Shore birds return to Delta
Spring is ushered in with long light evenings and the sound of bird song.
Skeins of snow geese have been passing overhead, and the big flocks of wintering ducks have almost all departed.
A group of mountain bluebirds fluttered near the dyke in Boundary Bay regional park. They posed on the split rail fence like a scene in a Robert Bateman painting, flashing azure blue against the grey brown grassland. They stayed only a few days on their migration to the parklands and subalpine of the Interior.
Western sandpipers make some of the longest journeys. Arriving from as far away as Peru and Suriname, they have thousands of kilometers to go before reaching their nest sites in the Arctic. These tiny birds feed in dense flocks on mud flats as the tide rises and falls.
Each species of shorebird is adapted for life on the beach. The large, long-billed curlew probes deep within the mud for crustaceans and worms (the female has the longer bill). Dowitchers repeatedly stab the mud with their dagger-like bills, using the rhythm and tenacity of a sewing machine needle, while black-bellied plovers stand watchfully alert nearby, ready to pipe the alarm.
Not all shorebirds are exclusively carnivores. Researchers in Delta were the first to discover that western sandpipers not only peck for invertebrates on the mud’s surface but also graze on sticky biofilm, sucking it up with their hairy tongues. This has led to the descriptive term “snot-feeding.”
According to local biologist Bob Elner, a large sandpiper flock can consume 20 tonnes a day of biofilm, a mucus-like coating of diatoms and bacteria that clings to the mud. It is particularly prevalent in areas like Roberts Bank around Brunswick Point, where hundreds of thousands of shorebirds gather during migration stopovers, in mid to late April.
By videotaping the birds as they fed, researchers were able to calculate that sandpipers probe the mud an average of 121 times per minute, poop every two minutes and swallow seven times their own weight in biofilm each day.
Delta’s local beaches and mud flats are inestimably important for the survival of these long distance migrants. While visiting our shores, sandpipers and other birds need peace and quiet to feed, so please keep your dog away from the flocks, and try to avoid interrupting their hectic feeding.
Those little birds still have a long way to fly before month’s end.
Anne Murray is the author of A Nature Guide to Boundary Bay and Tracing Our Past ~ A Heritage Guide to Boundary Bay, both available at local bookstores; see www.natureguidesbc.com.