Crucial pollinators dwindling, study says

Birds, bees, bats and other species that pollinate North American plant life are losing population, according to a study released yesterday by the National Research Council. This "demonstrably downward" trend could damage dozens of commercially important crops, scientists warned, since three-quarters of all flowering plants depend on pollinators for fertilization.

American honeybees, which pollinate more than 90 commercial crops in the United States, have declined by 30 percent in the last 20 years. This poses a challenge to agricultural interests such as California almond farmers, who need about 1.4 million colonies of honeybees to pollinate 550,000 acres of their trees. By 2012, the state's almond farmers are expected to need bees to pollinate 800,000 acres.

Gene E. Robinson, an entomologist at University of Illinois, Urbana-Champaign, and one of the 15 researchers who produced the report, said U.S. farmers had to import honeybees last year for the first time since 1922.

A number of factors have cut pollinators' numbers in recent decades, the researchers said. Introduced parasites such as the varroa mite have hurt the honeybee population, and pesticides have also taken a toll. Bats, which carry pollen to a variety of crops, have declined as vandalism and development have destroyed some of their key cave roosts.

John Karges, a Nature Conservancy conservation biologist who works with the endangered Mexican long-nosed bat in West Texas, said the bat's U.S. population fell from 10,000 in 1967 to 1,000 in 1983.

"This bat is rare and suspected of declining rangewide," said Karges, adding that it can now be spotted only at one protected cave site in Big Bend National Park.

Animals carry pollen — which they pick up inadvertently while feeding on a plant's nectar — and transfer it from one flowering plant to another, sometimes over distances. The process not only boosts plant production but also increases genetic diversity.

Animal pollinators fertilize more than 187,500 flowering plants worldwide; scientists believe these plants, called angiosperms, gained ecological dominance more than 70 million years ago in part because animals help them disperse their pollen so broadly. Other pollinators include hummingbirds and butterflies, as well as wild bees.

In many ways pollination works as a chain, said committee member Peter Kevan, a professor at the University of Guelph, Ontario, in which even the largest animals depend on small insects.

"Canadian black bears need blueberries, and the blueberries need bees" for pollination, Kevan said. "Without the bees you don't have blueberries, and without the blueberries you don't have black bears."

European researchers have also documented serious declines: The diversity of bee species has declined by 40 percent in the Britain and 60 percent in Holland since 1980.

So far, North American farmers have responded to the shortages by importing bees from Europe and elsewhere, but this strategy carries risks. These imported bees could bring new pests, parasites and diseases along with them, the study warned; the varroa mite came to the United States along with packaged bees.