Spring Comes to Mud and Boundary Bays

March 20, 2012

Springtime is made for day trips to local parks. Here’s an interesting update on birdlife at Mud and Boundary Bays on the Surrey-Delta border featured in our best-selling guidebook 52 Day Trips from Vancouver

Access: To reach Mud Bay Park, take the Highway 10 exit from Highway 99 and follow King George Highway north to the Colebrook Road exit. Turn left on Colebrook, then left on 127A Street onto Railway Road. Alternatively, take the Highway 17 exit and follow Ladner Trunk Road east to Hornby Drive, then turn right onto 104th Street and follow signs to the Delta Heritage Air Park.

Despite appearances, things are not as they once were on Mud and Boundary bays, at least not for ornithologists who study the tens of thousands of shore birds that overwinter there on the Surrey-Delta border.

Long-held wisdom as to the feeding habits of waterfowl and dunlin, the two most prolific bird groups on the bays, was stood on its head with the recent release of a study coauthored by Robert Elner, a Delta-based Environment Canada researcher.

When reached by phone at his Okanagan residence, biologist and author Richard Cannings outlined the findings of the study, Biofilm Grazing in a Higher Vertebrate: The Western Sandpiper.

“Dunlin are overwintering sandpipers,” he said , “and we’ve always thought that when sandpipers poked their beaks in the mud, they were feeding on insects. Turns out they are actually slurping up biofilm, a type of paper-thin mucus—snotty stuff that clings to the surface. Sandpipers are vacuuming up 20 tons of snot a day.”

That “snot” is a nutritious mix of bacteria, diatoms (microscopic plants), and organic detritus.

Ponder that during an afternoon’s walk or cycle outing atop 16 kilometres of dikes and foreshore trails that ring the bays.

Time it right with high tides and sunsets and you’ll witness both a military-precision ballet of birds and a light show like no other on the west coast of North America.

Picture a canvas of endlessly shifting waves tumbling in a brown-and-white gestalt.

Hang that image midair above a tidal-marsh and eelgrass landscape that reflects a spectrum of electric colours: there’s no more magical place to be.

How do dunlin achieve such remarkable feats of aerial choreography?

Peter Davidson, B.C. program manager with Bird Studies Canada, has a hunch. When I asked him to explain, he theorized: “Watch them for a while and you’ll see they turn front to back like dominoes. I imagine the birds may follow what others are doing, taking cues from the leaders from one moment to the next. Dunlin have perfected synchronized flying to avoid peregrine falcons that feed on them. They can keep it up for as long as two to three hours at a time. With Mount Baker in view behind, it’s a stunning sight.”

As winter-weary denizens yearn for warmer weather, one of the best places to dry out is the 5.5-kilometre stretch of trail that links Surrey’s Mud Bay Park with the Delta Heritage Air Park.

Although the drone of traffic from nearby Highway 99 intrudes in places, most of the route is comfortably distanced beside intertidal wetlands.

Budget 75 minutes on foot.

Along the way, the cast of the daily performance grows well beyond diminutive shore birds and songbirds to include blue herons, red-tailed hawks, and bald eagles.

“There are big numbers of eagles right now,” Davidson noted. “The annual cycle of abundance is finished for them. All the salmon runs are done on inland rivers, so they come here and to Roberts Bank to feed on ducks, gulls, and offshore birds. In early October, 30,000 to 40,000 ducks gather around Mud Bay and hang around until April. With the arrival of the eagles, waterfowl are fed up with being picked on and are more dispersed.”

One rare visitor attracting plenty of attention this winter is the snowy owl; according to the Ladner Christmas bird count, there were 38 in the region.

Reached by phone, Nature Vancouver director Jude Grass recalled: “An eruptive year like this hasn’t happened since 1973-74. That first time when I visited, I saw 30. The next year, I returned expecting to see them again and wondered where they went.”

To be overflown by a snowy owl can be both astonishing and exhilarating.

Until the last moment, all that appears is a sculpted oval face, more like a ceremonial mask than a winged creature.

“As long as the cold weather persists, they should be around until mid-March. It would be interesting to know where these ones come from: Siberia?” Gross mused.

“There are at least 22 at the south foot of 72nd Street in Boundary Bay Regional Park. Just hop up on the dike and walk a bit in either direction. They shelter between the dike and the tide line.”

Grass pointed out that although there is an upside to the public curiosity surrounding snowy owls, it has also provoked unwanted attention from overeager photographers intruding in the posted no-go intertidal zone.

“I heard one photographer boast he had over 1,800 images of snowy owls. Who needs that many?”

To be fair, with so much magic in the air, it’s hard not to fall under the spell nature casts over the bays.

Just stay off the snot.