Left-handed Crossbills?
White-winged Crossbills Loxia leucoptera, Homer, 18 February 2009.
Right now is a good time to be a crossbill on the Kenai peninsula. Spruce trees are heavy with cones and White-wings are very common. Reds less so, but there are a few around. I photographed these White-winged Crossbills in our yard in Homer this afternoon.
Do all crossbill lower mandibles veer to the left or are some “right handed”?
February 18th, 2009 at 6:41 pm
Wow, great photo of a male White-winged Crossbill! I know I will definitely be bookmarking this site for future reference.
March 7th, 2009 at 6:17 pm
I’m pleased to be able to answer my own question. I recently discovered this very interesting paper:
Benkman, C. W. 1996. Are the ratios of bill crossing morphs in crossbills the result of frequency-dependent selection? Evolutionary Ecology 10:119-126.
It turns out that both left and right-mandibled crossbills exist, and this paper hypothesizes that this serves a very important purpose.
The paper can be read and downloaded as a PDF here: http://www.uwyo.edu/benkman/ Click on the “Publications” link on the upper left of the page to find this and many other papers on crossbills.
Aaron Lang