The top of a Douglas Fir in my yard. It’s covered in cones! (Image: Brendan McGarry)
Have you ever noticed just how many cones large coniferous trees produce? The largest Douglas Fir in my yard dumps cones everywhere most years. It’s no wonder I find baby firs growing everywhere.
Under each scale in a Douglas Fir cone there is room for two seeds and each cone has many scales, close to fifty. Every mature tree produces hundreds if not thousands of cones each year. That’s a lot of seeds and seeds are bundles of energy, the major ingredients for a seedling to sprout, set roots, form relationships with the local soil flora, and with luck, continue to grow.
We animals, both human and more than human, know this and whether or not we want to admit it, we’re just getting led around by plants and their seeds. Relationships, between seed eater and seed creators, have developed countless times, the world over, and Douglas Firs and our other native conifers are no different. Even on the Hill you can find a species whose life history is almost entirely devoted to conifer seeds – the Red Crossbill, Loxia curvirostra.
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Most of the world’s 236 species of finches eat seeds with some focus, it’s a defining food for them. But no other finches do it quite like crossbills. It’s there in the name: crossbills use their hooked, crossed bills to pry apart the cones of a variety of conifers and retrieve the seeds within. Watching them wrenching apart cone scales is fascinating but somehow simultaneously makes me uncomfortable, like watching a contortionist do something I couldn’t dream of doing with my body. Of course, every single living organism is shaped by their diet and bird beaks offer a tremendous range of adaptations, but there is just something about crossed mandibles that looks like it shouldn’t work.
This is a winning strategy though, because where there are large coniferous forests, there are crossbills. Six species of crossbills are distributed across most of the Northern Hemisphere, but no other species trumps the huge range of Red Crossbills. Across Europe, Northern Asia, North America, and even parts of Northern Africa and Central America you can find Red Crossbills enjoying the bounties of cone bearing trees.
Male (left, red) and female (right, yellowish) Red Crossbills. (Image: Melissa McMasters via Flickr)
Unless you are a birder, there’s a strong chance you’ve never seen or even noticed Red Crossbills even if you’ve spent your life near towering conifers. There’s a reason for that – aside from needing to drink water, occasionally eat grit to help grind down those seeds, and balance their acidic diets with alkaline supplements like salt or bone, Red Crossbills are birds of the canopy. That’s where fresh cones are afterall.
Red Crossbills eating grit on a gravel road. (Image: James Halsch)
On the Hill, the best way to locate a crossbill is to spend time near coniferous trees with nearly ripe cones. This means that certain times of year are better than others and that local populations can swing dramatically from zero to hundreds because cone production has peaks and troughs just like any other fruit. Obviously spending time in the more forested areas of the Hill is your best bet, but I’ve noticed Red Crossbills all over the Hill, just by listening.
While you might rarely see a Red Crossbill on the ground, they like to talk, and once you know what they sound like, are hard to ignore. Right now, all across Western Washington we are inundated with them because Douglas Firs have a lot of cones ripening and it appears to be a good crop year. Crossbill calls, cheerful pit pits and zree zrees ring through the canopy most of the day.
The story doesn’t end there though. Those calls tell a story about Red Crossbill populations. As it happens, there are 11 different sub-populations, or ecotypes, flying with what appears to be a specific interest in certain conifer species. And we can tell them apart by their calls.
Around the Hill the most frequent flyers are Type 4. or Douglas Fir (Red) Crossbills. This makes sense because Douglas Firs are the dominant conifer in lowland Western Washington. However there are crossbills that appear to focus on Western Hemlocks (Type 3), Sitka Spruce (Type 10), and Ponderosa Pine (Type 2), which all can occur in our region, depending on the time of year, the season’s cone crop, and weather events.
Each ecotype have bills that are slightly smaller or larger for the task of opening the cones of their main food source and body size suited to the various ecologies they inhabit, but the key distinguisher between the ecotypes is their vocal differences. Bill size/body size varies enough to muddy the waters between the groups, let alone that their populations overlap and they aren’t complete obligates to a tree species. Like other finches, Pine Siskins for example, Red Crossbill ecotypes can have irruptive years, where they travel well outside their normal range in search of food. Others just sit still and rarely leave, particularly Red-Crossbills living closer to the Equator.
Turn the volume up, (way up, this was on my phone), on the video above to listen to a Red Crossbill’s incessant calls. Credit: Brendan McGarry
Humans are only just unlocking the mysteries of these birds and defining their populations. You’d not be wrong in wondering why these ecotypes aren’t considered separate species – the world of taxonomy is full of people who want to lump species together or pull them apart. Most of the Red Crossbill ecotypes, at least in North America overlap in range significantly and thus far there isn’t enough genetic different to call any of them separate species, let along subspecies (though there are some Red Crossbill populations elsewhere that are distinct enough to be considered so). Interestingly, the birds once called “Call Type 9,” were elevated to species level in 2017, when it was realized that the population of Red Crossbills living in isolated mountain ranges in Idaho did not move around seasonally. Because these mountain ranges had no squirrels, the crossbills had few competitors and the Cassia Crossbill, Loxia sinesciuris, had settled into a comfy little niche. (Once the species was officially separate, a lot of birders took trips to southern Idaho to check that one new bird off the list.)
Taxonomy aside, it should be clear by now that Red Crossbills do quite a few things differently, so it shouldn’t be a surprise that their breeding schemes are aberrant too. Food availability being the main driver for breeding seasons (and an important impetus for migration), Red Crossbills don’t breed until cone crops are maturing. In North America, that’s typically mid to late Summer and in a good year breeding can continue into early Fall. Then, in places where the previous year’s seeds are still available, birds may begin to nest again from January to April. This bizarre sounds scheme lets Red Crossbills take full advantage of fluctuations in their choice of food. (I have no knowledge or records to reference of Red Crossbills breeding on the Hill – it feels unlikely but possible in areas with decent forest cover. They undoubtedly did in the past.)
As it turns out, Red Crossbills eat other things, including insects, and as I said above, they don’t just focus on their one conifer species, they just seem to prefer them (we like boxes and putting things into them). Future research may even provide enough evidence to split off more ecotypes into separate species that all co-mingle and swirl about the continent, but don’t ever manage to swap genes because they don’t breed at quite the same time. No matter what the real story is, I think most of us can agree these enigmatic birds offer up a curious, but successful way of living.
And though most birds turn my head, Red Crossbill voices are most ear catching and welcome when they start breeding in July. Their trills, chips, and chirrups ring out on mornings when most songbird voices are starting to fade, at a time when I can’t help but feel depressed because it feels like all the birds are gone, the fires have started, and the days are already visibly shorter. Red Crossbills are an antidote to my summer doldrums, way up there, pulling out seed after seed in the canopy.
Great article, Brendan! I had no idea that they started breeding in July, so much later than most other birds, and that is why I don’t hear them until summer. Thanks for the info.
I’ll never be able to unhear that noise…lol
These are really fun to read. I hope you continue.
We watched Red Crossbills doing something cool last month. They had knocked hundreds of cones from a Douglas fir to the ground and were working on them there as well as on the tree but several birds picked up cones and flew with them back onto the tree to continue feeding. Had no idea they could carry something that substantial. We submitted video to eBird with that checklist.
That was an awesome read. I love our songbirds. Keep yer cats inside, folks!