Crossed With a Purpose

By Bill Chaisson
Of a Feather
After 50 years of birdwatching without a lot of world travel, I don’t see a new bird very often. But this week I added a new species to my life list (which does not in fact exist anymore). Red crossbills are not particularly uncommon in the northeastern United States, but I have somehow avoided getting a good look at them. I don’t really count seeing flocks of them fly overheard, irregular self-propelled black bird-shaped objects against the sky, making their characteristic contact calls, as actually seeing a bird.

My wife and I had driven up to North Wilmot to walk the dog on a property with a conservation easement on it. The old farm sits at about 1,200 feet above sea level. In addition to the pasture land, it is mostly northern hardwood (maple-beech-birch) with patches of white pine and hemlock. It is not high enough for fir and spruce.

But the white pines are having a bumper crop of cones this year, a phenomenon that is widespread enough that it has been noted a couple of times on the NH Bird Forum. This is a quasi-cyclic event in the sense that many variables enter into the lightness or heaviness of cone production, and it varies from species to species. Fir and spruce are normally cyclic but the western white pine, at least, is not. According to a 1977 review by the Pacific Forest Research Centre (of British Columbia), cone cycles vary between 2 and 11 years long. The eastern white pine would seem to be similarly irregular.

The male cones of white pines release their pollen in the spring and fertilize the larger female cones, which then take 18-24 months to mature. Therefore, the mighty pine crop that we are seeing is, to some extent, the product of conditions of a year or two ago. What kind of year was 2021? It was, at the time, the hottest summer on record in New England and included a great deal of rain. Perhaps the pines were stressed?

I am dwelling on cone production because it is important to crossbills, who get their very name from an adaptation that opens conifer cones. When I saw all these white pine cones weighing down the branches, my first thought was “Will this attract finches?”

We were driving down the dirt road from the farm when I spotted a flock of birds to my left. As we reached an intersection, six of them dropped out of a pine and settled in the dirt and gravel and began to forage, apparently looking for older seeds, as this year’s cones are still tightly closed and bright green. Only one of these birds appeared to be an adult male, while another appeared to be a female and the other four were immature males. We stopped the car in the middle of the road and watched them through the front windshield—there is very little traffic in this part of Wilmot—as they picked up objects from the ground, manipulated them with their beaks and either swallowed or dropped them.

The adult male looked like he was smudged with red and dark gray, as if he had been drawn with art chalk and then rubbed. The wings were an even black or very dark gray, but the rest of the body was irregularly colored, which made the bird look slightly disheveled. The immature males were similar except that there was no red but olive-green and yellow instead. The immature female looked like a plain gray finch because she was in the process of molting (into Definitive Prebasic Molt).

All of them, of course, had the characteristic crossed mandibles. Very young juveniles do not yet have this feature and are streaked and may be mistaken for house finches, but while the young female we saw appeared smaller than the others, it had crossed mandibles. This adaptation is not constant across the enormous range of Loxia curvirostris. There are varyspecies in North America and Eurasia and the size and curvature of the mandibles vary greatly. The Dalat subspecies (meridionalis), a resident of central Vietnam, has the most massive bill. There are 11 ecotypes in North America (defined by their call notes) with Type 6 having the largest bill and Type 3 the smallest.

An article by Matt Simon in the September 2016 issue of Wired magazine examines the coevolution of the bill of one red crossbill population and the cone of the lodgepole pine in Idaho. As magazines for the general audience go, Wired is pretty good, but this article gives the reader the impression that evolution never happens without geographic isolation. In fact, this is called sympatric speciation, while the kind that Wired thinks is normal is called allopatric speciation.

Simon spoke with ecologist Craig Benkman who explained that crossbills flock together and wander all year and stay in touch with each other via characteristic calls. This is what isolates them. The more they “talk” only with each other, the more their calls drift away from sounding like those of other flocks. Hence the 11 different ecotypes. Simon never identifies which one he is writing about, but it may be the Cassia crossbill, now considered a separate species.

Crossbill ranges are divided into core and second occurrence and primary and second irruption zones. They are most common in their core occurrence zone and mostly likely to irrupt to their primary irruption range. We live in the secondary occurrence range of Types 1 and 2. Type 1 is most common in the central Appalachians. We live in the core zone of the “enigmatic” Type 7, the primary irruption zone of Type 3, and the secondary irruption zone of Type 10.

However, like all science, these classifications are in flux. Jay McGowan of Cornell Lab of Ornithology has proposed a Type 12, which would take the enigma out of Type 7, separating it from a western population with a similar call.