Bridget Stuchbury on Tracking Long-Distance Songbird Migration

Fast Moving Front Commentary, September 2010

Bridget Stuchbury
Photo credit: Douglas Morton

Article: Tracking Long-Distance Songbird Migration by Using Geolocators

Authors: Stutchbury, BJM;Tarof, SA;Done, T;Gow, E;Kramer, PM;Tautin, J;Fox, JW;Afanasyev, V
Journal: SCIENCE, 323 (5916): 896-896 FEB 13 2009
Addresses: York Univ, Dept Biol, 4700 Keele St, N York, ON M3J 1P3, Canada.
York Univ, Dept Biol, N York, ON M3J 1P3, Canada.
Tom Ridge Environm Ctr, Purple Martin Conservat Assoc, Erie, PA 16505 USA.
British Antarctic Survey, NERC, Cambridge CB3 0ET, England.

Bridget Stuchbury talks with and answers a few questions about this month's Fast Moving Fronts paper in the field of Plant & Animal Science.

SW: Why do you think your paper is highly cited?

Billions of individual songbirds leave their breeding grounds in North America and Europe and fly thousands of kilometers to spend the winter in tropical countries, creating one of the most spectacular animal migrations in the world. We were the first in the world to track individual songbirds to their tropical wintering sites and back; previous tracking devices (like GPS or satellite tags) were too heavy for small birds.

Until our study, researchers relied almost entirely on short distances or time frames to understand songbird migration. The ability to track small birds over their entire flight, which can amount to a trip of over 15,000 km per year for the bird, is a revolution in animal ecology and allows researchers to discover amazing new facts about migration speed and strategy.

Until our study, it was impossible to track individual songbirds to their wintering areas, which is essential for predicting the population consequences of tropical habitat loss in tropical regions. Wood thrushes, a species we tracked, have declined by over 30% in the past four decades but it is unknown how tropical deforestation in a particular region will impact specific breeding populations.

Geolocators provide a tool for novel and ground-breaking studies in conservation and migration ecology, and are now being used widely to study species that are declining (e.g. Eastern loggerhead shrike, Bicknell's thrush, painted bunting, bobolink, Eastern kingbird). Researchers have also begun similar studies on a wide range of other small birds including owls, swifts, and shorebirds.

SW: Does it describe a new discovery, methodology, or synthesis of knowledge?

Figure 1:

(2)	Light detecting MK10S geolocator (1.1g) and U.S. penny, taken by Juan Bahamon.
Light detecting MK10S geolocator (1.1g) and U.S. penny, taken by Juan Bahamon.

View larger image in tab below.

My study used a newly miniaturized tracking device called a "geolocator," designed by my collaborators at the British Antarctic Survey, to track the migration of wood thrushes and purple martins. The geolocators, which are smaller than a penny, detect light, thereby allowing researchers to estimate a bird's latitude and longitude by recording sunrise and sunset times.

The devices are mounted on a bird's back by looping thin straps around their legs. The weight of the geolocator rests at the base of the bird's spine, so as not to interfere with its balance.

SW: Would you summarize the significance of your paper in layman's terms?

We tracked the migration of wood thrushes and purple martins by outfitting them with tiny geolocator backpacks designed by the British Antarctic Survey. Songbirds, the most common type of bird in our skies, are too small for conventional satellite tracking.

We found that scientists have underestimated the birds' flight performance dramatically. Data from the geolocators indicated that songbirds can fly in excess of 500 km (311 miles) per daywhereas previous studies using other methods estimated their flight performance at roughly 150 km (93 miles) per day.

We found that songbirds' overall migration rate was two to six times more rapid in spring than in fall.For example, one purple martin took 43 days to reach Brazil during fall migration, but in spring returned to its breeding colony in only 13 days.

Prolonged stopovers were surprisingly common during fall migration in both species. The purple martins, which are members of the swallow family, had a stopover of three to four weeks in the Yucatan before continuing to Brazil. Four wood thrushes spent one to two weeks in the southeastern United States in late October, before crossing the Gulf of Mexico, and two other individuals stopped on the Yucatan Peninsula for two to four weeks before continuing migration.

We also found that wood thrushes from a single breeding population did not scatter over their tropical wintering grounds. All five wood thrushes wintered in a narrow band in eastern Honduras or Nicaragua—and since that first year we've had over a dozen more geolocator returns with similar results. Conserving forest in this region is clearly important for the overall conservation of wood thrushes, a species that has declined by 30% since 1966.

