South Hills Crossbill
A New North American Bird Species?
Photo courtesy of Craig Benkman
One does not expect to discover a bird species new to science while wandering around the continental United States. Nor does one expect that such a species would provide much insight into how co-evolutionary arms races promote speciation.
The South Hills and Albion Mountains of the Sawtooth National Forest of southern Idaho have a resident, Type 9, Red Crossbill that Craig Benkman describes as a good species, South Hills Crossbill Loxia sinesciuris. Sinescirius means "without squirrels". The South Hills area is surrounded by sage habitat, a natural barrier preventing emigration of pine squirrels. The absence of red squirrels enables Rocky Mountain lodgepole pines and crossbills to engage in a "co-evolutionary arms race" with the pines developing larger and thicker scales and crossbills evolving larger and deeper-based bills. A result is lodgepole pines' serotinous cones remain unopened until a fire sweeps through melting the cone scales. Without fire or squirrels, tightly closed scales surrounding lodgepole pine seeds are only opened by the seed predator, red crossbills.
There are two other crossbill types, Type 2 and Type 5, moving in and out of the area. Those two crossbill types have been recorded breeding with South Hills Crossbills in 12 of 1704 pairings, a frequency of 0.007, an order of magnitude less frequent than the hybridization occurring in other named European crossbill species. Sonograms of "South Hills Crossbill" flight call notes and songs are different than other "type" crossbill sonograms. Songs of South Hills Crossbills have many buzzy notes, whereas songs of both Type 2 and Type 5 crossbills consist mostly of shorter whistled notes. The authors suspect this new "species" also occurs north and east of the currently described range.
Scientific evidence seems to favor Type 9 Red Crossbills becoming South Hills Crossbill, but we will wait to see if the AOU Check-list Committee feels the same way. On a global warming note, climate change predictions have forecast the South Hills and Albion pine forests to disappear by the end of the 21st Century and with it this unique crossbill.
The March 2009 issue of Condor includes: Benkman, C., J.W. Smith, et. al. (2009)
"A new species of red crossbill (Fringillidae: Loxia) from Idaho." Condor 111: 169-176.
Prairie Falcon Audubon Observes the South Hills Crossbill
Prairie Falcon Audubon members took a very interesting field trip to the South Hills on July 30th, to observe the Red "South Hills" Crossbill. Lenny Santisteben and Patrick Keenan led a tour of their research station. Lenny, a graduate student at New Mexico State University has spent the last four summers in the South Hills collecting data on crossbills. He will publish his data later this year and present evidence that the Red Crossbills living in the South Hills are actually a new species, genetically distinct from other Red Crossbills.
The South Hills Crossbill, as many people refer to them, are unique in several ways. Many of their vocalizations are distinct from other crossbills. Unlike almost all other populations of Red Crossbills, the South Hills Crossbill is not nomadic. While other populations migrate many miles to find abundant sources of food, the South Hills Crossbill stays only in the South Hills and Albion mountains year round. Also, less than one percent of South Hills Crossbills hybridize with other crossbills.
The Lodgepole Pine and their pinecones in the South Hills are also unique. The nuts from these pinecones are the Crossbills’ main food source and are likely the reason the South Hills population of crossbills exist. Lenny hypothesizes that the crossbills and lodgepoles have evolved together in a sort of arms race, with the cones becoming increasingly armored and the Crossbill’s beak adapting to continue opening them.
On our field trip we observed crossbills being mist-netted (along with a Plumbeous Vireo, Green-tailed Towhee, and several Pine Siskins). We observed Pat measure, weigh, band, and release the birds. He required complete silence from our rather large group as he recorded the released birds alarm call as it flew back into the Lodgepole Pine forest. We also observed a well camouflaged Crossbill nest high in a pine tree.
This field trip boldly demonstrated how unique the South Hills ecosystem is and that it truly is an Important Bird Area. What other unique species or genetically distinct populations are flying, crawling, swimming or growing around southern Idaho, waiting to be discovered by an observant naturalist? Our group will closely follow the continued analysis of Lenny and Pat's data which could eventually culminate in the naming of a new species of bird, unique to our very own South Hills.
Want to hear the South Hills Crossbill? Check out the following links:
Global IBA Status for the South Hills
As the U.S. Partner for Bird Life International, Audubon has the responsibility for identifying and working to conserve a network of Important Bird Areas throughout the U.S. This network of sites is comprised of state level IBAs that are prioritized as continentally or globally significant by the U.S. IBA Committee, a panel of nationally recognized bird experts.
Photo courtesy of Craig Benkman
The designation means that the South Hills has been recognized as one of a relatively small group of sites that are of highest conservation priority. So far there are ~180 IBAs in the country (out of more than 2,100 identified IBAs) that have received this designation - 8 of which are in Idaho. The South Hills qualified as a Global IBA primarily because of its importance to breeding Sage-grouse (literally, the number of sage-grouse detected at leks within the IBA). It may qualify for other high priority species as well; we just didn't have the data available to determine that.
How will it help? That's a good question...one that I'm not sure I can answer quite yet. National Audubon is still really focused on IBA identification and classification, so it may be a while before we know where they are headed with this. They are starting to develop a monitoring/assessment program for Global IBAs that will be piloted next spring. If all goes well, they are planning on putting on training sessions in each of the states for IBA stewards that want to monitor their IBAs. So if this goes through, you all will likely be one of the first people with an op-portunity to participate. In addition, any conservation grant opportunities that come down the pipeline through Audubon will likely be targeted at Global IBAs - which would put you all at an advantage for getting help at the South Hills.
For more information about the South Hills IBA, see the Site Profile on the national Audubon website.
AOU Votes to Leave South Hills Crossbill as Sub-Species For Now
In the spring of 2010, the American Ornithological Union (AOU) voted on a proposal to split the South Hills Crossbill from the other Red Crossbills. A majority vote would have confirmed the South Hills Crossbill as an individual species but the AOU vote was a tie at 5-5, so it remains a sub-species, at least for now. Below is an informative account of the AOU proposal that succinctly describes the unique situation of the South Hills Crossbill. The proposal is followed by a fascinating account of each voters reasoning that demonstrates the ambiguity of what makes a species unique. The local folks who know and love the South Hills, as well as the larger birding community, will continue to watch with interest as more data is produced and a definitive answer can be made about the South Hills Crossbill.
Download and read:
- AOU Proposal to list South Hills Crossbill as a new species (PDF)
- AOU Votes (with Comments) to keep South Hills Crossbill as sub-species (PDF)
Original documents can be found on the AOU's website for the Committee on Classification and Nomenclature (North & Middle America) at http://www.aou.org/committees/nacc/ under Proposals.
South Hills Crossbill Hotspots
For information about birding hotspots in the South Hills, please read "South Hills hotspots." Areas of particular note for seeing the South Hills Crosbill include:
