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Friday, July 25, 2014

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For the birds

Winged predators seek certain trees when foraging for caterpillars

— Irvine, Calif., January 26, 2012 —

Location matters for birds on the hunt for caterpillars, according to researchers at UC Irvine and Wesleyan University. Findings suggest that chickadees and others zero in on the type of tree as much as the characteristics of their wriggly prey.

Unfortunately for caterpillars, munching on tree leaves that are healthy and tasty can dramatically boost their own risk of becoming food. Study results, published online this week in The American Naturalist, show that dining on the trees that are most nutritious for caterpillars – such as the black cherry – can increase by 90 percent their chances of being devoured by a discerning bird.

“The jump in risk is surprising,” said co-author Kailen Mooney, assistant professor of ecology & evolutionary biology at UCI. “It shows that for caterpillars, moving from one tree to the next can mean the difference between getting eaten and surviving.”

The findings indicate a “neat potential pest control system,” because the healthiest tree species harbor the greatest number of caterpillars, thereby offering the easiest pickings for winged predators, said lead author Michael Singer of Wesleyan. “Our study addresses basic theoretical questions in ecology, but we also want forest managers and conservation biologists to take away practical knowledge.”

Mooney, who specializes in the ecology of predatory birds, said tree identification is probably learned by birds, not genetic. He added that Southern California bird species probably do the same with coastal sage scrub, determining which types of bushes afford a better chance of tasty insect treats.

With help from a small army of students, the scientists conducted a two-year experiment in Connecticut forests involving hundreds of tree branches either covered with bird-proof netting or left bare.

Mooney noted that the results illustrate a stark choice between gaining strength through a good diet but being more vulnerable to predators and remaining weaker and hungrier but more safe.

“If a caterpillar could feed on nutritious, high-quality tree species and be left alone, this would be the best of all worlds,” he said. “Instead, it’s faced with a trade-off. Overall, it appears that it’s better to feed on poor-quality tree species and have fewer caterpillars around you than to be on a nutritious plant with many others.”

About the University of California, Irvine: Founded in 1965, UCI is a top-ranked university dedicated to research, scholarship and community service. Led by Chancellor Michael Drake since 2005, UCI is among the most dynamic campuses in the University of California system, with nearly 28,000 undergraduate and graduate students, 1,100 faculty and 9,000 staff. Orange County’s second-largest employer, UCI contributes an annual economic impact of $4 billion. For more UCI news, visit www.today.uci.edu.

News Radio: UCI maintains on campus an ISDN line for conducting interviews with its faculty and experts. Use of this line is available for a fee to radio news programs/stations that wish to interview UCI faculty and experts. Use of the ISDN line is subject to availability and approval by the university.

black-capped chickadee
Christian Skorik / Wesleyan University
A black-capped chickadee prepares to dine on a caterpillar

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