| Stable
isotopes are atoms of an element that have a different atomic weight than
the ordinary isotope of that element. Stable isotopes of common
elements such as hydrogen, oxygen, and carbon, are easily measured. The
ratio of stable isotopes of hydrogen in rainfall vary by latitude.
Plants, and the insects that feed on them, take up these isotopes.
As baby birds are
fed these insects, their new feathers also contain the unique isotopic
“signature” of the place where they were grown. In this way, scientists can analyze the ratio of stable isotopes in feathers taken from birds along their migratory path (or their wintering areas) and determine where the bird grew those feathers. For species that grow those feathers on their breeding grounds, the istotopic signature can be used to connect breeding areas with migratory stopover site. Where do our migrants come from? Some populations of migratory birds are in decline. Some declines are range-wide, others appear only in particular geographic locations. Good conservation and management decision can only be made by understanding where species nest, winter, and stop during migration. At RRBO, we have been studying the ecology of migrant songbirds for over 13 years. We now know which species use our area, which stay to rest and refuel, and which gain weight. A next step is to determine where these birds originate, which can help us answer questions such as: Are the birds that most often migrate through here from declining or stable populations? Do different populations migrate through our area at different times? Are the birds we recapture from certain regions? Which species do we need to target for site-level stopover habitat management? Our focal species include Swainson's Thrush, Gray-cheeked Thrush, Tennessee Warbler, Black-throated Blue Warbler, Blackpoll Warbler, Wilson's Warbler, White-crowned Sparrow, and American Tree Sparrow. These species are either of high conservation concern, have had other studies done with which we can compare, are poorly monitored on their far northern breeding areas, and/or species in which we have substantial stopover ecology data from our site. Feather sampling (two feathers per bird) began in the fall of 2004. Some analysis may be done in early 2005, but for the majority of species more sampling will need to be done in 2005. Major funding for
this project comes from DTE Energy
Links Linking
Migratory Shorebird Habitats: The Power of Stable Isotopes
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