THE DAILY BUCKET IS A REGULAR FEATURE OF THE BACKYARD SCIENCE GROUP. IT IS A PLACE TO NOTE ANY ObsErvations YOU HAVE MADE OF THE WORLD AROUND YOU. RAIN, SUN, WIND...INSECTS, BIRDS, FLOWERS...METEORITES, ROCKS...SEASONAL CHANGES...ALL ARE WORTHY ADDITIONS TO THE BUCKET. PLEASE LET US KNOW WHAT IS GOING ON AROUND YOU IN A COMMENT. INCLUDE, AS CLOSE AS IS COMFORTABLE FOR YOU, WHERE YOU ARE LOCATED. EACH NOTE IS A RECORD THAT WE CAN REFER TO IN THE FUTURE AS WE TRY TO UNDERSTAND THE PATTERNS THAT ARE QUIETLY UNWINDING AROUND US
|
At this time of year a detour across the Skagit River delta nearly always rewards us with wonderful bird life like Snow Geese and Trumpeter Swans, although wild creatures are unpredictable and you never know what you might see. On our visit last week we witnessed something new and incredibly spectacular — a murmuration of shorebirds filling the sky.
Crossing the flat delta, mostly soggy fields now, I could see a wispy black cloud out over the mudflat. We found a place to park, climbed up onto the berm and were nearly knocked over by thousands of Dunlins swirling across the whole sky, swooping inshore then up and around in a single mass. This flock of about 5000 birds flew in concert, creating eery constantly-morphing three-dimensional shapes.
We stayed until the sun began to set. I took some photos, in between exclaiming incoherently... whoa...unreal...incredible...and just watching. Such a spectacle is beyond words, as anyone who has seen this in life will agree. But I will describe a bit of what’s happening and why.
(As a sidebar, note that I am using photos I’ve imported from Photobucket. You can see why in the pair below: the DK image library presents the same image considerably smaller. The Image Library is more convenient to use but since the switch to DK5 the quality of images presented on the website has declined significantly. I’m really hoping DK will at least bring back Lightbox, which hugely improved the size and resolution of photos. Communication is about more than words — images convey information words simply can not. To any admins who might be seeing this, when you get other things sorted out, please please look into fixing the Image Library problem!)
See the Trumpeter Swans behind the shorebirds?
Sometimes this flock coalesced, quivering momentarily like a giant beetle...
...then all the birds shifted direction, nearly disappearing as their light undersides now faced us instead of their dark upper surface.
The flock collapsed, flattening onto the water’s surface, snaking away at high speed.
How do they do this, and why?
Dunlins come to the Pacific coastline in winter to fatten up before migrating to northern Alaska and Canada to breed. About 30,000 winter in Washington state, and the Skagit delta is a favorite spot. The river has been flushing fertile sediment onto the delta for millennia which has mostly been converted into agricultural fields. Offshore, Skagit Bay is shallow and protected, an extensive rich intertidal mudflat full of amphipods, worms and other invertebrates. Shorebirds also feed in the flooded fields nearby.
A few hundred Dunlin flew in close to shore where we were, alighting briefly on driftwood. You can see their pointed beaks for probing mid-depth into the mud or soil. For a few minutes they fluttered on this log, packed with birds, with more trying to find a spot to perch.
Then they all rose at once, swept past us, merging with the larger flock. Golden sparkles, flashing in the light of the setting sun.
People have marveled at murmurations forever. While many birds flock only a few species can do this: starlings, some blackbirds, and shorebirds. Scientific investigation has revealed that there is no leader to a flock, and each bird is only watching its nearest 6 or 7 neighbors. Each individual's task is to avoid collision, stay close to others of its kind and move in the direction the flock is going. The speed of their reaction suggests telepathy, but it’s really a wave of movement, birds anticipating a shift from beyond their position. Like a wave moves through water faster than the water itself, the shifting movements in a murmuration are a wave of information, incredibly accurate across a great distance and faster than we can perceive in real time.
Why do they create these spectacular and dynamic forms, with thousands of individuals behaving as a single unit? One reason is to consolidate the gigantic flock before settling in to roost for the night. Considering how close to sunset it was I thought that might be what was going on. But if you look beyond this group in the photo below you can see many thousands more Dunlins across the bay, murmurating separately.
Eventually we had to go...it was getting dark and we were far from our destination. As I turned away, a Northern Harrier flew overhead toward the mudflat. Harriers prey on shorebirds and the Skagit delta is a rich feeding ground for raptors as well as for the shorebirds. But raptors have to catch one bird at a time or risk a dangerous collision. This murmuration of Dunlins protects each of the thousands of birds by confusing and distracting an airborne predator. Woe to a Dunlin who strays outside the flock. Even this juvenile Harrier could snatch it out of the sky. It’s likely this Dunlin flock rose up from the mudflat where they’d been feeding when this or another raptor threatened them. They are far more vulnerable on the ground.
These still photos show you the Dunlins I saw. For a sense of what the flock looked like in motion, you can watch this video, which was filmed in right here in the Skagit delta. Enjoy the spectacle!
~~~
What’s happening in your natural world? All nature observations welcome in the comments.
"SPOTLIGHT ON GREEN NEWS & VIEWS" IS POSTED EVERY SATURDAY AT 5:00 PM PACIFIC TIME AND WEDNESDAY AT 3:30 ON THE DAILY KOS FRONT PAGE. IT'S A GREAT WAY TO CATCH UP ON DIARIES YOU MIGHT HAVE MISSED. BE SURE TO RECOMMEND AND COMMENT IN THE DIARY. |