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Seeds, Nuts, and Red Crossbills

I was reminded of the squirrel, when I received an email from my birder friend David. I think you'll find what he says interesting.

He writes:

Last weekend I spent two days camping with my lads in southern Idaho. I went up to see the newly described form of the Red crossbill, the so-called South-hills crossbills, Loxia (curvirostra) sinesciuris, which is found only in two mountain ranges south and southeast of Twin Falls. The birds were easy to find, especially in the morning, and I got good views of their enlarged bills (not longer, but thicker, almost like the Parrot crossbills of Europe). They called and sang all around us, delightful even over the roar of the seemingly hundreds of ATVs there. Note that the photo found on most websites of this (sub)species shows a white patch behind the eye, which is NOT characteristic of the (sub)species, but is an anomaly of the one photographed individual bird. South Hills crossbills have become more differentiated than most other Red crossbill types in North America, and are excellent candidates for splitting out (though the AOU rejected splitting them this spring on a technicality).

You might want to check out the fascinating story of the South Hills Crossbill, which has recently been discovered in southern Idaho. To sum it up, Lodgepole pines are generally locked in an evolutionary arms race with Red squirrels (the very critters at your feeder), so they have evolved round cones that are hard for squirrels to bite down on (try biting on a tennis ball). However, in two low mountain ranges in southern Idaho (the Albion Mts and the South Hills), the squirrels are not present. So the Lodgepole pines there don't have to "worry" about their seeds being eaten by adorable varmints and have no selection toward round, ball-like cones. But Red crossbills, a "species" (probably many species actually, they are finding) found in the coniferous forests of North America and Eurasia, are highly nomadic and sometimes pass through the area. So THEY became the main consumer of Lodgepole pine seeds and thus created a different evolutionary pressure on that species. A new variety of pine thus evolved, altered by natural selection to have armored seeds in a manner that crossbills find difficult. It turns out, crossbills have bills very attuned to particular types of cones (Douglas fir, Montezuma pine, other pines, different firs & spruces...) and because the shape of the bill is so critical to obtaining food, the different varieties of crossbills don't seem to interbreed (thus the Red crossbill may actually represent up to 10 "cryptic" species in North America alone, hiding in plain sight. So, back to the South Hills: With the new types of cones, a new niche opened up for the crossbills passing through that area (types 2, 4, and 5, I believe), and some began to evolve larger bills to access the new, more elongated but armored cones found in these mountains. They became resident (since they became best fitted to these particular pines) and the new arms race was on. Now, both the crossbills and the pines are separate subspecies (at least).

So, now a new issue arises: Global Warming. It turns out that Lodgepole pines have evolved to take advantage of the nutrient bonanza and open sunshine created by forest fires. Their cones remain shut to hold onto the seeds locked within until the intense heat of a forest fire opens them up to release the seeds to start a new generation, phoenix-like, in the sun-lit ash. Some cones remain shut for over twenty years, it seems. Because the new cones are so tough to open, the South Hills crossbills are forced to eat seeds from cones which are several years old, after they start loosening enough to be pried open and after a nasty layer of protective resin has worn off. A researcher I had the happy fortune to encounter there last weekend (the patiently informative Julie Hart, who was a delight), said the crossbills generally go after the cones that are seven years old. However, with global warming, the cones are opening sooner, before the resin has worn off, and thus often dropping the seeds before the crossbills can get to them. It may not be entirely coincidental that the crossbill population has crashed in recent years (though bird populations relying on a specialized food source often fluctuate in cycles naturally--think snowy owls and lemmings). Some researchers have also predicted that the unique subspecies of Lodgepole pines, and the associated ecosystem, found in southern Idaho may become extinct by the end of this century (though I myself, with no credentials to back me up, find it improbable unless things get really bad--the pines appeared to be found over several hundred feet of altitude). It would be tragic if this dance, which has shaped two species into unique forms found nowhere else in the world, were to come to an untimely end because of some apes' unwillingness to change their lifestyles just a wee bit.

Isn't that a fascinating series of cause-and-effects? It's amazing the sorts of complex dramas that act themselves out before our unseeing eyes. Everything is so inter-related. What a planet!

The best place to see these birds is the Diamondfield Jack Recreation Area right on the main road into the South Hills. Conveniently, that is a campground with bathrooms.


 

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