At my house I’m accustomed to seeing goldfinches and purple finches show up at my feeders. So at first what I thought I saw one afternoon was just more of the same, but in that quick glance I realized something was different.

Although one of the birds had the red, unstreaked head and chest of a male purple finch, he was bigger and thicker-bodied. The bird next to him had an odd, orange-yellow mottled plumage – definitely not a female purple finch or female goldfinch.

This applied to a third bird with a dirty-yellow body and black wings. I looked at their beaks and that was the clincher. The lower mandible crossed under the upper mandible, so the tips of each did not meet. They were red crossbills – a mature male, a first-year male, and a female.

Crossbills are large finches with bills especially adept at opening pinecones to retrieve the nutritious seeds within. They can slide their bills in between a cone’s scale, pry it open, and extract the seed with their tongues. Crossbills do eat the seeds of other trees, and will eat insects during the warm months. However they rely primarily on the seeds of coniferous trees, and their bill shapes evolved so they could easily exploit this recourse.

Because of this, they are known as “nomads,” roaming widely in search of abundant cone crops. They are not “true” migrants in that they migrate regularly between breeding and wintering grounds, but instead travel whenever the local food source runs dry, breeding wherever they find abundance again. They have been known to breed in any month.

There are several types of red crossbills in North America, and each differs from the other according to bill size, body size, and call note. Larger birds with bigger bills feed on cones that are larger and tougher to open, such as those of pines; smaller-billed birds likewise feed on softer and smaller seed cones of spruces, firs, and hemlocks.

Besides the red crossbill, North America is also home to the white-winged crossbill. This finch does not actually have an entirely white wing; instead it sports two white bars on black wings, and otherwise has basically the same coloration as the red crossbill, with minor variations.

There must not have been a very good cone crop in the area, because the crossbills in my yard seemed glad to take advantage of my feeders, one of which held shelled sunflower seeds that they devoured. They only stayed two or three days in late May; then they were gone, hopefully to more fruitful grounds.

Chris Corio, a volunteer at Fields Pond Audubon Center in Holden, can be reached at fieldspond@juno.com