The Crossbill Story: Part 4 —
By Tom Hahn
Last time we left off with the numerous red crossbills, especially Type 2s but also some Type 4s, on the east slope of the Cascades, near Naches, WA. These birds had stopped breeding by mid-autumn of 1988, despite the enormous ponderosa pine cone crop that had matured there in late summer. I had visited the Devils Table site a couple of times during autumn when weather and teaching schedule permitted, caught a few adults, and found them to be molting and in declining or regressed reproductive condition. I noted birds in flocks with little or no song.
In late January of 1989, I had a chance to get over there to try to see what was going on in winter. I was expecting “wintering” (non-breeding) birds, since I thought they had stopped breeding in the autumn because the ponderosa pine cones had opened and shed many of their seeds. A fellow finch aficionado, Bill Buttemer—who was a post-doc at the University of Washington and had done his doctoral work on wintering physiology and behavior of American goldfinches—came with me, and we started by looking around up near Fish Lake, where the crossbill numbers had declined the previous June despite the huge ponderosa cone crop. When we walked up the snow-covered Merry Canyon road near the town of Plain, WA, we found a mixture of Type 2 and 4 crossbills foraging on re-closed ponderosa pine cones. In fact, the cones seemed to have gotten wet, re-closed, and then frozen shut. Interestingly, there was a ton of socializing going on, with lots of excitement calls, aka “toops”, vigorous aggressive interactions between males including fluttery aerial fights, and some loud song, especially by the Type 2s. We decided to head to Devils Table to see if we could get my truck up to the field site in the snow. I don’t think I would have even considered trying this by myself, but with Bill and his extensive experience doing winter field work in Michigan, it seemed a little less foolhardy.
We arrived in Naches after dark, headed up highway 410 toward the town of Nile, and from there up the paved but snow-packed forest service road, Bethel Ridge Road, that goes along Rattlesnake Creek toward Devils Table, Meeks Table, and trailheads into the William O. Douglas Wilderness. Partway up we came to a big pile of snow in the road where plowing had stopped. The road was only supposed to be open to snow machines and snowshoes or skis from there on. But…there hadn’t been any new snow in a while, and all the snow machine traffic had created a very nice hard-packed surface beyond the end of the plowed stretch, and a way around the snow pile wide enough for a vehicle. We slipped my truck around the side of the snow pile and proceeded without mishap along the snow machine-packed road to the little cutoff road up to the field site.
There, things looked pretty grim for continued vehicle travel. The snow on the spur road was up to the doors. We decided to go for it and see what would happen, figuring optimistically that if we got stuck we would just chain up (we had chains for all four wheels….might have been a good idea to put them on first!). We put the truck in 4-low and crawled – on pins and needles the whole time – the half-mile up to the field site. Thankfully, the snow wasn’t so deep and was much firmer when we got onto the more exposed ridge. It was a huge relief to park under some Doug-firs at my normal campsite. We pitched our tent in the snow, crawled into our sleeping bags, and went to sleep.
The morning of January 23 dawned clear, cold, and calm. We stayed in our sleeping bags and listened until about the start of civil twilight, around 7:00am at that location on that date, and heard the first Type 2s calling and tooping at 7:29. The only other birds around were some mountain chickadees until 7:42 when we heard some Type 4 Red Crossbills calling and singing a bit. We got our mist nets set up near the big ponderosa stumps that the birds liked to come down to, put our live decoys out—they had slept in their cage in the back of my truck, and the cold didn’t bother them at all since they had been living outside all winter—and in short order we started hearing lots of Type 2s and some Type 4s. The decoys were very excited and did their jobs well, luring in 19 Type 2 and three Type 4 over two days. The males had fully developed reproductive systems, the females had incubation patches, and we also found nests. My summary notes at the end of the day included: “Tremendous singing activity today, particularly by Type 2 birds. Lots of “moth flights.” Attempted copulations.” (Moth flights are the slow-wingbeat song flights that many male Cardueline finches, including crossbills, do during breeding.)
