While the isotopic analysis of feathers would not replace bands for individual
bird identification or for visual studies, it could be used to determine the
destinations of migratory birds ...
http://www.nature.com/nsu/020204/020204-11.html
Feathers track migrants' flight
Chemistry reveals birds' differing tastes in Caribbean islands.
08 February 2002
JOHN WHITFIELD
Chemicals in feathers have shown that one migratory bird species splits into two
groups that have separate summer and winter homes. Similar analysis could decode
other birds' movements and aid their conservation.
Black-throated blue warblers (Dendroica caerulescens) that breed in the
northeastern United States winter in the western Caribbean, Dustin Rubenstein of
Dartmouth College in Hanover, New Hampshire and his colleagues now report. Those
that spend the summer in the southern states head for the eastern Caribbean when
the weather turns cold.
The finding could explain why the species is in decline in the southern United
States. These birds migrate to the most heavily deforested islands in the
Caribbean, such as Hispaniola.
"We're not sure why they do this - we never knew to look for it before,"
Rubenstein says. One possibility, he argues, is that northern birds leave first
and fly over their southern counterparts to bag western locations in Jamaica and
Cuba. Differences
persist because "birds return to the same place year after year", he adds.
"It shows there are very different populations within the one species - nobody's
been able to come up with this level of detail before," says ecologist Keith
Hobson of the Canadian Wildlife Service in Saskatoon. Similar differences "are
probably typical of a vast number of species", he says.
Knowing where animals go will help researchers to work out why they are under
threat, and help to focus conservation efforts, Hobson adds. "Rather than just
saying 'this bird goes to the tropics', we can concentrate our efforts in a more
refined manner, geographically and politically."
Black box
Banding is the traditional way to track bird movements, but the chances of
recapturing a ringed bird are pretty slim. Satellite tags are expensive and too
heavy to attach to small birds.
But every animal is a chemical album of its travels. Variations in geology and
climate give each place a chemical signature. These signatures mark plants, and
pass up the food chain into insects, birds and beyond.
So feathers can be the black box of bird flight.
Black-throated blue warblers replace their feathers on their breeding grounds,
just before heading south. Plucking feathers at this point allowed Rubenstein's
team to map the proportions of different forms of carbon and hydrogen in birds'
migratory
plumage to their nest sites.
This meant that later, when the researchers caught warblers in the Caribbean,
they could tell where the birds had come from.
References
Rubenstein, D. R. et al. Linking breeding and wintering ranges of a migratory
songbird using stable isotopes. Science, 295, 1062 - 1065 (2002).
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