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Striving for Better

Better Knowledge • Better Understanding • Better Ways of Living • A Better World  

Crossbills feed on the seeds of lodgepole pine! Maybe you knew that. Maybe everyone knows that. But until fairly recently, I didn’t.

As someone who loves birds, watches them daily if possible, has conducted years of research on songbirds, taught classes on bird identification, led birding field trips, and even written about birds and ecology, I consider myself to be a bit knowledgeable about birds. I will never consider myself an expert because I know there is far more I don’t know about birds, and most topics, than I know now, or will ever know. But still, I like to think I know a few things.

And one thing I thought I knew about was crossbill feeding habits.

What is a Crossbill?

In case you don’t know, crossbills are a type of songbird distinguished and named for the unusual way the tips of their bill cross. This unique bill shape enables these robin-sized birds to pry seeds out of the cones of various conifer trees.

One of my clearest crossbill memories is tracking down a male bird diligently singing a long sweet melodious song one early August morning, in an old growth white spruce forest on the Kenai Peninsula of Alaska. I had been conducting surveys of breeding songbirds for the U.S. Forest Service there as part of a study of the effects of fire and forest succession. I had learned to recognize the songs of all the birds that had been singing that spring in all the different habitats where I had study plots.

But this was a song I didn’t instantly know. And it was late in the season for a bird to be singing. Most of the other birds—the warblers, thrushes, kinglets, and sparrows had already fledged their young and were no longer singing on territories. So I was excited to hear this bird’s song and eager to find it so I could learn its identity. Tracking the bird down wasn’t difficult. It was singing from the tip top of one of the tallest white spruce trees in the area. A quick view through my binoculars and I immediately recognized the medium-sized songbird, with its bright red plumage and stout, crossed-bill. It was not the first crossbill I had seen that summer by any means. But it was the first singing male I ever observed.

It was in ornithology class in college that I first learned about these crazy birds that may nest any time of year—including late summer, even fall or winter on occasion. Nearly all songbirds feed their young a diet of fat and protein-rich insects. So most songbirds time their nesting to coincide with the spring and early summer peak in insect availability. Crossbills, in contrast, feed their young the same food they consume as adults—conifer seeds. As a result, crossbills time their territorial singing and nesting to coincide with the availability of conifer seeds. In years with good cone crops, these birds can potentially nest about any time of year.

What is a Conifer, exactly?

Conifers are an ancient group of woody plants that rely on wind to pollinate their flowers and which bear their seeds in cones. Most people are familiar with pine cones. But there are many types of conifers that are not pines, but which also bear their seeds inside cones.

Douglas fir, subalpine fir, blue spruce, white spruce, and sitka spruce are examples of conifers in which I have observed both individuals and flocks of feeding crossbills. In central, southcentral, and southeastern Alaska. In the Yukon. In British Columbia. In Washington state. And in Colorado.

Nearly all my field observations, and whatever reading about crossbills I had done by then informed me that crossbills pry conifer seeds mainly out of the comparatively soft cones of spruce and fir trees. So, in my brain, crossbills were tightly associated with spruce and fir trees.

Lodgepole pines, in contrast to spruce and firs, have very tough cones, made up of thick bracts which are tightly sealed closed by pine sap. These cones are opened only by fire or intense heat. At least that is what I learned over and over from various classes, lectures, brochures, and interpretive displays. Lodgepole pines are a fire-adapted tree with “serotinous” cones that are opened only by fire or intense heat.

That is what I knew to be true. So I had not associated crossbills with lodgepole pine trees. Despite their remarkably-shaped and powerful bills, I never imagined that crossbills would waste their time trying to pry open the tough, tightly sealed cones of lodgepole pine.

So little did I know!

A friend enlightened me that scientists have found that crossbills and lodgepole pine trees are quite closely associated. I soon learned that the ties between these species is so tight that crossbills have differently-shaped bills in areas where isolated populations of lodgepole pine have somewhat differently-shaped cones! And crossbills do not just occasionally pry seeds out of tough lodgepole pine cones. In a large part of their range, crossbills are intrinsically tied to this particular tough-coned conifer species!

How did I NOT know that? Momentarily, I felt chagrined that I didn’t already know that. But then I was, like…Wow!! Cool!! I just learned something I didn’t know before! About an already amazing bird species that I love—about a common conifer—and about an important connection in nature. I realized that I needed to spend more time birding in lodgepole pine forests as I couldn’t recall ever having seen a crossbill in a lodgepole pine. And I immediately decided to read more about crossbills and lodgepole pines.

Thanks to google, it didn’t take long to find some fascinating articles about what scientists have recently learned about crossbills and lodgepole pines—and a curious inter-connection with red squirrels—which, I learned to my surprise, can also extract the seeds from tightly-sealed serotinous lodgepole pine cones. (See below to learn more.*)

This revelation about a bird I thought I already knew seemed like a good place to start my blog because it encapsulates a lot of what I want to share here.  I write with a strong dose of humility regarding what I personally do not yet know, or may actually “know” incorrectly, and what science and scientists do not yet know.

But I am on a quest to continually ask questions, learn more, and discover more.

I am fascinated by the remarkable diversity of amazing creatures with whom we share this planet and have a deep desire to seek greater understanding and appreciation of the ways that plants, animals (including humans), and microbes coexist now, and can hopefully survive together far into the future.

I invite you to join me in an uncharted, winding quest toward greater knowledge, appreciation, and understanding of nature, and in pursuit of better ways of living on our planet.

I know that I still have a lot to learn. How about you?

 

A Footnote

Just in case you’d like to know more about the connections between crossbills and lodgepole pine—here is a quick synopsis of what I now understand. There is not just one kind of lodgepole pine as I previously assumed. Actually four different subspecies are now recognized—some of these bear cones that are never serotinous and some bear cones that are sometimes, but not always, serotinous. The degree of serotiny in the lodgepole subspecies that bear serotinous cones is, at least partially, determined by the level of pine cone harvesting by red squirrels.

Where squirrels are abundant, serotinous lodgepole pines become scarce over time, since the squirrels collect and eat most of the seeds in the serotinous cones. Lodgepole trees that drop their seeds soon after they ripen are more successful reproducing where squirrels are abundant, so over time these become more common in such areas.

In contrast, where red squirrels are scarce or absent, lodgepole trees bearing serotinous cones become more dominant. In these lodgepole forests, the treetops are full of tightly-sealed serotinous cones that contain millions of tiny seeds—there for the taking if you happen to be a crossbill with a powerful enough beak to extract them. Red crossbills are able to find enough food year-round to survive and nest in such forests.

Quite remarkably, the lodgepole trees and red crossbills in one particular area seem to be affecting each other. The trees in this area have exceptionally tough pine cones and the associated crossbills have exceptionally large and powerful bills. These enable the birds to pry open even the largest and toughest of the trees’ serotinous cones.

The scientist who discovered these extraordinary crossbills proposed that these birds are an entirely new and separate crossbill species. The American Ornithologists’ Union recognized it as a separate species in 2017.

Interested to know more? Here are a couple of sources where you can read more:

https://www.allaboutbirds.org/guide/Red_Crossbill/overview

http://www.uwyo.edu/benkman/pdfs%20of%20papers/benkman_et_al_2009.pdf

https://ornithologi.com/2018/03/05/idahos-endemic-the-cassia-crossbill-loxia-sinesciuris/

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