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Linking Migratory Shorebird Habitats: The Power of Stable Isotopes
Effective
management of migratory birds requires that we know where they go for
the breeding and non-breeding seasons, and where they stop in between.
Traditionally, biologists have used leg bands for tracking the paths of
migrating birds, but for non-game species, banding has yielded relatively
little information about their seasonal movements. Consequently, biologists
cannot identify which habitats are limiting for many migratory species
because the links between seasonal habitats have not been clearly established.
In recent years, there has been a growing concern about the effects of
local, regional, and global changes on habitats for many migratory species,
including more than
30 shorebird species that breed in North America but spend the non-breeding
season in Central or South America. Wildlife managers from many countries
are working together to identify priorities and to focus their management
efforts to conserve migratory shorebird species. A promising new tool—stable
isotope analysis—may be helpful in their endeavor.
Recognizing the potential benefits of stable isotopes
for 
the
study of migratory birds, USGS biologist Adrian Farmer and geologists
Gary Landis and Robert Rye began a new study that will evaluate the use
of stable isotopes for linking the seasonal habitats of migratory shorebirds.
Stable isotopes of various chemical elements occur naturally in all ecological
systems, and are assimilated into all levels of food chains. When a bird
ingests water and food, its body tissues absorb the isotopes and take
on chemical “signatures” of the geographic area where it resides.
Scientists are investigating the possibility that isotopic analyses of
a bird’s tissues (e.g., feathers) may indicate the locations of its
breeding and non-breeding habitats and tell a more complete story about
its migration patterns.
Because of the hemispheric scope of shorebird migrations, it was obvious from the outset that international collaboration on the research would be essential. Moreover, accomplishing the study objectives would be dependent on the success of the South American aspects of the work. Hence, in January 2001, the three USGS scientists traveled to Argentina to meet with scientists there, collect preliminary data, and begin forming the partnerships necessary to conduct the study. While in Argentina they visited a range of wetland sites and discussed study design with Argentine scientists. As a result of their trip, the Universidad Nacional de Córdoba has established a graduate program to document the spatial variation in isotopic ratios across northern Argentina, and the Universidad Nacional de La Pampa is proposing a similar study further south in Argentina.
The study will also require the analyses of feathers
from the breeding grounds. Collaborators in Russia and Alaska collected
flight feathers from Pectoral Sandpipers (see
news brief: 10.29.2001) during the summer of 2001 from a wide range
of breeding locations as far west as the Taymyr Peninsula of Russia. Scientists
from Sweden and The Netherlands previously had collected feathers from
the Canadian Arctic that also will be analyzed. Collaborating scientists
expect isotopic analysis to be a powerful tool for identifying the linkages
between seasonal habitats, ultimately leading to more effective management
of migratory species.
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