Magic Mud and Bird Feeding Habits

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        ‘Magic mud’ uncovered on Vancouver tidal flats key to shorebird populations


        A February 2012 handout photo shows a western sandpiper slurping up the “magic carpet of biofilm” at Roberts Bank, just south of Vancouver on the Fraser River Delta. The biofilm, which scientists say is high in energy and nutrients, can make up to 70 per cent of shorebirds’ diet.

        The “magic” in the mud was first uncovered just south of Vancouver where up to half the world’s western sandpipers touch down to refuel as they migrate north.

        Now the gooey, paper-thin biofilm has also been found to be a key bird food on the other side of the Pacific, revealing what researchers say is a “missing link” in the avian world.

        Biofilm can make up to 70 per cent of the diet of small shorebirds, which slurp up the stuff like energy drinks, says Environment Canada researcher Robert Elner, who led the international team that reports its study findings this week.

        The scientists say the results could have big implications, especially for ports that may have been unknowingly destroying prime shorebird — and biofilm — habitat.

        Mud in the intertidal zone has long been considered “just mud,” says Elner. “It wasn’t regarded as particularly productive, or particularly beautiful. So it’s never been a valued resource.”

        Biofilm — or as Elner describes it “this magic carpet of biofilm” — alters that picture dramatically.

        Biofilm is a dense, mucous-like layer that forms on mud. It is created by bacteria and diatoms that settle out of seawater and secrete mucus that binds them to the mud so they won’t wash away with the tide.

        The film is composed of mucopolysaccharides, which is an easy-to-digest, high-energy food. Elner says it also appears to contain nutrients that keep the birds in good shape for migration and reproduction.

        The researchers from Japan, Britain and British Columbia’s Simon Fraser University explored six intertidal sites in Japan and Canada, and looked at 30 different shorebird species from red-necked stints to dunlins.

        They sifted through the birds’ droppings, examined their mouth parts, and set up high-speed video cameras to watch the birds racing across inter-tidal flats, rapidly feeding as they went.

        The analysis revealed the birds use their beaks — and hairy tongues — to suck up biofilm. The smaller the birds the more likely they are to consume large amounts of the high-energy goo.

        “Biofilm feeding is indeed widespread,” the researchers report this week in the journal Ecology Letters.

        They say the connection between shorebirds and biofilm is not only a “missing” but a “critical” link that could lead to better understanding of the birds, many of which are declining in number globally.

        Biofilm was never been thought of as a bird food until Japanese researcher Tomohiro Kuwae, of the Port and Airport Authority in Yokosuka, teamed up with Elner and his colleagues to examine why as many as a million migrating western sandpipers flock to the mudflats at Roberts Banks south of Vancouver each spring. They reported in 2008 that the sandpipers, which had thought to have been feeding on bugs and worms in the mud, were slurping up the “snot-like” biofilm.

        The new study says the feeding behaviour of the sandpipers at Roberts Bank is not unique.

        “It’s not just western sandpipers, it’s all small shorebirds worldwide are doing this,” says Elner, who is retired from Environment Canada but continues to do research for the department’s wildlife service.

        Biofilm is common to many aquatic ecosystems but the researchers say some tidal flats have currents and conditions more conducive to producing large amounts. Just how resilient the biofilm is to port and industrial activity is an open question.

        Wildlife ecologist and study co-author Ronald Ydenberg, at Simon Fraser University, notes that Rotterdam’s Europort in the Netherlands “obliterated” bird habitat. But he says others ports, such as the one at Seal Sands in Britain, are known for bird watching.

        “There is a way to do it well, and a way to do it poorly,” Ydenberg says of port development.

        Elner describes Roberts Bank as the “ecological crucible” of the Fraser River delta: “You’ve got huge economic pressures there, you’ve got huge ecological values.”

        And biofilm has added a sticky new component to environmental assessments of proposed developments.

        Roberts Bank is not only a key stop for migrating birds but home to Deltaport, western Canada’s busiest port and its five-kilometre long causeway that cuts across the mudflats.

        It is hard to know how the port affected the biofilm and sandpipers when it was first built decades ago, but Ydenberg says recent port expansion does not appear to have had big adverse environmental effects. “I believe it is possible to accommodate both,” Ydenberg says of birds and ports.

        But the scientists say there are plenty of unanswered questions about how the birds and biofilm would fare if the Deltaport expands, or if there were a spill at a fuel terminal being proposed by Vancouver airport.

        Darrell Desjardin, director of environmental programs at the Vancouver port authority, says future port expansions are being designed with biofilm in mind.

        “It is a valued ecosystem component, and something we take very seriously,” says Desjardin.

        Read more: ‘Magic mud’ uncovered on Vancouver tidal flats key to shorebird populations

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