Red Crossbill Type 3 Identified by Call

Red Crossbill Female
(Type 3 - Western Hemlock)

This post is following up from last week on the crossbills at the JFK Library in Boston. I very much wanted to share the details on how the red crossbill was identified as a Type 3 or Western Hemlock type. But first, why do we even care about red crossbill types? (Most of my information comes from this article on eBird by Cornell ornithologist Matt Young, so definitely check it out if you want more details.)

Scientists and birders have known that there is a wide range of beak and head morphology within red crossbills in North America. Some scientists have thought that this variation in morphology might indicate distinct subspecies of red crossbill. Then, 20 years ago Jeff Groth learned that different populations of red crossbills could be identified by unique flight calls. So we now recognize "types" of red crossbills, not with calipers and a bird-in-hand, but by ear. (To be fair audio recordings need to be analyzed to be certain of identification.)

There are currently 10 identifiable red crossbill types that can determined by call. Most of these reside in high altitude pine forests out west. Though Type 1, the Appalachian Crossbill resides in the mid to southern Appalachians and Type 8 is in Newfoundland. The wide spread cone crop failure this season has lead to a large irruption of boreal finches as they search for plentiful food. Some birds like the common redpoll (recently spotted in Nahanton Park) mostly move south, but the red crossbills can irrupt clear across the country.

Red Crossbill Female

(Type 3 - Western Hemlock)

Scientists are very curious about how to categorize a red crossbills. Are they a species, a species with subtypes, a group of species, or something else? As different red crossbill types have different beak morphologies (small - big) and preferred food sources (hemlock, spruce, pine) they already have variation in physical traits and ecological niches which may indicate separate species (bill size and food choice are probably linked as bigger heads and beaks can crack tougher pine cones). Birds of different call types tend to mate with others of the same type, even though they may overlap in range and form mixed flocks at times. This type-recognition for mating further supports the idea of separate species. But as Matt Young points out, it is not known if this barrier holds up during different conditions, such as irruption year migrations (which only happen every 5 years or so). Could these types represent the modern equivalent of Darwin's finches and be an example of evolution in action? Thus the importance of identifying red crossbill types and obtaining audio recordings.

I started blogging because I really wanted to share some of the audio recordings I made at Nahanton, so the idea of recording birds (all from my iPhone ) in the name of science was too much to resist! Besides I thought the additional identification challenge would be fun. I was just lucky that I was able to find a red crossbill when I went looking last week. Most of the time she was silent, then she gave a few of her flight calls right before she flew off, but I was able to catch a recording. Watch the movie to listen to her flight call. Between 4-8 seconds the cracking noises were actually being made by crossbills (red or white-winged) as they pry open the scales of pine cones.

As soon as I got home I sent the audio clip off to Matt Young at Cornell for analysis, but then decided I should try and do the analysis myself. So I opened the audio file with Raven Lite (free software from the Cornell Lab of Ornithology) to see the audiospectragram. The program plots the sound frequency on the y-axis and time on the x-axis, additionally, louder sounds appear darker. Then I zoomed in on a single call note so that I could see all the details very well. After comparing the spectrogram to The examples in Matt's article and read the descriptions and it was clearly a good example of a Type 3 red crossbill! The sharp down, up, down, is unambiguous. It was amazing to me that one short note (a tenth of a second) could contain so much detail, and yet birds easily can distinguish audio details on this time scale. I needed a computer.

Red Crossbill Type 3

Flight Call Spectrogram

The type 3, or western hemlock, red crossbills primarily live in the Pacific northwest but they are the majority of the red crossbill types that have been identified in Massachusetts this season. As the name implies their primary food is hemlock, though spruces will also do (the ones I found were in Japanese black pines). The second most common is type 10, Sitka spruce, is also from the Pacific northwest and prefers spruces, or in he east, white pines. Interestingly, both type 3 and 10 are the smaller beaked crossbills. There are also a few eBird records in the state for types 1 and 2, though none near Newton.  Our nearest red crossbills to Newton were found at Arnold Arboretum where both type 3 and type 10 red crossbills were identified. So keep your phone or camera (the audio from a movie also works) ready to record any red crossbills that come our way!