Scientists evaluate evolution of crossbill’s beak, food source
HANSEN, Idaho – A team of scientists is evaluating a southern Idaho bird that one researcher believes is a prime example of a species evolving with its food source.
The South Hills crossbill has physically changed as its food, the lodgepole pine cone, has changed over the past several thousand years, Craig Benkman says.
He believes the evolution has reached the point that not only has the bird become a distinct species but possibly the only species in the country that does not leave the state where it is found.
The bird is distinguished by a large crossbill that lets it crack the pine cone for its seeds.
Over millennia, the lodgepole cone has become ever harder to crack to preserve the seeds for regeneration rather than food for the birds.
At the same period, Benkman said, the South Hills crossbill’s beak has become larger to handle the tougher cones.
“It’s like an arms race,” Benkman said.
“The trees have increased their defenses. The birds increase their offenses.”
Combined with the bird’s unique call, its preference to mate within its community and its inclination to stay put, Benkman and his research team hope to make a case for distinct species status to the scientific community in a paper later this year.
The designation would bring more attention to the bird and to southern Idaho’s South Hills area in the Sawtooth National Forest because that is the only place where the bird is found.
Benkman’s research team estimates 10,000 to 20,000 South Hills crossbills live in the area.
While other crossbills spend a season or a year in the South Hills before moving on, the native crossbills remain.
Because of the physical changes over thousands of years, Benkman said the birds are essentially trapped in the South Hills with their food, the lodgepole pine cone.
If an infestation of beetle or fire wiped out most of the lodgepole pines, he said, the crossbill population would also be destroyed.
“There’s no place to go,” Benkman said. “Their bills are too big.”