Tuesday, September 22, 2009

South Hills Crossbills

South Hills Crossbill male (Rather poor photo by Narca)

Dr. Craig Benkman, who gave the banquet keynote talk at Western Field Ornithologists' annual meeting in Boise, has researched the habits and vocalizations of Red Crossbills for years. His work is helping to untangle the confusing crossbill complex. Just how many species of Red Crossbill are there? What distinguishes them? Are we seeing an example of evolving species, and at what point are they sufficiently distinct to be considered separate species?

Benkman recently proposed a new crossbill species: the South Hills Crossbill, a sedentary species known from the South Hills and Albion Mountains of southern Idaho. For more information on his publications and research, go to his website:


Here is the gist of his talk:

Red Crossbills in North America are divided into 9 or 10 "types," first recognized by Jeff Groth. Each type has corresponding calls, songs, and seed preferences. These types specialize in foraging on particular species of conifer seeds, and the grooved palates of their bills match perfectly the size of the seeds they eat.

"Type 1" lives in the eastern US and only rarely feeds on hard pines like Ponderosa.
"Type 2" feeds mainly on Ponderosa Pine.
"Type 3" feeds on the small seeds of Western Hemlock.
"Type 4" specializes on the thin seeds of Douglas-fir and is small-billed.
"Type 5" eats the seeds of Lodgepole Pine.
"Type 6" feeds on seeds of pines from the Sierra Madre and southwestern Sky Islands, and is large-billed.
"Type 7" is probably a generalist.
"Type 8" specializes on seeds of Black Spruce.
"Type 9" is the South Hills Crossbill, a specialist on Lodgepole Pine.
"Type 10" has been proposed by Ken Irwin; it specializes on coastal Sitka Spruce.

So why is Type 9 distinct? Only in a small area of southern Idaho does Lodgepole Pine grow in the absence of tree squirrels. Squirrels harvest pine nuts very efficiently, and begin their feeding at the top of the cone, unlike crossbills. Where squirrels feed on pines, they drive the evolution of pine cone structure. These pine cones have developed thicker protective bracts, especially at the tops of the cones. Squirrels harvest whole cones early in the fall, and cache them for winter, making the seeds unavailable to crossbills. Because crossbills must forage on seeds remaining on the tree, their food supply is more erratic where squirrels share the habitat, and those crossbills must become nomads when they run out of food.

Tree squirrels have never managed to cross the surrounding expanses of sage to reach the Lodgepole Pines of the South Hills, and pine cones here do not show the adaptations to squirrel predation found in Lodgepole Pine from other areas. Without squirrels, the supply of pine cones is more reliable, and these crossbills can afford to be sedentary. South Hills Crossbills have evolved large bills to deal with the pine cones, as well as distinctive calls. Researchers have found a very low frequency of hybridization between South Hills Crossbills and other types, which occasionally occur here as well. Indeed the proposed name for this proposed species is Loxia sinesciuris, which translates as the crossbill without squirrels.

In addition to Dr. Benkman's talk, Nathan Pieplow ably moderated the sound identification panel, both of which prepared us very well for Sunday's field trip to the South Hills to look for the crossbills. Sound ID panelist Rich Hoyer described the Type 9 call as "DYUP." That phrase I could remember. If you would like to hear crossbill calls, go to this website and click on the arrow next to each entry's name:


You can also find more information on calls at Nathan Pieplow's website, www.earbirding.com.

Sunday morning we set out very early in vans, eventually winding our way up into the South Hills of Sawtooth National Forest. No sooner had we arrived at an upper campground near Porcupine Springs, than "Type 9" South Hills Crossbills flew into the Lodgepole Pines next to the parking area, DYUP-ing as they came. For an hour or more, small groups of crossbills arrived and departed, giving everyone exceptionally good views. Yes!!

If this split is accepted by the American Ornithologists Union, Idaho will have gained an endemic bird species.

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