In migration, fat is key to survival

Our friend at the Smithsonian Migratory Bird Center, Nathan Cooper, continues to make news with his various studies on the movements of Kirtland's Warblers on the landscape of both the breeding grounds and wintering grounds -- and now on everything in between.

A story published on Oct. 4 on the website of the SMBC features Cooper's latest research on KW movements, focusing on the impacts of particularly dry winters on the wintering grounds in The Bahamas and across the Caribbean. We knew that dry winters had a carry-over effect on nesting season -- that adults were less successful in raising young in the summers following dry winters. But Dr. Cooper's new research shows that dry winters have an impact in a different way: higher rates of mortality during spring migration.

We knew from earlier research that birds that arrive on the nesting grounds after dry winters are less healthy because they are carrying less fat. They need to spend more time gathering food for themselves, which means they have less time to dedicate to gathering food for their young. The result is fewer hatchlings successfully fledge.

But Dr. Cooper's research shows that those same birds that are carrying less fat when they decide to leave the wintering grounds are also more likely to perish on their migration. According to the Smithsonian's website, "The team analyzed three years of radio tracking data from 136 tagged (with radio transmitters) Kirtland’s warblers to estimate their survival rate across their migration and its relation to environmental factors."

This research is the result of a grant from the U.S Fish and Wildlife Service’s Great Lakes Restoration Act "to build full annual-cycle population models for Kirtland’s warblers." Building this model will help the Conservation Team identify specific dangers involved in migrations and potentially work to mitigate some of them. According to the Smithsonian's story, this model will help scientists determine how the dangers of migration fit into the broader picture for warblers. That information is potentially useful for the conservation of other declining migratory species.

You can read more here: https://nationalzoo.si.edu/.../drier-winter-habitat...

Cooper's study was published in the Oct. 4 issue of "Current Biology." (It's behind a paywall. Sorry.) https://www.cell.com/curre.../abstract/S0960-9822(24)01225-9

Five years later, lessons to embrace

Scott Hicks of the U.S. Fish and Wildlife Service at the 2019 celebration of the delisting of the Kirtland's Warbler. Photo by Jim Bull

On Oct. 9, 2019, a notice appeared in the Federal Register, the official journal of the U.S. Government, that announced that the Kirtland's Warbler was being removed from the federal Endangered Species List.

That morning, in an event held in East Lansing that was half ceremony-half celebration, many of the people who were and are responsible for the conservation of the bird gathered to say "Job well done." Even though it was self-congratulations, it was still well-deserved. Endangered species conservation doesn't often have a happy outcome. The Kirtland's Warbler is one of the rare stories of success.

An anniversary, even if it is just as short as five years, gives us a chance to pause and reflect, an opportunity to consider what we've done to achieve delisting and what worked and what's not since 2019.

In the years prior to delisting, we learned that we needed to understand the natural processes of the jack pine ecosystem to give the bird what it wants and needs. Since delisting, we've learned that the management that we're doing to benefit the bird is actually having a negative impact on the ecosystem as a whole: our management is helping the birds but is causing a decline in the biodiversity of the jack pine ecosystem. And just as scientists adapted jack pine management during the recovery period, they understand that this new challenge will force them to continue to adapt.

Perhaps the most important thing that we have learned is that we must continue to watch the warbler. Its actions and reactions to various conservation efforts will guide us in future decisions. In the words of Carol Bocetti, the long-time leader of the Recovery Team and Conservation Team says, "We have to continue to listen to the bird. The bird is always teaching us."

Of all the lessons that we've learned, perhaps that is the most important.

Caught in the act -- of migration

We were thrilled yesterday when we got a text from our friends at the Powdermill Avian Research Center in western Pennsylvania that contained only a photo and two words. The photo was of a hatch year Kirtland's Warbler being held by a bird bander, and the words were simple and direct: "So exciting!"

Exciting, indeed!

It seems like Kirtland's Warblers are traveling incognito these days. They are rarely seen in migration and even with the proliferation of Motus tags and towers they are rarely detected. So when one ends up in a bird bander's mist net someplace between the breeding grounds and the wintering grounds, it gives us a chance to marvel at the luck.

It doesn't surprise us, though, that a Kirtland's Warbler was found in the hills of western Pennsylvania. Fall migration for the Kirtland's Warbler tends to track more eastwardly than the spring migration. And a Kirtland's Warbler has been recorded here before. According to records, a Kirtland's Warbler was banded at Powdermill in September of 1971.

It also does not surprise us that this was a hatch-year bird. Younger birds tend to depart the breeding grounds before the older adults. They'll start heading south in the next couple of weeks and are usually gone by the second week of October.

Hopefully we'll be getting some more data on this particular bird from our friends at Powdermill. We hope to share that with you soon. In the meantime, safe travels little bird!