Early environment may be key to determining bird migratio...(h mangrove. The birds from the lower ren...)
h mangrove. The birds from the lower rent district leave later for breeding grounds, must migrate farther north, and when they return to Jamaica, the mangrove is occupied and they are, once again, scrabbling in the scrub.
The Cycle
The cycle begins for the young redstart when it leaves its northern birthplace and migrates south for its first winter. Studds team measured a hydrogen isotope called deuterium, found in the fledglings tail feathers, an indicator of where the bird was hatched and, in subsequent summers, where it breeds. Once the isotope in the feathers, it doesnt change, Studds says.
The isotope measurement showed that the birds that had the good fortune to spend their first winter in the mangrove stayed in the good life, while the birds that had wintered in the dry area usually had a harder life year round.
The birds in the lush mangrove have access to more insects, which helps them maintain their weight, says Studds. This helps them to leave sooner on spring migration and arrive sooner in the more southern breeding areas, where spring is just beginning,
The birds in the dry area, however, need about another seven days to bulk up, a long time, says Studds. The later start means that by the time they head north, the southern breeding habitat is already taken and the birds have to keep flying, some as far north as Canada, to find the right spring conditions for breeding.
Where a redstart spends its first winter also seems to be determined, in part, by its ability hold its territory. About seventy percent of the birds in the mangrove are males, Studds says. In the harsh habitat, they were mostly females and young males.
Climate Change and the Redstart
While these redstarts appear to be thriving today, the research team says their findings point to the need to consider conservation measures in the winter habitat.
The models predict increasing drought in the Caribbean, says Studds. Rain i
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| Contact: Ellen Ternes eternes@umd.edu 301-405-4627 University of Maryland Source:Eurekalert |
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