 pairs of this federally endangered species in existence and they breed exclusively on young jack pine habitat, primarily in several northern counties of the lower Peninsula of Michigan. While recent population trends are positive (average 6-7% population increases per year), the species is still very vulnerable, given its limited distribution, and the lack of knowledge about several facets of the species’ life cycle outside of the nesting season.

A Smithsonian researcher tracks fledgling Kirtland's Warblers using radio telemetry. Photo by Andy Forbes/USFWS.
A Smithsonian researcher tracks fledgling Kirtland's Warblers using radio telemetry. Photo by Andy Forbes/USFWS.

Currently, the wintering and migration biology of this species is poorly understood. Most observations of the species during the winter months have occurred in dry, scrubby habitat in the central Bahamas. However, the species has more recently been observed in different, pine-dominated habitats. Some preliminary data also suggest that at least some Kirtland’s warblers are overwintering in Cuba and Hispaniola. Whether or not these new discoveries are a result of wintering range expansion due to recent population increases, it is obviously important to gain a better understanding of the species’ wintering distribution, if we are to effectively continue to sustain its recovery.

Even less information exists about Kirtland’s warbler migration, other than a few dozen opportunistic sightings across the eastern United States. We don’t yet have a good understanding of what main routes most Kirtland’s warblers take to and from their breeding grounds, where their major stopover sites may be, or how long they stay at those sites. Since studies suggest that the majority of annual mortality (at least 50%) for this species likely occurs during the migration period, it is critical to learn more about Kirtland’s warbler migration biology, so that we can do a better job managing mortality during migration. For example, if the bulk of the Kirtland’s warbler population use the same migration route every year, stop at the same sites, and winter in the same relatively small area, then the species is more vulnerable to stochastic events such as storms, fires, etc. than if they are more spread out.

Finally, the period between leaving the nest and departing for migration (i.e., post-fledging) is almost completely unstudied in Kirtland’s warblers (and many other species). This is a very dangerous time for young birds, as they are highly vulnerable to predation due to their inexperience in avoiding predators and in finding enough food to survive. Also, research on other songbird species has indicated that both adults and juveniles may utilize different habitats during this post-breeding/pre-migration period, however this also is very poorly understood for this species. A better understanding of post-breeding habitat use and mortality of young Kirtland’s warblers may help identify new priorities for breeding ground management strategies that could help continue to turn the corner for this species.

In recognition of this glaring need, the Upper Mississippi River/Great Lakes Region Joint Venture is partnering with researchers at the Smithsonian Migratory Bird Center to conduct a new research effort to help address these knowledge gaps. Light-level geolocators are an amazing device that, when attached to a bird or other animal, enable researchers to determine the birds’ approximate latitude and longitude over time by recording ambient light-levels. This fairly new technology has helped us gain a wealth of new information about other bird species migration routes and wintering areas. Using a combination of wintering ground surveys, color-banding, radio-telemetry, and geolocators, Smithsonian researchers will help provide us with answers to many of these key questions which will help the U.S. Fish and Wildlife Service and our conservation partners better manage this unique species.

By Andy Forbes

Last updated: September 3, 2014