About 10 miles outside of Mio, wildlife biologist Phil Huber pulls his United States Forest Service pickup truck over to the side of a gravel road in a scrubby flatland at the north end of Mack Lake Basin. The place, still recovering from an 800-acre fire in 1999, feels more prairie than forest. Yellow sedge and blueberry cover the ground. Sternum-high jack pine sparsely intersperse with spindly saplings of pin oak. Beside them rise the burnt skeletons of their predecessors.

The basin lies in the heart of the Kirtland’s breeding range, and today is May 25, the height of breeding time. Huber cups his hand to his ear and listens. “I hear a brown thrasher, a chipping sparrow, but no Kirtland’s,” he says.

But why not? The bird’s most important habitat pieces appear to be here. The jack pines are what the birds need for cover, and the trees attract the right insects for food—most notably the jack pine budworm. The sandy soil drains quickly so the ground nests won’t flood. Kirtland’s also like caterpillars drawn to pin oak, and they like the tree for perching, singing and scouting for intruders. The blueberries and other shrubby plants provide food and cover for ground nests. Even the black flies that swam in a thick cloud around Huber’s head are just more protein for the warblers and their babies.

“The conditions aren’t suitable here,” Huber says. His eyes scan the landscape. The jack pines at sternum height are maybe 6 inches or a foot too short for the Kirtland’s liking, and they’re spaced a little too far apart to provide adequate cover.

Huber climbs back in his truck and heads down the road again. Turning a corner, he drives past an area of lush jack pines that addresses both the height and density issues. The trees grow tall and thick, running right to the road in a 20-foot-high wall of green. Perfect Kirtland’s habitat here? Huber doesn’t even slow down. “After jack pines are 15 feet tall the Kirtland’s aren’t interested,” he says. Some researchers speculate there are fewer budworms as the trees age and less cover close to the ground. “We haven’t found a bird in these since 2000.” How, you might wonder, did this picky bird survive evolution?

To understand the Kirtland’s habitat needs, you first must understand the jack pine and what foresters call fire ecology. Contrary to 50 years of Smokey Bear admonishments, jack pines thrive by burning and regenerating after a fire. The needles of a jack pine contain nearly half the energy content, or BTU’s, of gasoline. So a mature jack pine forest, to anthropomorphize a bit, is standing there praying for a lightning strike or a match. When the spark comes, the forest bursts into flames, and, fanned by spring winds—the forest is most combustible in late April and early May, coincidentally just days before the Kirtland’s arrives North—it wipes out any competing species that have sprouted during the jack pine forest’s few decades of growth. Then before other species can get established, the tree rapidly reseeds and swiftly matures. It’s among the fastest maturing of native pines.

Expanding on the survival strategy at his next stop, Huber spreads the supple limb of a young jack pine to reveal a rose-purple bud with the size and suppleness of a gummy bear. He rolls it gently between his thumb and forefinger. “Most pines don’t produce cones until 25 years or even more,” he says. “But the jack pine produces cones at three years.” What’s more, the cone holds the seeds safe for decades (half are still viable after 20 years in the cone), not opening until temperatures of about 140 F melt the resin that holds the cone closed.

At some point after the last ice age the jack pines became established in Northern Michigan, and the Kirtland’s warbler established its remarkable synchronicity. The forest burned with regularity, though not all at once, so there were always stands of jack pine in various stages of maturity—most importantly in the range of 5 to 15 years.

So what was it that took the Kirtland’s—first described in 1851—to the brink of extinction, with just 167 pairs at the lowest points in 1974 and 1987? Perhaps the mention of Smokey Bear above tipped you off. When the policy of fire suppression took hold in the 1930’s, the number of acres of jack pine that burned each year plummeted. With far fewer acres burning, far fewer jack pines existed in that magical 5-to-15-year age range. As implausible as it sounds, even though jack pines grew by the millions, the remarkably specific habitat that the Kirtland’s needed was vanishing simply because the trees became too old. The bird was like a fish in a desert.

The lack of fire and resulting dearth of young jack pines was recognized as a key problem in the first Kirtland’s management plan, which the United States Forest Service put out back in 1962. Biologists reported that in the 15 years from 1911 through 1925, 146,000 acres of jack pine burned, but from 1946 though 1961 only 3,000 acres burned.

The state and federal governments began planting jack pines, but did so based on hunches and rudimentary research, and the results were strictly okay. Then a tragic fire in 1980 ended up greatly furthering the understanding of the Kirtland’s needs. On May 5 of that year, the Forest Service set out to burn some jack pine slash—residuals from logging—to prepare to replant more jack pine for Kirtland’s habitat. But a strong wind suddenly rose, and the fire surged out of control. Within just three and a half hours, the blaze had raced 7.5 miles. Before firefighters stopped the burn, it killed a firefighter, destroyed 44 homes and burned 24,000 acres. The amount of energy released by the high-BTU trees was equal to nine times the energy released by the atom bomb dropped on Hiroshima.

Biologists, most notably Dr. Burton Barnes at the University of Michigan, saw in the tragedy an opportunity to study Kirtland’s populations in a natural environment as the vast burn area regenerated. Barnes and his research colleagues wanted the answers to basic questions: How old were the trees when the Kirtland’s began to nest among them? What other conditions existed in the forest at that same time? When did the Kirtland’s stop using the trees? Dr. Carol Bocetti, who heads the Kirtland’s Warbler Recovery Team from her office at California University of Pennsylvania, spent three years of dissertation research looking at differences between planted jack pine stands and naturally regenerated stands. One example: did it matter if the lowest branch of the tree was more than 20 inches off the ground. And if it did matter, why?

Slowly but steadily, the research findings zeroed in on the habitat demands of the fussy bird. Previously, foresters managed Kirtland’s habitat in 200-acre blocks sprinkled around the landscape. But the research showed the birds needed far larger stands of same-age trees. Now, on national forest lands, trees are planted in up to 550-acre blocks, and state-land plantings can cover 1,000 acres or more. Also early stands incorporated 1-acre-square openings, because biologists knew the birds liked openings near their nests. But Bocetti’s research showed that opening edge was critical—she found 47 of 51 nests were within one meter of the  edge. Managers changed the shape of the openings to hourglass, made them one-quarter acre and increased their number to one per acre.

The 1980 Mack Lake Fire research also provided clear evidence about the age of trees the birds needed. “We found the first birds in there in 1986, a peak in population in 1994 and just two birds in 2000,” Huber says. The lesson: a stand of jack pines provides prime habitat for only 10 years. Today, to keep enough jack pine in prime Kirtland’s habitat, foresters manage nearly 200,000 acres in the jack pine plains of Northern Lower Michigan. As the recovery team revises the warbler’s recovery plan in coming years, the number of acres is likely to increase based on what science has discovered.

Photo(s) by Lou George FWS