American Dippers (AMDI) are a decidedly western “water bird.” CO ranks 5th among U.S. states for breeding populations, with 7% of the population. These amazing birds typically breed along fast-running streams and rivers; their loud wren-like chatter (often referred to as a buzzy “jik”) and extremely varied jumble of a bell-like song, individual and repeated notes and intermittent “jiks” ring out clearly over the sound of the river. North America’s only aquatic passerine, they “fly” under water, often bucking very strong currents and using their wings to propel themselves to capture aquatics insects. Their common name “dipper” comes from their habit of bobbing or “dipping” on the shore or a rock in the stream while they are looking for prey. An old name for them was “water ouzel,” a name for several species of European thrush (there, spelled “ousel”). However, although its body shape suggests some of the plumper species of that family of birds, the AMDI is most definitely not a thrush.
Below is a photo that perfectly captures how we typically see dippers in this area—a black, bobbing blob on skinny legs in the shadows on a rock in the river. Although the photo doesn’t do the bird justice, it accurately reflects our less-than-ideal glimpses. Luckily, dippers are easy to identify from afar by their “dipping” behavior; their rapid, shallow wingbeats as they fly low across the river; and their wren-like chatter. Although they don’t use nest boxes, they do sort of build their own cavities. So I’ve included them as part of our nest box monitoring effort.
We’ve been monitoring this site since we found it in 2007, atlasing for the 2nd Colorado Breeding Bird Atlas. (Others have known about the site for years; we were just a bit late to this particular party.) Dippers build very interesting dome-shaped nests of grasses and twigs very close to water; the entrance hole typically faces the water. Our priority block included a 2-lane bridge spanning the Arkansas River, so in early April we stopped by just to see if anything might be there. Much to our surprise, tucked into the corner of one of the bridge girders over the north bank of the river, was not only an AMDI nest but a lively, noisy group of nestlings clamoring to be fed. Our first species documented for the BBA—and it was a “confirmed” breeder. Score!!
Since we had missed the very beginnings of nesting behavior in 2007, we decided to try to catch it earlier the next year (2008). In early March, we found a AMDI nest under reconstruction in the same spot. (Some bird seemed to have built a nest on top of last year’s AMDI nest.) The photos here are of that nest; if you click on either of the photos, you’ll see a couple for red twigs at the entrance. We continued to check on the nest until about 3 weeks later, we found it smashed on the river bank. Since eggs were still in the nest, I can only assume it was the work of human vandals—any wild animal that might have taken it down would surely have eaten the eggs. (The spot was easily accessible to anyone by foot and indeed was just above a popular path of fishermen and teens intent on partying by the river.) Hoping against hope, I continued to check the bridge each week. About 2 weeks later, I found that the female was constructing a nest on a girder a bit further downstream and on the opposite side of the river—a spot much less easily accessible for humans. We continued to check weekly for a couple of weeks more; however, the winter’s record snowpack began to melt and the river rose rapidly. After 2 weeks, we could no longer get to the spot, so we left them in (hopefully) peace.
This year (2009), I began checking the bridge again starting in mid-February. No sign remained of the 2008 nest, but I heard 2 AMDIs singing. I saw no evidence of a nest until 4/1; a brief check showed a new half-dome of grasses started on a girder on the north side of the river (photo on the left). It’s on the “dangerous” side of the river again—and with such late start, it will again be in jeopardy of vandalism from warm-weather party-goers, I fear. On 4/10, we checked again—now a completed nest (photo on the right). Interestingly, with this year’s nest, we can again see 2 red twigs at the entrance—in the same place and in nearly the identical position. Sort of reminds me of a baby gate. I haven’t read about dippers routinely doing something like this. So perhaps this is the same female as last year, adding her characteristic touch?
We checked back on 5/1. The river was on the rise, but the site was still accessible on foot. As we approached, an adult flew from the area of the nest. Zell moved under the bridge to take a photo and realized that a bird was staring back at him from the recesses of nest. He took some quick photos up close. (And look—there’s the “baby gate,” still in place.) This bird is much lighter than any adult I’ve seen. For a time, we thought it must be a nestling that just suddenly appeared this mature. But given the dates of nest construction (an incomplete nest on 4/1), it just seemed much too quick. We solved that mystery when we stopped by the nest on 5/11. This bird was in this exact position again, but we could hear a chorus of tiny squawkings coming inside the nest. That mystery was solved–indeed, the female had been incubating the eggs, which had pretty recently hatched. We haven’t solved the mystery of such a light adult. Even outside the nest, she appears a much light taupe color than her mate. Just a fluke, perhaps.
Unfortunately, that last monitoring stop is probably the last chance we’ll have. n 5/11, the river was running at about 1010 cubic feet/second (cfs). The path was walkable, but just barley. The river is now rising fast due to extremely warm weather melting the snowpack and filling the upstream reservoirs to capacity. We stopped by on 5/16 (river at ~2300 cfs) and the path was under water. Much safer for the birds; disappointing for the humans. (Dipper nestlings all yelling from the entrance hole would have been a great photo. And it would have been fun to see if the “baby gate” remained through such wear and tear.) Alas–we leave them in peace.
© 2009 Tina Mitchell