(NaturalNews) Some birds radically change their diets just before their winter migrations, gorging themselves on antioxidant-rich berries to prepare for their long journeys, researchers have found.
"[The] results support the hypothesis that some migratory birds may actively select deeply-pigmented fruits as a signal for meals that are rich in antioxidants," researcher Navindra Seeram of the University of Rhode Island said. "These disease-fighting antioxidants may help the birds combat stress and inflammation that they experience during long flights."
"It has been known for some time, this phenomenon of birds switching to fruits in the fall," said study co-author Scott McWilliams, a bird researcher.
The phenomenon is particularly striking because sparrows, thrushes, warblers and other birds with beaks highly specialized for eating insects suddenly begin using them to pick berries instead. A single bird can consume up to three times its weight in berries per day -- the equivalent of a human being consuming more than 300 pounds-worth of food.
"They look clumsy and ridiculous," said migratory bird researcher David Bonter of the Cornell Lab of Ornithology.
Researchers initially assumed that the birds were merely attempting to consume as many calories as possible before migrating, and that they turn to berries because insects are becoming scarcer.
"But that didn't explain it enough," McWilliams said.
Then researchers realized that many migratory birds were selectively eating darker-skinned fruits, which are known to contain higher levels of many antioxidants. This led McWilliams and other scientists to suggest that the birds might be deliberately seeking out foods high in antioxidants, which would help protect their bodies from the stresses of migration.
"Whenever we exercise, we undergo oxidative stress, and the same is true for birds," McWilliams said.
"When I started studying birds during their migratory stopover on Block Island, I was impressed that most of the migratory birds ate berry fruits even though they usually eat insects or seeds at other times of the year," he said. "I began studying the relationship between the nutritional qualities of fruits and how those nutrients might fuel migration."
Then McWilliams saw an article about Seeram, a new member of the chemistry faculty.
"I saw the story about Navindra, and in it he was talking about oxidative stress and inflammation and the effects berry fruits can have on reducing those impacts on people," McWilliams said. "Our colleague is very much a biochemist. His field is looking for compounds in nature that might have human benefits."
McWilliams contacted Seeram, and they agreed to team up and conduct an analysis of the birds' favorite foods.
In the first phase of the study, graduate student Jessica Bolser spent months observing birds feeding on Block Island, off the coast of Rhode Island. The researchers then collected ripe samples of 12 of the birds' favorite berries for analysis, including arrowwood, winterberry, bayberry, chokeberry and elderberry.
The birds' absolute favorite berry was arrowwood, which researchers found to be highest in antioxidants and pigments of all the berries tested. The fruit contained 650 percent more pigment than the average of the other 11 berries put together, and 150 percent more antioxidants.
"We know that a diet rich in antioxidants, like those found in fruits and vegetables, is good for human health," Seeram, PhD said. "As a chemist, I think it's fascinating to learn that migratory birds also seek out foods that are richest in antioxidants."
Seeram and McWilliams' colleagues immediately hailed the findings as new and significant.
"The whole twist of looking at the antioxidant qualities is novel," Bonter said.
"This study is one of the new generation of bird food studies that is ... not just looking at energy and protein but looking at micronutrients," said ecologist Douglas Levey of the University of Florida-Gainesville.
Seeram and McWilliams believe that the birds and the berries have probably co-evolved, with birds selectively eating the berries that provide the most antioxidants, then unintentionally repaying those plants by spreading their seeds far and wide through defecation.
"The smartest birds and the best berries seem to go hand-in-hand," Seeram said. "They need each other."
Further areas for study immediately suggested themselves. Bonter expressed interest in how the birds learn to seek out the darkest berries, noting that at the time of migration many birds have already left the nest and have no parents around to teach them.
"There must be some compounds in the fruit that serves as attractions," he said. "My guess is there are young birds testing a lot of fruit."
Bonter also wonders if a similar phenomenon might explain why many birds have different diets at their wintering grounds than they do during the rest of the year.
"Wintering birds do have a more omnivorous diet," he noted.
Because birds from all across the northern latitudes tend to pack into much smaller wintering grounds in the tropics, Bonter suggested, they probably undergo significantly more bodily stress. Analysis of their diets might find that these birds, too, are seeking out foods high in antioxidants.
Seeram and McWilliams noted that if more animals are found to selectively seek out antioxidant-rich foods, observing animal diets might eventually lead to the discovery of new useful chemicals.
"We've only measured a few of these antioxidants," Seeram said. "Our next step is to determine how birds can detect these compounds."
The two Rhode Island researchers have decided to continue their partnership.
"We're flying birds in wind tunnels to produce oxidative stress, and then we are going to see if antioxidants found in these berries alleviate that stress," McWilliams said.
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