A bird’s bill can tell you a lot about the breadth of its diet. The strong, tapered bill of a Eurasian starling is a great tool for extracting insect larvae off leaves, grabbing grasshoppers and other insects, manipulating fruits, crushing seeds and probing in the ground for prey. Starlings can generally find food.

At the other extreme are red crossbills and white-winged crossbills. Their upper and lower bills cross like a pair of scissors. The bill serves well to separate adjacent scales of the cones of conifers. Once the scales are separated, the hard harpoon-like tongue of the crossbill extends to the base of a scale to extract a nutritious seed. This specialized tool does its job well but is poorly designed for foraging on other types of food.

As specialists on conifer seeds, crossbills live a vagabond existence. They travel in flocks broadly in search of rich cone crops. Once such a mother lode is found, the birds often nest. White-winged crossbills can breed in every month of the year.

Red crossbills are enigmatic as far as their taxonomy occurs. In North America, red crossbill types tend to occur in different parts of the country. The individuals in each type give a distinctive flight call. There are correlated bill shapes and sizes for some of these call types. Some ornithologists argue that we should recognize twelve species instead of one. The types do wander, always in search of a bumper crop of conifer cones.

From late summer in 2023 into the summer of this year, red crossbills appeared in southern Maine in large numbers. This influx was likely driven by the abundant pine cones of eastern white pine. The white pine cone crop was two to three times higher than normal peak years.

Glenn Hodgkins, Christine Murray, Camden Martin and Gary Jarvis studied this influx of red crossbills and published their findings in The Maine Natural History Observer. I’ll summarize their valuable findings here.

Identifying the call type of a red crossbill is a snap if you have a recording of the bird. The recording can be converted to a spectrogram, a graphical representation of the notes and frequencies of a call. Red crossbill calls are usually loud enough that a recording made with your phone is sufficient to identify the call type.

Type 12 red crossbills are the most common type in Maine. These birds have a medium-sized bill, well suited to the high diversity of conifers we have in Maine. These birds can extract seeds from small cones like those of eastern hemlock to massive eastern white pine cones.

The research team found evidence of two additional types during this invasion. Type 2 (ponderosa pine) red crossbills are centered in the Rocky Mountains westward into the Cascade Mountains of Washington and Oregon and the Sierra Nevada of California. This type is well known for eastward irruptions, extending as far as the Canadian Maritimes.

Type 4 (Douglas-fir) Red Crossbills are mainly found the Pacific Northwest where Douglas-fir cones are the major food source. These crossbills irrupt occasionally to the Rocky Mountains and even the western Great Lakes region. They rarely make it into the Northeast. However, they occurred in significant numbers in Maine over the study period. This irruption of Type 4 birds is the best irruption in the Northeast in at least 25 years.

Our understanding of red crossbill movements in Maine is surely in its infancy. Prior to 2023, only two type 2 records and one type 4 record existed in the eBird database for Maine. All three call types were present in late August 2023 in Auburn. Surely, with the ability to identify birds based on their call types, we will learn more about the movements of the different call types.

Type 12 red crossbills were confirmed as breeders in southern Maine in the summer and fall of 2023 while types 2, 4 and 12 were confirmed as breeders in the winter and spring of 2024.

The article in the Maine Natural History Observer has several excellent color photographs of the three types of red crossbills that occurred in Maine during the study and other photographs as well.

I urge you to consider becoming a member of the Maine Natural History Observatory. Membership is as little as $10 a year and you will get four issues of the Maine Natural History Observer with accessible natural history articles and moving essays. A membership gives you access to all back issues. Reading through those articles is a great winter-time activity.

Herb Wilson taught ornithology and other biology courses at Colby College. He welcomes reader comments and questions at whwilson@colby.edu