Western Sandpiper Secret Revealed – It’s the Biofilm!

For many years, researchers have wondered why the huge mudflats of Roberts Bank, near Vancouver, are so special to migrating Western Sandpipers. Every year around 2 million Western Sandpipers stop to rest and refuel on these mudflats. This is a substantial proportion of the world’s population of this shorebird species. The area’s key importance for Western Sandpipers is one of the reasons why the entire Boundary Bay – Roberts Bank – Sturgeon Bank – Fraser River Estuary area around Vancouver is recognized as a globally significant Important Bird Area.

Now, recent research has revealed that the Western Sandpipers feeding at Roberts Bank rely heavily on what is called “biofilm”: a thin, dense layer of microbes, organic detritus and sediment which is all stuck to the mudflats in a mucous-like matrix. The Environment Canada biologist involved in the study points out that this matrix comprises a mucopolysaccharide, which is essentially, umm…snot. The snot binds the microorganisms to the mud and as a result they don’t wash away with tidal action. Biofilm’s not unique to Roberts Bank, but the area produces a lot of it because of the nature of the tidal action and the nutrients in the area that come from the Fraser River.
It turns out that the Western Sandpipers at Roberts Bank, numerous and ravenous little feeders that they are, consume up to 20 tonnes of biofilm a day. Biofilm accounts for 45 – 59% of the sandpipers’ total diet, and an average of 50% of their daily energy requirements during migration. This study is the first report of biofilm feeding for a higher vertebrate (previously it was thought that only invertebrates and a few specialized fish consumed biofilm). A slow mode video taken by the researchers highlights the “grazing” technique that the sandpipers use to harvest the biofilm. You can also watch the video below:

 

So, why is this important? Well, it helps us to understand just why migrating Western Sandpipers need to stop and refuel at Roberts Bank and not some other nearby mudflat: it’s the biofilm. And it highlights the particular importance and challenge of conserving this special place – we need to make sure that the mudflats and their biofilm are safeguarded. There is already a large container port, and all its associated traffic, close to where the sandpipers feed, and a projected port expansion could have serious impacts to the habitat (including the biofilm) in the area. We need to make sure the locations where the sandpipers eat, as well as what they are eating, are protected.

(Photo: T. Kuwae)