Biology Reference
In-Depth Information
shaw, the dean of Kirtland's warbler biologists, had earlier estimated reproductive success to
be 0.8 fledglings per pair of adults per year. “So, in the absence of cowbird removal, I guess I
wouldn't expect success to go to zero, but the area could certainly become a population sink.”
The term Sarah used describes a state in which deaths exceed “recruitment,” or addition of
young to the population. And then there is the sad truth: cowbirds are nomadic, so removal
during one year has no bearing on the number of cowbirds that will arrive the following year.
Nest parasitism would rise again within a year or two and warbler numbers would dwindle if
biologists stopped the trapping program.
The first federal Kirtland's warbler recovery team, established in 1973, realized that for a
bird with such a limited range, it was essential to create more areas of suitable jack pine for
it to breed in. So, during the mid-1970s, the recovery team designated some 540 square kilo-
meters of jack pine stands, spanning state and national forests, for management as Kirtland's
warbler nesting habitat. Additional lands were added during the 1990s and in 2002 to bring
the total public land area specifically set aside for the Kirtland's warbler to more than 770
square kilometers. But how could these and even larger tracts of jack pines necessary to un-
derpin a recovery be maintained without burning huge areas, even some areas close to towns?
Silviculturalists from the USDA Forest Service argued that fire wasn't the only manage-
ment tool in the box. Logging practices and plantations could create conditions acceptable to
breeding warblers, they said. Ecologists were skeptical. In their view, forestry experts always
suggested logging and intensive management as the solution to any conservation problem.
The critical question was whether Kirtland's warblers would breed and survive as effectively
on plantations as in naturally burned forests.
Again, Carol Bocetti's dissertation work provided answers. “I found that plantations had
lower jack pine density and fewer openings in the managed forests than in natural wild-
fire areas,” she said. But, remarkably, she discovered that the critical response by the
warblers—measured by male density, clutch size, number of young fledged, and number of
parasitized nests—did not differ between plantations and fire-maintained habitat. It was all
about where the females were. Still, she recommended increasing both jack pine density and
the number of openings in future plantations, and managers have done so since then.
For a dedicated conservation biologist, a published paper is one reward. But the best out-
come is seeing one's research findings become management policy and then witnessing that
policy's positive effect in helping to save a species. “I think Carol's work shows that the log-
ging and replanting are effective in replicating fire-maintained habitat,” Sarah concluded. At
least for the Kirtland's warbler, Carol resolved the controversy through research. Almost all
Kirtland's habitat is harvested and replanted now, so there is very little variation in regen-
