Track me if you can
30 July 2009
Researchers have developed a technique that lets them track Cory's shearwaters migrating from the north to the south Atlantic and back again just by analysing the birds' feathers.
The technique is set to help scientists work out where and when these birds are vulnerable to threats such as fishing, pollution or global warming and may help to develop better conservation strategies.
Previous research has shown that oil spills and commercial fishing are directly responsible for drops in populations of seabirds, sharks, turtles, dolphins and seals across the globe. To stand any chance of stopping these declines, conservationists need to know where and what time of year these animals are most likely to be exposed to damaging human activity.
'Our results show that this technique can be used to figure out where the birds' feathers were grown and so where they breed and overwinter.'
Professor Jacob González-Solís, University of Barcelona
Scientists have traditionally used data loggers to track migratory species. But this approach is limited. Only a few individuals tend to be tracked for short periods of time, loggers are expensive and often lost and, because of their size, they cannot be fitted to small birds..
Professor Jacob González-Solís and his team from the University of Barcelona as well as colleagues from the British Antarctic Survey developed a new technique to counter this problem. Their idea was to exploit the fact that isotopes - different forms of the same chemical element - are distributed unevenly around the world.
This means that birds will have slightly different isotopes in their feathers depending on where they grew them.
'Feathers grow at a precise time of the year - some when the birds are breeding and others when the birds are overwintering. They're inert once they're formed and if we know the birds' moulting patterns we can chose the right feather to get some idea of what was happening in the environment when each feather was grown,' says González-Solís.
González-Solís and his team describe in the journal PLoS ONE how they tagged 25 Cory's shearwaters throughout the year with so-called light level geolocators - devices that reveal where the birds have been.
A year later
After a year, the researchers retrieved the locators to see where the birds had travelled. They also took samples from primary feathers grown during the breeding season as well as secondary feathers grown where the birds overwintered. They analysed these samples to see which isotopes they contained to see if the locations the locators revealed coincided with the locations the isotopes revealed.
'Our results show that this technique can be used to figure out where the birds' feathers were grown and so where they breed and overwinter,' says González-Solís.
Their results showed that the birds foraged within a few hundreds of kilometres of their colonies in the Canaries, the Azores and the Balearics. They also found that the birds wintered in specific but distinct areas of the Atlantic rich in fish, like the Canary, Benguela and Agulhas currents off the coast of Africa and areas off the coast of south Brazil and Uruguay.
When they compared breeding and wintering locations to the proportions of different isotopes in the feathers, they found that the proportions of isotopes in the birds' primary feathers depended on the breeding site. But the proportions of isotopes in the secondary feathers depended on the wintering area the birds had been to.
'Our technique should be applicable to many other migratory marine creatures and could help in different conservation efforts,' adds González-Solís.
Ramos R, González-Solís J, Croxall JP, Oro D, Ruiz X (2009) Understanding Oceanic Migrations with Intrinsic Biogeochemical Markers. PLoS ONE 4(7): e6236. doi:10.1371/journal.pone.0006236
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