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than many of the smaller warblers that nest farther north; in fact, next to the yellow-breasted
chat, it is the largest warbler in North America.
Carol and colleagues think they have found the answer to this mystery. In the late 1980s,
they explored the Seney National Wildlife Refuge's vast acreage of jack pine forest on
Michigan's Upper Peninsula. They found lovely tracts of young jack pines, but the ground
cover and soil moisture were all wrong for Kirtland's homesteading. Thick mats of moss
covered the soaking-wet ground. Some high knolls did have the requisite blueberry and oth-
er shrubby ground species, but only in isolated pockets. The researchers were not surprised
to find the young jack pine stands void of Kirtland's warblers. More detailed surveys on the
distribution of very sandy soils farther north could support this conjecture with data showing
that although pines are available, the essential sandy, well-drained soils are themselves rare.
At this same time, Burton Barnes and his team of graduate students were studying potential
breeding areas of the Kirtland's warbler around Grayling and a few sites on the Upper Penin-
sula, documenting the specific features that the warbler seemed to prefer. Well-drained soils,
both glacial outwash and areas of former glacial cover, seemed to predict Kirtland's warbler
occupancy. More important to the bird's reproductive success may be Grayling sand or any
similar dry, sandy soil and good drainage under the ground nest. As it turns out, the jack pine
is the only tree tough enough to survive centuries of such depleted, dry soil conditions.
This toughness is epitomized even in the jack pine's cones. The next day in the grove, I
grabbed a few to examine more closely. The small spheres looked as if they had been glued
shut. Nature by design: jack pine cones are serotinous, a term used to describe seedholding
packets of plants that open only when triggered by fire. The cones can remain sealed for dec-
ades until a forest fire whips through a stand. The hot fire kills the mature trees but guarantees
rebirth: when the heat of the flames hits 50°C (122°F), the cones pop open, spill the pine nuts
in their protective shells, and reseed the charred earth. Nature's baton cues a new melody, for
which the Kirtland's warbler is so precisely tuned, a firebird suite.
Historically, naturally occurring wildfires swept through the region and shaped the distri-
bution and sizes of jack pine forests. In the nineteenth century, loggers came here in search
of the coveted old-growth white pine for its fine, knot-free building timber but ignored the
lowly jack. Intensive timbering ended in the 1880s after loggers pillaged the last stands of
old-growth white pine and eastern hemlock. Extensive burning continued, which likely in-
creased the range of the fire-adapted jack pine. This interlude, after the loggers cleared out
but before settlers came, may have been the golden age in modern times for the Kirtland's
warbler. The largest extent of jack pine habitat in Michigan probably existed between 1885
and 1900. After that, extensive fires either no longer occurred or diminished as human settle-
ments spread. As jack pine stands matured under fire-prevention schemes designed to protect
public and private property, the warblers, according to local and national surveys, went into
a steep decline. Smokey the Bear and other popular symbols of the time may have prevented
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