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On the Trails: Loons, baby birds and springtails

Posted: August 9, 2013 - 12:03am
Two adult black oystercatchers hunt for invertebrates to feed their three young chicks.  Photo by Pam Bergeson
Photo by Pam Bergeson
Two adult black oystercatchers hunt for invertebrates to feed their three young chicks.

The East Arm of Glacier Bay is a wonder-world of gerrymandered geology. Rock walls are made of obviously different materials, all contorted into swirls and folds and cross-veins. The pebbles on the beaches could keep a rock hound happy for hours. So many stories in stone! Oh, if only we’d had a geologist with us.

We knew a little more in a biological way, and there were lots of biological observations of interest.

Red-throated loons called un-melodiously as they flew overhead, and family parties loudly yakked and squawked to each other. They nest on lakeshores and fly to nearby saltwater to forage. My best memory of them is our nest-searching effort, some years ago. My crew and I saw a pair carrying fish over a huge sand ridge, so we knew there had to be chicks somewhere on the other side. Ever-so-quietly, we belly-crawled up the side of the ridge and peeked over. But those loons knew we were coming! They stood there glaring up at us and did not reveal the location of the chicks. Hmph. Outsmarted by loons!

As always, finding bones leads us into mental exercises. A small bird’s pectoral girdle required some re-assembly (and memory-dredging). A very large sternum with an inflated keel may have come from a swan. Part of a fish jaw held three rows of tooth sockets in graduated sizes, prompting the question of who had owned this jaw and how, exactly, was it used?

Perhaps the greatest fun was provided by baby birds and their parents on the beaches. We watched a very aerobatic male yellow-rumped warbler capturing insects for a fluffy, bob-tailed fledging that scuttled over the beach cobbles, trying to keep up with its father. One bewildered young warbler blundered into my shoulder as I sat watching the show. Another found itself in our “kitchen” and perched on a bear barrel, briefly. We saw these woodland warbler families on many beaches, taking advantage of all the flying and crawling insects (We sure wished they would make a perceptible dent in the hordes of mosquitoes and blackflies and no-see-ums.)

Black oystercatchers were still incubating eggs on some beaches, but on others, chicks of various sizes scurried over the rocks or scrunched down, almost invisibly, beside boulders. Their parents were very busy, bringing shellfish and crabs to the insatiable youngsters. It seems that oystercatcher chicks need to be taught to peck at their food. We watched adults place a prey item in front of chicks and poke at it several times, before the chicks got the idea and pecked at it themselves. Every so often, the adults would fly off to join other oystercatcher pairs in screaming parties. A group of six or eight birds would fly back and forth just off-shore, yelling and hollering, for several minutes, and then each pair would go back to its own territory along the beach. Why do they do that?

A big puzzle came from observing billions of tiny springtails floating down the freshwater rivulets that often run across the beaches. They used their little forked spring-tails to jump off the water surface; they are so small that the surface tension of the water can serve as a launching platform. Hordes of these minute creatures floated and hopped down the little streams and congregated eventually at the edge of the cove. I imagine that they were still basically in fresh water, because that water is lighter than sea water and can form a layer on top of the salt water. But what was all this about? A mating swarm? Or, were they driven out of their usual haunts by something? And what are their usual haunts, anyhow — does this kind of springtail live in the interstices of the beach gravels, or somewhere upstream? Many unknowns!

One night, some of us were awakened by growling and snarling, very close to some of the tents. This generated some excitement and alarm, until more experienced ears identified the growler as a river otter, displeased at the human occupation of its beach. The next day, an otter swam by, inspecting the camp from the water. No doubt it was pleased when we left!

• Mary F. Willson is a retired professor of ecology.

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