Metals in Feathers tell Migration Paths

Laura Font describes how she has found a way to find out where migratory birds have been by measuring strontium isotope ratios in feathers.
22 April 2007

Interview with 

Laura Font, Durham University


Chris - Every year, millions of birds migrate around the planet looking for a warm place to spend their winter and a cool place, with plenty of food, to spend the summer.  Keeping tabs on where they go and where they've been isn't easy.  We really need this information to help conservationists to protect threatened species and also to understand how diseases like avian flu might be spreading around.  Until now though, the process has been very difficult.  Attaching trackers to individual birds can be traumatic for the animals and it can also weigh them down, especially if they're small.  But now, Durham University researcher Laura Font has found a way around the problem using chemistry.  She measures the relative amounts of different isotopes, or forms, of the metal strontium in a bird's feathers. As the levels of these strontium isotopes very in a known way from one geographic location to another, and birds usually shed and then re-grow their feathers before they migrate, the strontium in the feathers can be used as a kind of chemical fingerprint telling researchers where the bird has come from.  Barn swallow (Hirundo rustica)</p><p>Laura -   We've been developing a technique to measure strontium isotopes in bird feathers because there's a biologist in the department of biology of Durham university who came to us with a problem.  Basically, they wanted to know if we could analyse the strontium isotopes in bird feathers to track migration paths.  This type of analysis has been done in bones of birds, but obviously you would have to capture the bird, kill it and extract a bone sample.Chris -   So what's the scientific basis for using a. Strontium and b. feathers?Laura -   The strontium ratios that we analyse in rock samples are very characteristic of the different morphologies and the age of the rock.  If a bird is in a particular environment with a particular type of rock, the ratio from this environment will also be in the tissues of the bird.  This is because the ratios of the rock will be passed to the soil and then to the plants, the insects that eat these plants and then the birds that eat these insects.  The strontium ratio goes through this chain.Chris -   And why do you use feathers?Laura -   Migratory birds change their feathers when they are in the winter location and the summer location, changing feathers each season.  So then each feather will reflect the ratios in the winter location or when they moult in the summer location.Chris -   So you can get a pretty accurate picture of where the bird has been, where it's come from and gone to.  These amounts of strontium must be absolutely tiny in the feathers, how do you actually measure it?Laura -   We use a special technique with micro-columns with a special label.  We dissolve the feather, we pass it through more columns and then we collect the strontium fraction.  We load the solution on filaments and we analyse it with a thermal ionisation mass spectrometer.Chris -   And that gives you a picture of what the relative ratios are?Laura -   That gives you a value, then you also have to analyse the soils and look at the geology of the areas where you think these birds spend their winters and their summers.Chris -   This is very useful for people who happen to like looking at where birds have come and gone but there must be some important medical and scientific principles which would benefit from this, I can think immediately that we're all worried about avian flu...Laura -   Avian Flu, yes, because if we manage to define very well the migration routes of migratory birds, then if we know that this is a species that can potentially carry bird flu, we can find the origin of carriers of the flu.


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