Laura Erickson's For the Birds

(Recording of a Kirtland’s Warbler)

When I think of fires and birds, the one bird that always comes to mind is Kirtland’s Warbler–a handsome songbird that breeds only in a tiny area of the northern lower peninsula of Michigan. Kirtland’s Warbler nests on the ground under the bottom branches of jack pines. Once the trees grow to be 16 to 20 feet tall, the bottom branches start falling off, and the trees are no longer suitable for nesting. So this warbler depends of a constant supply of new jack pines.

But the only way jack pine seeds can germinate is after a fire. Jack pine cones stay tightly closed until they’re exposed to the extreme heat of fire, and then they only grow on soils that have been scorched recently. Forest fire management in Michigan through the early 1970’s reduced the jack pine stands, and inadvertently almost doomed the Kirtland’s Warbler. Fortunately, people discovered what was happening before it was too late, and now controlled burns keep a steady supply of jack pines the right size for nesting for this endangered species.

Unfortunately, suitable habitat wasn’t the only problem facing Kirtland’s Warbler. When cowbirds discovered Kirtland’s Warblers in the late 1800’s, nesting success for the Kirtland’s Warbler dropped dangerously. Cowbirds were never found in central Michigan before European settlers came and altered the entire continental environment. Cowbirds used to make their living following the American bison, eating seeds in manure and bugs kicked up by the bisons’ massive hooves. When white men exterminated the bison, they introduced domestic cattle at the same time, which cowbirds quickly adapted to, expanding their range through much of the continent.

Cowbirds have been living with most species of North American birds for millennia, and most birds have developed ways of dealing with this parasite. If a wren or catbird finds a cowbird egg in its nest, it punctures it and tosses it out. If a Yellow Warbler discovers an impostor egg, it covers up the whole nest with a new floor and starts to lay eggs all over. Some species simply have enough babies each year to offset the effect of some failed nests.

But Kirtland’s Warbler didn’t have the time or genetic diversity to evolve any strategies for dealing with this new problem, and the total population became precariously low. The Kirtland’s Warbler population is currently hovering around 200 pairs, and in order to protect them, managers monitor many of the nests and actively remove and destroy cowbird eggs. They also have a cowbird adult trapping program, which seems to at least be helping a bit.

Oddly enough, the first Kirtland’s Warbler was not found in Michigan, nor on its wintering grounds. In 1851, a male was shot and sent to the Smithsonian Institution by a Dr. Jared P. Kirtland on his farm just outside Cleveland, Ohio. That was the last Kirtland’s Warbler seen for 28 years, when another bird was found and collected on Andros Island in the Bahamas. And it wasn’t until 1903 that the bird was found on its nesting grounds.

Because the total population of Kirtland’s Warbler is so precarious, its nesting grounds are protected. But the government agencies that guard it do provide tours. They’ll take you close enough to get a good look through a spotting scope or binoculars, which isn’t close enough to take pictures, but they do sell photos and slides for a nominal charge. If you’re planning a trip through Michigan early this summer and would like to get a look at this rare and endangered species, drop me a line and I’ll put you in touch with the people who arrange tours. It’s well worth the effort to get a peek at this unique creature.

(Recording of a Kirtland’s Warbler)

This is Laura Erickson, and this program has been “For the Birds.”