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Ants in the pants drive birds away from choice fruit: supercolonies of invasive insects spoil avian picnics.

Dubbed "yellow crazy ants" by people, an invasive ant drives birds crazy too.

Nicknamed for their wild scurrying, the ants keep birds from eating and dispersing fruit, says ecologist Dennis O'Dowd of Monash University in Melbourne, Australia. On Christmas Island, an Australian territory in the Indian Ocean, hordes of yellow crazy ants (Anoplolepis gracilipes) storm onto birds landing on plants. Keeping ants off plant stems in invaded zones more than doubled the chances that a fruit would be bitten by a bird, O'Dowd and his colleagues report online September 15 in Biology Letters.

O'Dowd and others have been chronicling the ants' impact on the native creatures of Christmas Island since the 1980s, but this paper is the team's first to test ants' effect on fruit eating by birds.

"What never ceases to impress me is that something so small can affect vertebrates so directly," says Dennis Hansen of Stanford University, who has studied ants bedeviling geckos on the island nation of Mauritius.

On Christmas Island, yellow crazy ants have caused so many changes that O'Dowd and coauthor Peter Green of La Trobe University, also in Melbourne, have declared an "invasional meltdown" of the original ecosystem. Ants probably hitchhiked to the island sometime during the early 20th century and boomed during the 1990s. Supercolonies now cover swaths of the island in such density that ants in a feeding frenzy can clear a forest of its once-important red crabs. And ants climb onto and bother birds, too.

In ant-dense zones, O'Dowd sees birds stomp and ruffle their feathers as if maddened by crawling ants. To see if this nuisance affects the birds' feeding, coauthor Naomi Davis, now at the University of Melbourne, set out arrays of artificial fruits crafted from nontoxic modeling clay. In forests not yet invaded by ants, fake fruits showed more than twice as many peck marks as those in ant zones.


When Davis put an ant-trapping goo around the base of dowels holding her fake fruit in the ant zones, she found the goo's presence more than doubled the number of pecks from two native fruit-eating bird species. White-eyes and island thrushes were more willing to try the fruit when ants weren't raging over the plants.

Fruit eating could affect bird nutrition and population size and change the distribution of seeds, O'Dowd says. But, he adds, any ant-induced changes are probably complex and hard to predict.

Once highlighted mostly as a tropical phenomenon, ant invasions now menace temperate regions, says community ecologist Lori Lach of the University of Western Australia in Perth. Invaders have left seeds stranded without their native ant dispersers, lizards starving without palatable meals and flowers languishing for want of pollinating geckos, she says.

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Author:Milius, Susan
Publication:Science News
Geographic Code:8AUST
Date:Oct 10, 2009
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