January 26, 2016
Thanks to student blogger, Max Witynski, for providing insight into the mystery of crossbill movements and giving tips on how to ID the different “types” of Red Crossbills that we may encounter.
On the first Saturday of every New Year, my family likes to hike at a place called Pine Hollow in Sauk County, Wisconsin. Our official reason for visiting Pine Hollow is to see the enormous icicles which grow from the overhanging sandstone cliffs in the winter, but we also enjoy the amazing birds that seem to turn up there consistently.
One year, we found a Winter Wren hopping along the mossy bank, somehow surviving at the northern limit of the species’ winter range. Another year we spotted a Northern Saw-whet Owl roosting quietly among the evergreen branches. My favorite experience, though, was discovering a flock of White-winged Crossbills feeding busily on the hemlock cones, sending down flurries of snowflakes and winged seeds as they moved from tree to tree calling softly to one another.
Seeing the crossbills, I wondered—as I often do when I encounter migratory birds—where their journey began and where they would go after flying out of my sight. For irruptive finch species like crossbills which can move three or more times in a calendar year, crisscrossing the continent in search of favored food items, these questions are particularly intriguing. Seeing a Red Crossbill earlier this winter at a cemetery near my house brought this question back into my mind, and I decided to do some reading to try to better understand the movements of these unpredictable birds.
Two recognized species of crossbill occur in North America: Red and White-winged Crossbills. However, there are ten varieties of Red Crossbills (referred to as “types”) which are associated with different conifer species and which produce slightly different call notes, distinguishable on a spectrogram (a visual representation of sound). The types also show morphological differences in size and beak shape (larger, heavier birds have larger, heavier bills to feed most efficiently on bigger cones), as well as differences in distribution: some types range across the continent, while others, such as type 9 from the South Hills of Idaho, have very small ranges. As of yet, scientists have not reached a consensus about whether the types constitute full species, subspecies, or something in between.
Crossbills specialize on seeds from various conifer species, and are normally found in the northern and western parts of North America where these species occur. But when cone crops fail in the Pacific Northwest, say, because of a drought, the birds are known to move great distances across the country in search of new sources of food. Occasionally they even show up at bird feeders in more southerly states where they are reported by FeederWatchers.
But is there any way for a FeederWatcher who sees a crossbill to know what type they are looking at, or where it might have come from? A traditional method would be to look at band recovery data, but unfortunately band recovery rates for crossbills, as for many species, are extremely low. According to the USGS Bird Banding Lab, 15,938 Red Crossbills have been banded in the United States since 1960. Of these, however, only 48 have been recaptured. This constitutes a 0.3 percent return rate. For White-winged Crossbills, the situation is even more dismal: of the 2,947 White-winged Crossbills banded in North America in the same time period, not a single one has been recovered! The chances of a bird in your yard being a banded individual are also extremely small.
However, this doesn’t mean that gaining some insight is impossible. The sounds crossbills make provide a reliable clue. Each of the Red Crossbill “types” can be identified based on a sonogram of its flight call, and this can be matched to a “core” range and an “irruptive” range for the type. For example, Type 3 Red Crossbills are traditionally associated with western hemlock in the Pacific Northwest, but they also show up frequently during irruption years in the Midwest and Northeast. The bird at the cemetery near my house was most likely a Type 3.
According to Matt Young at the Cornell Lab of Ornithology, even low-quality smartphone recordings can be used to assign individuals to their call type. Assigning a bird recorded in a particular place to a particular call type helps us to better understand the big picture of Red Crossbill movement and distribution in North America.
So, if you’re lucky enough to have a Red Crossbill visit your yard this winter, consider making a recording and sending it to Matt at email@example.com. He’ll likely be able to tell you what type of Red Crossbill you saw, and where that type is typically distributed in North America.
The movements of White-winged Crossbills like the ones I saw at Pine Hollow, however, remain mysterious. Until a banded bird is recovered or we develop technology capable of tracking birds across great distances, white-wings will continue to be enigmatic emissaries from the boreal forest, always surprising to discover and fun to wonder about.
Young, M. (2012, October 8). North American Red Crossbill Types: Status and Flight Call Identification.
Connor, J. (2009, April 15). An Enigma, Wrapped in a Riddle, Inside a Pine Cone?
Hochachka, W. (2011, August 02). Science at work: How many kinds of Red Crossbills are there, anyway?
USGS band recovery database
Robbins, Jr., S. D. “Red Crossbill” and “White-winged Crossbill.” Wisconsin Birdlife: Population and Distribution, Past and Present. Madison: University of Wisconsin Press, 1992. Print.
Max Witynski is a junior at Cornell University majoring in Biology and Society. He is interested in ecology and conservation biology and science communication. Max has also done research on bird-window collisions, migratory connectivity, and song recognition.