They’re back. Crossbills were mostly absent from Maine last winter. I didn’t encounter a single one, even when I went looking for them in their favorite places. In early June, I started noticing a few. By July, I was hearing them all over the spruce forests west of Baxter State Park.
Crossbills are finches with a uniquely adapted bill. The tips cross, allowing the birds to extract seeds from conifer cones. They insert their bills between the cone scales and twist, opening a gap that allows the bird to reach the seed with its tongue.
Crossbills are notorious nomads. They wander until they find a good cone crop. Then they are likely to stay until they’ve devoured most of it, whereupon they leave, unlikely to return until a new crop of cones has matured.
Two species of crossbill live in North America. The white-winged crossbill is spread throughout Canada, and its range often dips into the northern states, especially Maine. It has a smaller bill and dines primarily on the smaller cones of northern spruces. The red crossbill has a more southerly distribution, although it also relies on conifer cones. Some of these cones in the western states can be quite large, and some populations of red crossbill have evolved larger bills to deal with them.
But wait. There is now a third species, and therein lies the tale. Two years ago, biologists determined that one population of red crossbills was genetically distinct from all the rest, and it was declared to be a new species: the Cassia crossbill. Unlike other crossbills, this population does not wander. The birds are almost wholly confined to a small mountain range in southern Idaho. They have particularly large bills because they feed on the particularly large cones of lodgepole pines.
Until recently, the Cassia crossbill was considered to be just another type of red crossbill: Type 9. Red crossbills have been problematic for decades. Although they are all superficially similar, there is significant regional variation, and these have been lumped into 11 types.
Type 1 crossbills generally range along the length of the Appalachians. They have medium-sized bills suitable for the spruce, fir and pine typical of the eastern states. Type 1 wanders into Maine, but only occasionally.
By contrast, Type 2 crossbills have heavy bills capable of opening the cones of ponderosa pines throughout their home range in the west. They do wander east, especially into New York, but rarely as far as Maine. Type 4 has a medium-sized bill and is mostly at home in the Pacific Northwest, dining on Douglas fir. Like the others, it can wander all over the country, but rarely as far as Maine. Type 8 is confined almost entirely within its Newfoundland home range, where it prefers black spruce.
And so on. There is even a population that lives at the higher elevations of Central America from Mexico to Nicaragua — Type 11.
Type 10 seems to be the variation that most often takes up temporary residence in Maine. It is thought to be most at home among the Sitka spruces of the Pacific Northwest. It has a small- to medium-sized bill suitable for smaller cones. Therefore, it never wanders among the bigger cones of the Rockies, but it makes big incursions through the Great Lakes and into Maine.
Although all of these red crossbills are nearly identical, and they all make “jip-jip” calls while flying and sitting in treetops, the “jip-jips” of each type are slightly different from each other. By running the call through a computer and generating a sonogram — a graphic image that represents the song — biologists can identify which type has arrived in Maine. Birders are encouraged to record red crossbills and email the file to the Cornell Lab of Ornithology for analysis. It’s giving scientists the tools to better understand how distinct populations within a species evolve into new species. And all that is going on in Maine right now.
The white-winged and red crossbills are back. While up in the woods in late July, I heard big numbers of both around Nesowadnehunk Lake, though white-wings outnumbered red. Over by Umbazooksus Lake, the reds were more common. More recently, I heard white-winged crossbills in Lubec. And there is a pair of red crossbills that has been haunting the treetops of the spruces at Frazer Point on Schoodic Point in Acadia. I suspect they are romantically involved. She seems to think he’s just her Type. He thinks she’s a perfect 10.