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Tuesday, February 13, 2007

All crossed up

I went up in the foothills west of Denver last Sunday on a mission- to try and find some cooperative Red Crossbills. I really like this species, but my stock of pics in this department, um, left something to be desired- usually I hear them flying over or see them way up in tree tops. My dad Jim and some other Cobirders had reported seeing cooperative birds at Genessee Mt. Park (up near the flying saucer house, for those of you who have headed west from Denver on I70.) So with my dad as my scout and guide, up we went.
After pulling off at the first picnic area, we were reconnoitering when a pair of Crossbills flew in and perched in a very nice bare-limbed tree, not to high, with great light on them, etc. Where was my camera? D'Oh!, still in my truck... Guess I should learn from the Boy Scouts and be prepared next time.
Anyway, the next couple of times cooperative birds perched I was ready, and finally got shots that I like with angles showing the namesake overlapping bill, which the bird uses to open pine cones.
The hidden crux of the matter was to figure out which subspecies of Red Crossbill these were. Luckily, my friend Nathan Pieplow helped me out by summarizing the occurrence of Red Crossbills in Colorado:
"... Type 2 is the ponderosa pine specialist, and Type 5 is the lodgepole and spruce-fir specialist. These are the common breeders in the state. Interestingly, they are probably indistingushable by physical characteristics, and extremely close to one another genetically, but remain vocally distinct despite broad sympatry. Type 4 is the Douglas-fir specialist, and it may breed in the state, but I believe it is more common in winter..."
So that should make it easy to figure them out, right? Well, they were in an area of mixed conifers, with ponderosa pine and Douglas fir both present. So, type 5 is probably safely ruled out. That leaves call notes and bill length as the separators for Type 2 and 4. The call notes sounded like what I frequently hear in the Colorado foothills, suggesting the more commonly occurring Type 2 birds instead of the irruptive Type 4s. Type 4 birds also have smaller bills, but I don't have a lot of experience judging bill size in crossbills. Luckily, one of the nation's top Red Crossbill researchers, Craig Benkman, lent me his opinion:
"...From the photos and habitat I strongly suspect these are type 2 and that if you spent a fair amount of time out there you would mostly see them foraging on ponderosa pine at this time because doug-fir in the interior tends to shed it seeds earlier in the year (more so than ponderosa pine in our region; type 2 were nesting while feeding on ponderosa pine near the CO/WY border just south of Laramie in March 2005). The bills are just too big for type 4..."
Why all the interest in which type of Red Crossbill? Well, for one it is just an interesting topic to me. Secondly, these birds have major potential to be split into at least 9 species and to figure out which are which, birders are going to really have to pay attention to habitat and call notes.
Anyway, scattered about this post are some of my favorites. Note the female bird "flossing" with a ponderosa needle below- a curious behavior that apparently is shared by many finch species.

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