In the last column we embarked on an historical wild goose chase. I am tracing the development of our understanding of bird migration through the ages. The Barnacle goose (this European vagrant was seen recently in Aroostook County) was the centerpiece of the last column. Its name came from the medieval misconception that Barnacle geese and barnacles are different stages of the same animal.

Humans did not really get a handle on bird migration until the 18th century, finally putting Greek myths about hibernation and transformations to rest. In 1749, Johannes Leche began recording the spring arrival dates of Finnish birds. As we will see, these types of records can be valuable in understanding migration.

The first published statement of bird migration appeared in Thomas Berwick’s A History of British Birds in 1798. Berwick disputed the prevalent notion that British swallows hibernated, writing “they leave us when this country can no longer furnish them with a supply of their proper and natural food …”

From around 1900, local bird clubs have been collecting arrival and departure dates for migratory birds. By reading these local reports, an observer could determine that ruby-throated hummingbirds arrive in the Gulf Coast in early March, around April 10 in Virginia but not until early May in New England. The wave of migration of North American birds thus becomes evident through the shared observations.

We have come a long way since Leche’s lonely records in Finland. Central depositories like ebird.org hold millions of records, so the patterns of northward spread in the spring and southward withdrawal in autumn are clearly seen. If you haven’t tried the tools under the explore data link on ebird, give it a try.

Plotting the arrival and departures of migratory birds gives us insight into bird populations but not individuals. Do ruby-throated hummingbirds that cross the Gulf of Mexico and land in Louisiana continue their migration to the Midwest while those that land in Florida migrate up the Atlantic seaboard? We must track individuals to answer such questions.

Bird banding is just the tool we need to follow individuals. James Audubon almost certainly banded the first birds in North America. In 1840, he tied a silver thread around the legs of several eastern phoebe nestlings on his farm near Philadelphia. Two of the phoebes came back the following year. Of course he had no idea where the phoebes went to pass the winter, but he established the power of banding individual birds

The North American Bird Banding Program (NABBP), begun in 1920, facilitates the banding of birds in the United States and Canada. After extensive training, a person is provided with a bander’s permit and is given aluminum bands, each with a nine-digit number. Banders capture birds in nets or traps, identify the species, sex and age of each bird, take various body measurements, affix an aluminum band to one of the legs of the bird and release the bird.

If another bander captures the bird or if a banded bird is found dead, the finder contacts biologists at the NABBP who provide the recovery data to the original bander and notify the finder of the original date and site of the banding. Over the 94 years of the program, more than 64 million birds have been banded and 3.5 million have been recovered. We have learned much about subpopulations of migratory species that maintain different migration routes, as well as information on fidelity to wintering and breeding sites over the years.

Even greater detail of migration routes can be gleaned from satellite transmitters mounted on birds’ backs or from small data loggers called geolocators that track a bird’s geographic position continuously. A geolocator has to be recovered to download the data, unlike a satellite transmitter. How cool is it to monitor an osprey’s migration from your computer desktop?

Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader questions and comments at

whwilson@colby.edu

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