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Listening for the song of the crossbill

June 29, 2011

Patience and a good ear essential in studying elusive crossbills, which live, breed and sing in the canopy

By Barbara Clements

Having a conversation with Julie Smith is a stop and go affair. In mid-conversation, she’ll stop, and listen. And then pick up the thread without missing a beat.

Smith, an assistant professor of biology, and biology major Aaron Grossberg ’12, are picking their way on a muddy trail to a beach near La Push, Wash., a small town which clings a point of land on the Olympic Peninsula.

Each is carrying a sensitive directional microphone aimed at the canopy of a Sitka Spruce stand.

About 100 feet above the trail, a chit-chit-chit sound drifts down. It’s the call of a particular type of North American Crossbill-unglamorously named “call type 10.”

Predictably, the types range from one through ten, with type 10, the elusive bird over our head, having been described in scientific literature only 18 months ago.

“Wait, I think I hear it over there,” said Smith, stopping a conversation about the how wrens seem to be drowning out all the other calls in this forest – and directing her microphone, with a parabolic reflector attached, at the call. Both listen intently, mics at the ready.

After about a minute, the pair, satisfied they have captured a good sound track, turn off  their recorders and start up the conversation again.

“I know I should probably study something else,” said Smith.”But I just love these birds. They are unpredictable, they don’t breed at a given time, they are nomadic, so you can’t find them in one area, but they have a wonderful song, they are colorful…and they are non-traditional.”

Crossbills – a member of the finch family – get their name from their beaks, which cross at the tip, giving the bird the ability to extract seeds from closed conifer cones. Each bird might gobble up 1000s of the small seeds daily to maintain their high metabolism.

When the pairs are mating, the vermillion-clad males have what amounts to a sing-off to get the girl, whose feathers are a demure olive green. Then the female gets to work, with no help from the male, who follows her around singing to her – a big help, Smith notes wryly – as she builds a stick nest in the canopy. They breed at any time during the year, even in below freezing weather.

The songs the  males use during breeding seasons may be specific to the different call types of crossbills. Smith is studying whether the songs of call types differ and play a role in reproductively isolating the types of crossbills from each other.

The birds give a real-time insight into how species may develop, literally on the fly, as they exploit niches, food sources and only breed with the types of the same call, Smith said. The process, called speciation, is one of the most important questions posed in the field of evolutionary biology, yet, it’s not completely understood by biologists, Smith said

Also flitting around the canopy about 100 feet above is call type 3, a crossbill which feeds on Western Hemlock cones. The next step in Smith’s research requires bringing female crossbills into captivity to see how they respond to songs of different call types.

“I like giving students an opportunity to have an experience they may not have in a lab,” Smith said, as she and Grossberg picked their way down the muddy trail to the beach.

Once the songs are collected, Smith and her students,Grossberg and Kirsten Paasche ’13, will take the sounds, and deconstruct them and analyze them on a computer to quantify differences in the songs of the different call types.  This is technical, dry work. But Grossberg is thrilled at the opportunity.

“I just love being outdoors, and this gives you an appreciation for the overall research we’re doing and how all the pieces connect, how they all fit together,” he said. Scientific research, he’s learned, is 95 percent failure and 5 percent success. So there is a lot of slogging through data that may not mean much.

But when something clicks, the feeling is great, he said.

“I just love going after that challenge.”

The characteristic chit, chit sound was gone. Grossberg and Smith listen one more time before heading back down the trail. Today’s field work was a wrap. Time to get back to camp, set the alarm for 4 a.m., and begin waiting for the songs once again tomorrow.