Songbird migration tracked for the first time
13 February 2009
For the first time scientists have tracked songbirds like wood thrushes and purple martins during their epic migrations from North to South America and back again.
Purple martins were tracked in the study.
The team report in the American journal Science that the birds can fly more than 500 kilometres (300 miles) a day. Previous research estimated roughly 150 km (93 miles) a day.
One purple martin took 43 days to reach Brazil during autumn migration, but in spring returned to its breeding colony in just 13 days.
The Canadian team, led by Professor Bridget Stutchbury from York University in Toronto mounted geolocators, miniaturised by scientists at the British Antarctic Survey, on 14 wood thrushes and 20 purple martins in 2007.
The geolocators, which are around the size of a five pence piece but much lighter, are mounted on birds' backs 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.
Stutchbury says that researchers at the British Antarctic Survey 'hadn't really been thinking of [attaching them to] songbirds, but when I saw the technology, I knew we could do this.'
The wood thrush.
Songbirds, the most common type of bird in our skies, are too small for conventional satellite tracking. 'Never before has anyone been able to track songbirds for their entire migratory trip,' adds Stutchbury.
Electronic engineer James Fox from the British Antarctic Survey says, 'We've been developing and building these devices since 2000. Every year they've been getting smaller and smaller.' 'They measure light level. From this we can infer time of sunrise and sunset. From this we can estimate location'
'We are producing the smallest geolocators in the world and have been used on anything from fur seals to purple martins.'
A miniature light level logger (geolocator) for tracking animal movements for long periods.
In the summer of 2008, the team retrieved the geolocators from five wood thrushes and two purple martins and reconstructed individual migration routes and wintering locations.
'We were flabbergasted by the birds' spring return times. To have a bird leave Brazil on April 12 and be home by the end of the month was just astounding. We always assumed they left sometime in March,' said Stutchbury.
The study also uncovered evidence 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.
'This region is clearly important for the overall conservation of wood thrushes, a species that has declined by 30 percent since 1966,' said Stutchbury. 'Songbird populations have been declining around the world for 30 or 40 years, so there is a lot of concern about them.'
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