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CO2 Increases Impact Songbird Feeding

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  • mtneuman@juno.com
    Media Contact: Todd McLeish 401-874-7892 http://www.news.uri.edu/releases/html/04-0126-05.html Global warming may cause songbirds to avoid certain foods URI
    Message 1 of 1 , Feb 4, 2004
      Media Contact: Todd McLeish 401-874-7892


      Global warming may cause songbirds
      to avoid certain foods
      URI student researcher: Chickadees avoid caterpillars
      that eat leaves exposed to high levels of CO2

      KINGSTON, R.I. -- January 26, 2004 -- In yet another example of the
      far-reaching impact of global warming, a University of Rhode Island
      student found evidence that suggests some songbirds may avoid eating
      insects that consume leaves exposed to high levels of carbon dioxide.

      URI senior Martina M�ller of Kingston, working in cooperation with
      Associate Professor Scott McWilliams, Ph.D. candidate David Podlesak and
      colleagues at the University of Wisconsin, studied the food preferences
      exhibited by black-capped chickadees.

      "When plants are grown in conditions of higher carbon dioxide, they
      produce increased levels of several secondary compounds -- tannins and
      phenolics -- that they use to defend against herbivory," said the
      23-year-old wildlife conservation and biology major. "Those secondary
      compounds are absorbed by gypsy moth caterpillars that feed on the
      plant�s leaves, which other researchers have found reduces the
      caterpillar�s growth rates. We wanted to see if the chickadees can detect
      the secondary compounds in the caterpillars and if they have preferences
      for caterpillars that fed on different types of leaves."

      Using chickadees captured in Kingston and acclimated for three days,
      M�ller and McWilliams fed the birds a choice of caterpillars that were
      high in tannins or phenolics and other caterpillars low in those

      "It was clear that the birds could tell the difference between the
      different caterpillars and they had strong preferences," M�ller said.
      "They�re intelligent birds with a keen capacity to learn."

      While the birds showed a distinct preference for caterpillars low in
      tannins and phenolics, they also showed a preference for foods they had
      eaten previously. "Previous experience does affect their preferences,"
      M�ller said.

      So what does all this mean? According to McWilliams, it could mean a
      great deal in a world that is growing warmer due to increasing levels of
      carbon dioxide in the atmosphere. "These results provide a much more
      complete and realistic picture of how elevated atmospheric CO2 might
      affect ecological systems."

      Since increased carbon dioxide leads to elevated levels of secondary
      compounds in plant leaves and decreased growth rates of caterpillars that
      eat those leaves, McWilliams said "birds that primarily eat herbivorous
      insects like caterpillars may find themselves without enough to eat as
      atmospheric CO2 levels increase. In short, chemicals in the caterpillar�s
      food influences the likelihood of predation by birds."

      In addition, he said that if birds avoid feeding on gypsy moth
      caterpillars, for instance, an uncontrolled population of the
      caterpillars could result in more severe forest defoliation.

      McWilliams also sees a connection between M�ller�s results and the
      current mad cow disease concerns in the U.S. "We know that mad cow
      disease can be transmitted to humans if we eat beef from cows that have
      eaten feed with the disease. So to safeguard our beef, we feed cows food
      that does not contain the disease. Birds seem to pay attention to this
      same rule: know what the food you are eating has eaten, because it can
      affect your health. In the case of birds, however, they seem to be one
      step ahead of us in that they are able to detect the secondary compounds
      in the food and change their feeding behavior accordingly."

      Funding for this research was provided by the National Science
      Foundation, the URI Agricultural Experiment Station, and the URI Coastal
      Fellows program, a unique program designed to involve undergraduate
      students in addressing current environmental problems. The caterpillars
      and aspen leaves used in the project were provided by Professor Richard
      Lindroth and Ph.D. candidate Jack Donaldson at the University of

      For Further Information: Scott McWilliams 401-874-7531

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