The inside of a duck's intestine may not win any prizes for passenger satisfaction, but for freshwater fauna, it is the long-haul carrier of choice. That is the finding of research published in this month's issue of Global Ecology and Biogeography. The new study shows that small invertebrates can be transported over hundreds of kilometers by migrating birds.
Many tiny freshwater critters such as water fleas and bryozoans are wingless, so biologists always wondered how they manage to spread between lakes and ponds. The hypothesis of transport in the guts of migratory birds has repeatedly been pooh-poohed by ecologists. By the start of the bird migration season, skeptics point out, water flea eggs and dormant stages called "statoblasts" in bryozoans would have sunk to the muddy bottom, out of reach of foraging birds. To solve this conundrum, ecologists Jordi Figuerola and Andy Green of the Doñana Biological Station in Sevilla, Spain, and Luis Santamaría of the Netherlands Institute of Ecology in Nieuwersluis decided to take a more direct look at the birds' cargo.
During both autumn and spring, the researchers stalked flocks of migrating ducks and other birds in the Doñana wetlands in southern Spain, an important stopover for birds migrating between Europe and Africa. After a group of birds had left, the team collected what the birds had left behind. Sifting through more than 400 droppings with fine-meshed sieves, they discovered that two-thirds of the samples contained hundreds of water flea eggs, bryozoan statoblasts, and even fragile water bug eggs. The microscopic resting stages must be regularly swallowed by birds mucking about in the lake bottom, Figuerola says.
The results may have important implications for global biogeography, Figuerola adds. It often takes more than 24 hours for food to pass through a duck's guts, enough time for the birds to travel up to 1300 km. So ducks and other birds may help aquatic animals colonize new habitats over very long distances. In fact, an as-yet-unpublished study by Figuerola shows that in North America, the genetic relationships among water flea populations clearly follow bird migration paths. With the possible exception of boats and their bilge water, "birds are probably the most important way of dispersal," he says.
"It's a neat study," says zoologist David Bilton, who studies aquatic invertebrates at the University of Plymouth, United Kingdom. He points out that, perhaps not surprisingly, "this is the first time anyone has bothered to quantify the passage of [invertebrate] eggs through waterbird guts."
Related sites
The Doñana Biological
Station
FreshwaterLife, a
freshwater information resource
)
)
)
)
)
)
)
)
)
)
)