SW: How did you become involved in this research, and how would you describe the particular challenges, setbacks, and successes that you've encountered along the way?

We discovered these new tiny geolocators through attending an international conference (NAOC 2006 in Veracruz, Mexico), a great example of how bringing scientists together sparks the imagination and possibilities.

In the first year of using geolocators, and subsequent years, we have seen normal return rates in wood thrush for birds carrying geolocators. For purple martins return rates were lower than normal in the first year (10%) so we reduced the weight and size of the geolocator and now are finding that 50-60% of geolocator martins return safely, similar to non-geolocator birds.

You cannot get any data from geolocators unless the bird returns AND you are able capture it to retrieve the geolocator for download to a computer. It is frustrating to know that a bird has successfully completed a remarkable migration, but then not be able to catch the bird get the data. The good news is that we have retrieved over 90% of the geolocators that we know have come back.

But sometimes the device fails prematurely (about 10%) so after all these efforts we see only part of the journey, or none at all (ouch!)...but this technology is so new and amazing that to discover where "our" birds go, and how, makes the frustrations worth the expense and effort.

Figure 2:

(3)	Wood Thrush equipped with geolocator feeding young at its nest, taken by Elizabeth Gow.
Wood Thrush equipped with geolocator feeding young at its nest, taken by Elizabeth Gow.

View larger image in tab below.

Despite the challenges, it is still amazing to catch a bird carrying a geolocator and have the chance to know how this little bird flew thousands of kilometers!

SW: Where do you see your research leading in the future?

The Purple Martin Conservation Association and my lab have expanded our collaboration to include researchers who have deployed geolocators on martins in British Columbia, Texas, and Virginia. We will be able to find out how breeding populations map onto wintering sites in South America and how migration distance and breeding location affects migration routes and timing. We are also testing if birds infected with blood parasites have delayed migration or alter their routes.

We published a geolocator study on fall migration in wood thrush (Proc. R. Soc. B published online 21 July 2010 doi: 10.1098/rspb.2010.1220) showing that late breeding does not delay arrival on the wintering grounds.  We have also deployed dozens of geolocators on wood thrushes on their wintering grounds to find out how late winter arrival affects survival and which breeding populations depend on a particular tropical rainforest. In 2009 and 2010, my students have deployed geolocators in Costa Rica and Belize and will return this fall to retrieve the data.

SW: Do you foresee any social or political implications for your research?

Many migratory songbirds are undergoing long-term population declines, in large part due to winter habitat and stopover site loss. Identifying the stopover and wintering sites of specific breeding populations is critical for understanding how breeding versus over-wintering events contribute to population declines.

Knowing where breeding populations spend the winter, and vice versa, is critical for focusing conservation efforts in regions where they are needed most, and for establishing new and more effective international partnerships in migratory songbird conservation.

The ecological effects of the BP oil spill in the Gulf of Mexico will extend surprisingly far into the northern US, Canadian boreal forests, and the arctic. Migratory birds throughout North America will be affected because the Gulf coast is a prime destination for migrants and vital crossroad for dozens of bird species.

By September and October songbirds that bred in places like Alberta, Minnesota, and Tennessee will be piling up by the millions in Gulf coast forests and wetlands to fuel up for their marathon flight across the Gulf of Mexico on their way to tropical climes. My tracking studies of wood thrush and purple martins show that many individuals that breed far away in northern Pennsylvania stop along the Gulf coast from Louisiana to Florida on their migration, and therefore will encounter the oil spill disaster.

The scale of the oil spill is enormous, and for BP their responsibility extends to dozens of nations who share these migratory birds as a natural resource.End

Bridget J. M. Stutchbury
Department of Biology
York University
Toronto, ON, Canada


Select the tab(s) above to view larger photos and descriptions.

Figure 1:

Light detecting MK10S geolocator (1.1g) and U.S. penny, taken by Juan Bahamon.

Figure 1:

Light detecting MK10S geolocator (1.1g) and U.S. penny, Image taken by Juan Bahamon.

Figure 2:

Wood Thrush equipped with geolocator feeding young at its nest, taken by Elizabeth Gow.

Figure 2:

Wood Thrush equipped with geolocator feeding young at its nest. Image taken by Elizabeth Gow.



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