Western Purple Martin Foundation

BC Purple Martin Migration Study

A new state-of-the-art migration tracking study is now underway for Western Purple Martins.

Until recently it has been impossible to directly track Purple Martins to their South American wintering grounds as GPS satellite tags are much too heavy for use on these small birds. New miniature light-level geolocator data loggers recently developed by the British Antarctic Survey (www.birdtracker.co.uk) were originally designed for tracking movements of large seabirds and are now small enough to use on songbirds like Purple Martins. These tiny electronic devices record time and light intensity every 10 minutes, which allows us to determine the bird’s position daily (+/- ~300 km) from the day length and sunrise and sunset times.

A recent study on eastern Purple Martins by Dr. Bridget Stutchbury et al (2009) showed that these new miniature geolocators can provide detailed information critical to understanding spring and fall migration routes used by Purple Martins, important stopover/feeding areas used during migration and where they overwinter in South America.

Project Starts - Summer 2009

geolocator application

Details about spring and fall migration routes and wintering areas for Western Purple Martins are almost entirely unknown. With financial support of $4950 from Shell Environmental Fund and participation of Georgia Basin Ecological Assessment and Restoration Society, the Vancouver Island University Biology Department and dedicated VIU Biology students, we were able to start a BC-based migration tracking study for these birds in 2009.

geolocator application

We put miniature geolocators on 20 adult Purple Martins at several colony sites on Central Vancouver Island in July and August 2009. The geolocators were attached with a tiny “backpack” harness around the legs, a design which neither harms the bird nor interferes with its movements. The martins wore the geolocator data loggers until they returned from their South American wintering grounds in spring 2010. Geolocators have a battery life expectancy of >1.5 years, retain the data indefinitely, and must be recovered to retrieve the data.

Year Two - Summer 2010

We were able to identify the adult birds that returned in 2010 by the presence of their geolocator and/or a bright orange coloured leg band. Four birds (two without geolocators) were observed. The two birds carrying geolocators were located at the colony site in French Creek. We had to wait until the birds started nesting and roosting in the boxes before we could attempt to box trap them in order to retrieve their geolocator. Unfortunately, one of the two birds left the colony due to nest failure before we could remove its geolocator. Hopefully that bird will return again next year and we will be able to recover the geolocator at that time. The second geolocator was successfully retrieved and its data was downloaded for computer processing.

geolocator on bird

Once the information from the data logger was downloaded, we were able to analyze the raw light data (maximum light intensity reading recorded within each 10-minute interval) to obtain latitude/longitude coordinates for each day from the time the geolocator was applied until it was removed 11 months later. Preliminary analysis indicates that the martin carrying this particular geolocator flew through the western states, spent some time at a fall roost in the American Southwest, then flew through Central America and spent the winter in southern Brazil, returning by the reverse route in the spring of 2011. This migration from BC to SE Brazil and return was ~22,000 km long!

geolocator birds release

In addition to analyzing recovered data, we applied ten more geolocators in July 2010, thanks to the financial support of TD Friends of the Environment Fund. We also attached seven geolocator facsimiles as controls. Any geolocators retrieved next year will provide additional information about migration paths and wintering grounds for Western Purple Martins. Whether different martins take the same paths, use the same roost sites or go to the same wintering grounds remains to be seen.

In August and early September the BC martins headed south for the winter. We now have to wait patiently for the martins to return in April 2011.

Year Three - Summer 2011

Three of the ten birds fitted with geolocators in 2010 returned in 2011. The first 2 were spotted at Ladysmith Maritime Society Community Marina and were successfully retrieved. The third geolocator was also successfully retrieved from a Purple Martin nesting at the Buckley Bay colony.

A fourth geolocator was spotted at the Deep Bay colony and was a surprising find. This bird had its geolocator put on in 2009 and was the same bird that had eluded capture in 2010. This year the bird cooperated and its geolocator was successfully retrieved. The older versions of geolocators had a larger battery pack and this one remained operational and recorded information for both its 2009 and 2010 migration routes!

putting on geolocators

Data analysed from several of the geolocators show that these Purple Martins followed a similar route to and from Brazil as the one previously tracked. The information gathered from the other geolocators is currently being processed and will add greatly to our knowledge of Purple Martin spring and fall migration routes.

With financial support from the Canadian Wildlife Federation, geolocators were put on 20 more adult martins at Ladysmith Maritime Society Community Marina this past summer. We are now waiting patiently for the Purple Martins to return in 2012 to see how many more geolocators can be successfully retrieved.

Reference:
Stutchbury, B. J. M., S.A. Tarof, T. Done, E. Gow, P. M. Kramer, J. Tautin, J. W. Fox and V. Afanasyev. 2009. Tracking long-distance songbird migration by using geolocators. Science 323: p. 896. www.sciencemag.org


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Website funded in part by the Ladysmith Maritime Society
Original website design by Danielle Morrison
Last modified 27 Feb 2012