The Crossbill Story: Part 3
By Tom Hahn
Last time, I blathered about gradually figuring out that there were different crossbill call types, and finally starting to have some success catching them. That got us up to the spring of 1988, my second year in graduate school at the University of Washington.
The winter/spring of 1988 was the tail end of the huge 1987-88 Douglas-fir cone crop at mid-elevations on the eastern slope of the Washington Cascades, and there were thousands of Red Crossbills in the area I spent most of my field time – the Wenatchee National Forest around Fish Lake and Lake Wenatchee. I remember first hearing the mellow dropping calls of a flock of Type 2s in March that year when I was netting at one of my standard sites near Fish Lake and being struck by just how different they sounded from the Type 3, 4 and 5 that I had been encountering. All of these types seemed to be using the abundant Douglas-fir cones. It’s a phenomenon we’ve observed repeatedly over the years; mature and especially open Doug-fir cones can be a great resource for all of the crossbill types.
As the spring progressed, I tried to settle on some possible places to focus my field work for the coming summer and fall. One thing that was clear was that ponderosa pine was in the process of making an enormous cone crop in the same areas that had the huge Doug-fir crop during the past year. Type 2s were already around in numbers, using the remains of the Doug-fir cone crop, and I remember in May, 1988, helping my friend Dennis Paulson with a birding field trip to the Cle Elum area (mid elevation east of the Cascade crest) and encountering a big flock of Type 2s coming to the ground for grit near the place we were staying.
I spent a lot of time out watching crossbills, and didn’t see them foraging much from cones in April and May. What they seemed to be eating the most were these little white waxy things that were all over the new growth tips emerging on the Doug-firs – one life stage of Cooley gall aphids, as it turned out. In late May, a big mob of Type 3s turned up right on the UW campus. I remember walking from the Zoology building over to the library and as I approached the door hearing a din of type 3 calls and what Matt Young would call “conversational song,” coming from a huge elm tree just outside the library door. There also were leaves raining down out of the tree and littering the ground – all of them ones that had been curled into tube-like structures by colonies of woolly aphids. The crossbills were plucking the leaf tubes off the twigs, scissoring open the rolled up tubes, and licking the aphid colonies out before dropping the leaf. These observations of crossbills eating Cooley gall aphids and woolly aphids were some of my first hints that insects were potentially really important to crossbills, at least at some times of year (more on this later).
In the area near Fish Lake, the developing ponderosa pine cone crop was legitimately phenomenal, and by late June and early July, Douglas-squirrels were already eating these new cones, peeling the scales off, consuming the seeds, and dropping the cone cores to the ground. Many of the branch tips had clumps of five or even six cones developing. Having read Bailey, Niedrach and Baley (1953), “The Red Crossbills of Colorado,” and absorbed their account of “Bent’s Crossbills” breeding copiously in the ponderosa forests of the Colorado Front Range, I thought the Fish Lake / Wenatchee area had to be an outstanding place for crossbills to settle to breed that summer. But as June turned to July, the numbers of crossbills in that area dwindled to almost zero. After a couple of trips where I only encountered one or two individuals in many hours of field time, I decided they really had left, despite the enormous developing cone crop.
Fortuitously, during a trip back to the Zoology department I ran into one of my committee members, Gordon Orians, and mentioned that the birds had mysteriously vanished from the Fish Lake area, and he said he had just come back from Meek’s Table, just east of Mt Rainier, and there had been lots of crossbills. This area is similar to the Fish Lake area but a hundred or so miles south. So I headed to that area and drove up one of the forest service roads that goes up Rattlesnake Creek near the town of Naches, WA (just west of Yakima) to a place called Devil’s Table. It’s a mixture of ponderosa, Doug-fir, grand fir, and a bit of western larch.
I remember getting out of my truck and putting my cage of crossbill decoys up on the roof of my truck cap, and within seconds they were all calling excitedly and a Type 2 male came sailing in doing a moth flight and singing loudly. There were hundreds of crossbills around, almost all Type 2, and over the next few weeks I found nests, mist netted dozens of them, and monitored their transition from breeding to plumage molt in late summer. One of the things that just blew me away was that these big Type 2s could actually open the immature ponderosa cones. Many of the trees had clusters of totally torn-up immature cones from which the birds had been extracting seeds. It was no mean feat – some individuals I netted appeared to have completely worn the feathers off one side of their face from pushing their heads well down into the cone along the basal cone scale they were prying up. I was hopeful that this huge ponderosa pine cone crop would be just what I was looking for to document crossbill physiological condition as they continued to breed (as I supposed they would) right through the autumn and into the winter, as others (e.g., Bailey et al., 1953) had claimed they did.
In September, the ponderosa cones opened and shed seeds copiously in the dry early autumn weather, and the crossbills seemed to be finished breeding. There were loads of juveniles around giving their “chitoo” begging calls. I had to be a teaching assistant in the fall, and I made several trips over to try to get data on molt and reproductive condition, but the drive was long, the weather was terrible, and I only got physiology and molt data from a few adults, but those few were not remaining in breeding condition. The birds were in flocks, and there was no evidence of further nesting after about the beginning of October. Singing activity had stopped. I figured they must have curtailed breeding because of the big ponderosa seedfall back in September – I was still in the mindset that crossbill annual schedules of breeding and movement were driven by facultative responses to food supply alone, and that termination of breeding in autumn had to be a direct response to declining food.
I didn’t expect to see any more breeding on that cone crop. Little did I suspect what I would discover when I returned to Devil’s Table a few weeks later, in January 1989. More on that spectacle in the next installment.
UC-Davis professor Tom Hahn was around when the whole crossbill call type story started to get off the ground. This is the 3rd 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
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