This was one of a few real “holy s#%t” moments I’ve experienced as a biologist. First, we saw that these birds were indeed breeding in early winter—you can read about something but still be blown away by the reality of it when you encounter it in person. And second, because they were doing it at the same location, using the same cone crop as the one they had stopped breeding in back in the fall! The cones in fall would only have had more seeds than they did now, and the days would have been longer, and the weather more clement, and yet the birds had stopped breeding then – even collapsed their reproductive physiology – but were breeding again now. In short, what appeared to have happened was that the birds had bred in the summer, ceased breeding and ended reproductive competence while they completed molt, and then re-acquired reproductive competence and resumed breeding by early winter, on the coldest, shortest days of the year, using the same cone crop as earlier. This experience gave me the first inkling that crossbills were not “infinitely flexible” in terms of reproductive timing, as the literature liberally asserted, but rather shared with other temperate zone songbirds an autumn reproductive hiatus (a reproductive refractory period that is widespread in temperate zone birds) that allowed them to complete the molt, which would be essential to long-term survival. So, yes, they were highly flexible, but fundamentally seasonal, like other temperate zone birds – a fascinating “variation on a theme of white-crowned sparrow,” rather than profoundly and fundamentally different, as my reading had led me to believe.
My field work that season left holes in the story, because the weather and my teaching schedule made it very difficult to get comprehensive data sets, particularly during autumn. In later years, I got more data from Type 2s that helped to fill in the picture, documenting much more thoroughly the collapse of the reproductive system in autumn despite a huge ponderosa cone crop, followed by subsequent resumption of extremely successful breeding in winter and early spring. This was in 2005-06 in the Warner Mountains northeast of Lakeview, OR, at a field site discovered by one of my graduate students, Rodd Kelsey, during a year that I was on sabbatical leave. Those Type 2s also bred during summer, terminated reproductive competence in autumn while they completed molt, and resumed breeding in winter, producing abundant fledglings in the spring.
This experience definitely made me start scratching my head about a lot of what was in the literature about crossbill reproductive timing, particularly references to “continuous breeding” from summer through autumn into winter and spring. A closer look at one of the main sources of that dogma – Bailey, Niedrach and Baily, 1953, “The Red Crossbills of Colorado” – revealed that they made statements about “breeding in every month” for which they provided no concrete documentation. What they actually did document was totally consistent with what I observed at Devils Table, WA, involving autumn termination of breeding while completing molt. It was pretty clear that they had found evidence of summer breeding and winter breeding, and had simply filled in the autumn months as also “breeding” since the birds were using the same ponderosa crop the entire time. After all, they assumed that if there were enough seeds present to support January nesting then there of course must have been enough to support November/December nesting as well, and therefore, that the birds must never have stopped breeding. Other sources proved equally fraught, as it turned out, suggesting to me that the “continuous year-round breeding” story about crossbills might simply be a myth, at least here in North America, rather than fact.
Still, this was my very first full field season, involved only Type 2s and a few Type 4s using only one type of conifer, ponderosa pine, and a lot of the seeds had in fact fallen out of the cones during late summer and early autumn. So I really wanted to see whether the pattern was consistent across western Red Crossbill types feeding on a variety of different conifer species and in different years.
To that end…next time, more about the crossbills west of the Cascade crest in Washington, including the San Juan Islands, and the humid coastal forests of the Olympic Peninsula.
UC-Davis professor and Finch Research Network board member Tom Hahn was around when the whole crossbill call type story started to get off the ground in the 1980’s.. This is the 4th part of the Crossbill Story. Tom has several more of these to share…..so stay tuned for more!
For Part 1 of the Crossbill Story — the Early Years, click here: https://finchnetwork.org/the-crossbill-story-the-early-years-2
For Part 2 of the Crossbill Story — Working with crossbills and the lightning bolt of Jeff Groth’s mind-blowing clarification of Call Types, click here: httpshttps://finchnetwork.org/the-crossbill-story-part-2
For Part 3 of the Crossbill Story — Big Ponderosa Pine Crops and More: https://finchnetwork.org/the-crossbill-story-part-3by-tom-hahn
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