A new genetic marking technique may replace old-style bird-banding surveys as the most effective method for assessing declines of songbirds, which are important environmental indicator species.
Using new DNA sampling techniques, conservation biologists from San Francisco State University's Center for Tropical Research (CTR) have laid the foundation for a new method of assessing population declines in neotropical migratory songbirds, something researchers have been unable to do using traditional bird-banding methods.
Citing confidence in the results of a three-year pilot study by CTR, the U.S. Environmental Protection Agency is funding the second phase of research, which begins this month.
According to CTR Director Dr. Thomas Smith, researchers seeking clues about widespread songbird declines using banding studies (in which birds are caught, tagged, and then released for later recapture) are limited by their inability to link breeding and wintering populations of at-risk species. For example, of the 142,000 Wilson's warblers banded on North American breeding grounds over a 20-year period, only three were recaptured in their wintering grounds. Genetic marking techniques, on the other hand, can reveal important details such as where in Mexico a small breeding population of Wilson's warblers from the Bay Area spends its winter each year.
" If you can link wintering and breeding populations, you can tie-in land-use patterns contributing to their decline. This information is critical to establishing any species recovery plan," said Dr. Smith, an SFSU professor and evolutionary ecologist. "This is science and policy on the same track. "
These melodious migratory birds, which flock north each spring from Latin America to find mates and fledge offspring, are important environmental indicator species. Sensitive to habitat degradation, their declines raise the same early warning sign about environmental health that their doomed cousin, the canary, did for working conditions in coal mines.
As such, the EPA has awarded CTR a $330,000 grant to produce three more years worth of research, with the goal of using this genetic marking technique as a new method of relating wintering and breeding populations, in order to answer definitively whether these birds are in decline.
"The EPA feels there needs to be a new approach and method to studying migratory bird populations," said Clyde Bishop, manager of biology programs for the EPA. "If using genetic analysis proves feasible as a method, it can help us define more targeted, effective conservation programs."
Research team members Mari Kimura, an SFSU biology graduate student, and Borja Mila, director of the Point Reyes Bird Observatory's Latin America Program, have spent the last three years collecting and analyzing blood and feather samples from three species-Wilson's warbler, Swainson's thrush and MacGillivray's warbler. Using mist nets and field equipment, the researchers gathered samples from throughout the birds' migratory ranges, including breeding grounds in the Bay Area and 13 wintering sites extend ing from Mexico to Costa Rica. Team members are submitting their data for publication.
Beginning this month, under a post-doctoral fellowship provided by the EPA grant, Dr. Sonya Clegg will arrive from the U. of Queensland (Australia) to assist Dr. Smith in the direction of the project. The CTR team also collaborates with Dr. David Desante of the Institute for Bird Populations, which, through its Monitoring Avian Productivity and Survivorship Program, has provided the research team with more than a thousand feather samples collected from breeding grounds throughout the U.S. and Canada.
After extracting DNA from the blood or feather, team members sequence the DNA, then identify a molecular marker that shows a high frequency of haplotypes, or "tags," that are unique to specific geographic areas and subpopulations. For example, the genetic tag of a subpopulation of Wilson's warblers from Northern California was shared by a group wintering in Costa Rica. Since songbirds show a high level of geographic fidelity, linking haplotypes between breeding and wintering sites reveals a clearer picture of year-round habitat-use.
"Our preliminary analyses of mitochondrial DNA sequences demonstrates that the population structure of a neotropical migrant can be understood," said Dr. Smith, who is on the board of the Point Reyes Bird Observatory. With a more complete set of genetic samples, we hope to identify population units at a fine scale, which will provide the foundation for developing accurate assessments of demographic trends and the effect of land-use patterns on these important migratory species."
The Center for Tropical Research conducts basic and applied biological research in order to better understand essential biotic processes that produce and maintain tropical biodiversity worldwide. The Center is an auxiliary research unit of SFSU's College of Science and Engineering.
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