Solving the Mystery of Songbird Migration

This June I had the privilege of helping out my friend and fellow lab mate, Allison Nelson, with her research project. She's studying the migration of hermit thrushes. Described by the Cornell Laboratory of Ornithology as an "unassuming bird with a lovely, melancholy song," these birds are well known for their beautiful metallic songs. Despite their popularity, the migration patterns of these birds are not well understood. Different populations with overlapping ranges travel in completely opposite directions - and we have no idea why. Allison aims to answer some of these questions.

To fund this research trip, Allison ran a successful Kickstarter campaign. Kickstarter is a crowd-funding website for creative projects where individuals donate funds at different levels in exchange for small gifts such as a picture or sound recording of a Big Basin hermit thrush.

With the money she raised through Kickstarter Allison was able to purchase 20 tiny geolocators that use light levels to determine the approximate latitude and longitude of the bird. The video below from her Kickstarter campaign describes out the aims of her study:

We spent a week in Big Basin Redwood State Park target netting hermit thrushes and harnessing them up with geolocators. Big Basin is California's oldest state park - the sites we were working in were full of lush trees and undergrowth.

The hermit thrushes here spend the summer in Big Basin and migrate south for the winter. They have high site fidelity, meaning they return to the same sites year after year. Allison color banded birds in Big Basin Park last year and we recaptured 9 of her birds from last year! That means those birds spent the summer of 2013 in Big Basin, flew all the way down to the southern United States or Mexico for winter, and then flew back to the exact same spot in Big Basin for summer of 2014.

Next year we'll return again to try to recapture the geolocator birds to download the data and see exactly where they spent the winter. Given our recapture rates from this year we're confident we'll get quite a few of the geolocators back.

We set up most nets back in the brush but in the final day when we needed to catch the last few stragglers we set up a long net lane along the path - it ended up being successful! Thrushes are ground feeders and took advantage of these walking paths - we caught five birds as they made their way onto the path.

Allison determining the age of a thrush by looking at its feathers and molt pattern.

One indicator is the shape of P10 (the 10th primary flight feather) - pointed (vs. rounded) indicates an older bird.

A geolocator and harness - the loops tucked around each leg with the geolocator extended above the feathers on the thrushs' backs. Each one weighed about a gram or less. 

Ready to go!