Wading for Bugs: Exploring Streams with the Experts

9. Dicos for Ducks

52 9 Dicos for Ducks Judith Li Harlequin ducks are brightly colored birds that get their clownish name from their decorative white eye rings, white cheek spots, and burnt orange, white, and deep gray wing plumage. Our research team called them “harlys.” In the winter of 1996, Kris Wright and I were into our second year of studying how harlys used the rock-cased caddisflies Dicosmoecus gilvipes for food at Quartzville Creek. This alder-lined stream flows over boulder cascades and bedrock flats as it rushes through a canyon headed towards the Santiam River in western Oregon; during spring, it is a playground and nesting area for harlys. Adult birds spend the winter at Dicos for Ducks 53 the ocean surf off the Oregon coastline then migrate inland to freshwater streams. Harly pairs build nests in the canyon’s rocky nooks; the males then exit and females are left to raise their young. The chicks’ gray and white markings camouflage them well, but in the spring of 1995, when we looked very carefully, we’d see chicks following their mothers, bobbing up and down in stream riffles, foraging for stream insects. By late January of 1996, Quartzville Creek was running fast and full to the edge of the banks. Young Dicosmoecus, barely one half of an inch long, were crawling in the “surf zone” where the stream gently lapped against sands, gravels, and plant roots. The young caddis lumbered about with diminutive cases constructed of thin leaf bits and conifer needles. Each tiny larva’s head stuck out as the front pair of legs crawled along, dragging the small woody case that protected its soft abdomen. The larvae made do with the pieces of flotsam available in early spring, and Dicosmocus is one of the few caddisflies out and about in early spring. That year we expected to follow another annual cycle of caddis growth and harly activities, but things would prove to be different. On January 25th, the weather report was of a “rain on snow” event—rain and a heavy snowpack melting quickly during a sudden warm spell. That meant potential flooding downstream. In Corvallis, the Willamette River came about two inches short of cresting its banks and flowing into downtown. Kris heard that the stream runoff was very high in the mid-Cascades, so he set off on the hour’s drive to Quartzville as soon as the highways were clear. I waited for him in the warm comfort of our lab. “Trees were down everywhere along the Quartzville road,” Kris reported when he returned. “Before I could reach our study sites, I ran into a roadblock where the hillside slumped and had poured mud, boulders, wood across the road and into the stream—what a mess!” Then Kris’s mountain biking skills had kicked in. Climbing up and over the landslide, he had surveyed the damage very quickly. The view was quite a surprise: “The log the size of a semi-truck in the middle of our reach, the sandbar with the willows around 54 Sleuthing for Caddis it: they’re gone! That huge boulder perched at the top of the little waterfall is nowhere to be found. From the signs of stream debris hung up in the tree limbs, I think the stream must have gone way up onto the banks where we set up our sampling last year. Who knows what happened to the critters in the stream?” To answer that question we combed the stream looking for the caddisflies during March and into April. In normal years Dicosmoecus grow and continuously build cases using strands made by their silk glands, eventually including bits of sand. By late April they generally have molted three times, when their cases take on the shape of tiny cornucopia, skinny on the ventral, or tail, end, and about one quarter of an inch wide at the dorsal opening. This makes room for their heads and crawling legs. When their bigger, heavier cases are made entirely of sand and gravels, “dicos” have ballast to move out onto the bedrock in the middle of the stream. In Oregon, one-inch-long, rock-cased caddisflies grazing on algae in the middle of the stream are usually Dicosmoecus. But in spring of 1996, the year of the big flood, we saw only a handful of dicos. Two months after the flood, right on schedule, fourteen harlequin ducks came back from...