Public release date: 4-Apr-2006
Northern birds are fatter!
"The further birds migrate north for the summer, the faster they put on
weight", says Dr Williams (Simon Fraser University, Canada) who has
been tracking migrating birds for several years. "This research may
have implications for the designation of protected areas which will
ensure birds can complete their spring and autumn migrations." Dr
Williams will present his research on Tuesday 4th April at the Society
for Experimental Biology's Annual Main Meeting in Canterbury [session
"Our data can be used to assess habitat quality and the importance of
specific sites for migratory birds, and this can contribute to
decisions about whether migratory sites are protected and which sites
are prioritised for protection", explains Williams.
Two techniques were used to study Western Sandpipers on their spring
journey along the Pacific 'Flyway' from Mexico to Alaska: 80 birds were
fitted with radio-telemetry tracking devices and a further 400 had
blood samples taken to give measurements of fattening rate. Williams
found that birds fatten more rapidly as they move further north – as
they get closer to the breeding grounds - and that the longer the birds
spend hanging around at San Francisco Bay (one of the more southerly
refuelling sites), the lower their fattening rates.
Such differences in fattening rates cannot simply be explained by
differences in the availability of food. "Our current thinking is that
the difference in fattening could be caused by differences in behaviour
(birds simply feed more intensively in the north) or changes in
physiology that the birds experience as they move further north", says
Williams. "We know there are major differences in gut structure and
digestive enzymes between non-migrating and migrating birds, so there
might also be similar alterations in migrating bird's physiology
further north, which allow more efficient digestion."
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