Rocky Brook Ruminations
Salmon Eating Songbirds
I’ve lived next to dippers (Cinclus mexicanus) for almost twenty years. They are year-round residents along Rocky Brook here on the Olympic Peninsula of Washington State. I see and hear them nearly every day. They stand on rocks, perusing the stream, bobbing or “dipping” up and down on their legs, and then plunging head first into the water. Initially I assumed that they mostly ate caddisfly larvae and other small invertebrates (bugs) which are common amongst stream bed rocks and gravels.
Then, one January day I observed a dipper “working” in an area I knew to be a salmon redd, a place where eggs had been laid a month earlier. Clearly the bird was feeding on developing salmon eggs. This was not really that surprising; the eggs were just sitting there within the gravel, certainly some were easy to get to, and this was a world that the dipper knew well.
I thus learned that dippers eat salmon eggs. Then last fall I learned something else.
Rocky Brook has a small hydroelectric plant just upstream from me. It’s turbines are fed by a large water tank abut 800 feet above it. The tank is fed by a system of intakes buried in the stream bed, carrying water in 4 ft diameter pipes, first to the water tank, and then to the turbines. Since the watershed is relatively small, the plant only operates during the winter, completely shutting down during the dry, usually rainless months from June through October. To start the plant again each year, the operator flushes the storage tank, releasing water into the creek just above where I live.
This water has been sitting for months. It has sediment, algal growth and rusted iron from the tank and penstock pipes. When released, it is an opaque, reddish, mud slurry. Each release event clouds the creek for two to four hours.
It was during this flushing that I noticed the dipper, right below my yurt. It was standing on a rock by the edge of the creek, diving into the thick muddy water, and coming up with a two inch long salmonid fry (most likely a coho or rainbow trout). Now this was a surprise for me.
After all, dippers do not seem to be adapted to catching fish. They do not gain speed and dive like a kingfisher. They do not have webbed feet and a serrated bill like mergansers. They are technically songbirds, related more to robins and wrens than to fish-eating waterfowl.
But here, right before my eyes, was a dipper with a little fry in its beak. It couldn’t swallow it, the fry was half as big as its head. So it proceeded to shake it violently, drop it on the rocks, pick it up, shake it some more, and even beat it against a rock. I watched as the fish escaped, got into the water, and then was recaptured ( the fish likely stunned and disoriented). Eventually the little fish stopped fighting and remained motionless on a rock. The dipper picked it up and flew away, so I was unable to actually see how it swallowed the little fish, but I have to assume that it found a way.
The key here is that the muddy creek water forced the fry to the margins where a dipper could capture one. I don’t think they would fare as well with fry in clear water. But it did alert me to the fact that dippers would eat little fish if given the opportunity, and had figured out how to do this under these unusual circumstances.
A month later, the creek bottom was a thick carpet of leaves. I thought this would impair the dippers normal feeding, making it harder to find bugs. Not so. Dippers did their usual dance on a rock, dove completely under the surface and worked under the leaves. Eventually it would surface with a worm-like larvae, shake its head violently to stun the insect, and swallow. This was common feeding behavior.
Dippers tend to be residents wherever they live, even in Alaska. When I was living in Homer, Alaska about ten years ago, I went out cross country skiing along the Anchor River. It was January, there was at least five feet of dry snow on the ground, air temperature in the twenties. Ski conditions were perfect. We followed the river as it was covered with snow and presumably ice below. We came to one spot where there was an opening, and we could hear the river flowing below. To my astonishment, a dipper appeared out of nowhere and dived into the hole. About a minute later it exited and headed off to I don’t know where. I thus learned that this little grey songbird somehow survived even Alaskan winters, staying active, finding food. Most likely it spent most of its time downstream, where the river emptied into the sea and there were more ice-free patches, but it also ventured upstream, looking for openings in the ice.
American dippers are only found along rivers in the western mountains from Alaska down into Mexico. An unlikely water bird at first glance they look like a short tailed songbird. Yet, they have some unique adaptations to their dependence on food right out of the rushing river or creek where they live.
First, their bones are solid, not hollow as in most songbirds. This makes it easier for them to dive. While they do not have webbed feet, they do have powerful wings which are used like flippers. They have a very dense plumage, and a very large preening gland for water-proofing their feathers. Underwater, they are covered by a thin, silvery film of air bubbles trapped in their feathers, a kind of insulation from the cold water. They have very long, sharp claws which aid in grasping rocks. They are able to change the curvature of the lenses in their eyes, allowing them to see clearly underwater. They have nasal flaps which prevent water from entering their nostrils. Dippers have especially high levels of hemoglobin in their blood, allowing them to store oxygen and remain underwater for 30 seconds or more. They are able to feed underwater even in freezing conditions (quite likely keeping a diving hole clear in rivers that freeze over in the northern part of their range).
During the spring, their territorial and mating songs are as rich and beautiful as any songbird.
My favorite time to watch dippers is during the summer when the young are learning to feed for themselves. Parent birds appear to feed their young for quite some time; the young will be almost as large as the parents, yet remain rooted to a rock, chirping loudly for food, refusing to dive into the water. The parent will dive and bring a juicy morsel and give it to the waiting offspring rooted to the rock. This results in a moment of quiet, before the loud begging begins again.
The chattering of the family can be quite loud and raucous (their voices are high pitched so as to be heard above the usual roar of the stream), and the young seem to need a considerable amount of time and coaxing to actually dive into the water and learn how to find food. That first plunge must be an amazing experience, opening up a whole new world.
Whenever you find yourselves along a mountain stream, stop a moment and watch the rocks in the water. Chances are quite high that eventually a dipper will appear, bob up and down on the rock, and surprise you by diving right into the rushing water.
And, listen for its song.