Moving Bark or Fluttering Leaf
- Last Updated: October 26, 2016
Photos By Joe Halton
This bird is a fun one to spot on a fir tree trunk, though finding it can be challenging. The Brown Creeper (BRCR) is a little over 5 inches long with a decurved bill, white underside and brown speckled upper parts that look like bark. This perfect camouflage is why this bird is described as “a piece of bark come to life.” The Brown Creeper uses this camouflage pattern as a defense mechanism. When pursued, it will land on a tree trunk; flatten, and spread its wings while remaining motionless. Its pointed tail is medium length with strong spines and slightly curved feathers adapted for tree climbing.
The feeding behavior of BRCRs is interesting to watch. They hop up a tree similar to woodpeckers, but unlike woodpeckers they consistently ascend in a spiraling motion around the tree trunk to the top. Once to the top, they fly down to the next tree or even the same tree and repeat the pattern. They’re using their sharp decurved bill to probe for insects, larvae, spiders and eggs in-between and underneath the bark. Often in the same tree you may see a Brown Creeper ascending and a Red-breasted Nuthatch descending in their search for food. Scientist believe this opposite pattern is beneficial for both birds by limiting competition for the same food.
Though mostly solitary during non-breeding, BRCRs are sometimes observed in mixed-species flocks in winter. They group with Chickadees, Red-breasted Nuthatches, Golden-crowned Kinglets and Downey Woodpeckers. Ornithologists speculate there are two reasons why these species flock together. First, when a higher number of birds flee it is more confusing for the predator. Also, there are more birds to call warnings when a predator approaches. Secondly, and the strongest hypothesis is increased feeding efficiency. With mixed-species eating from a similar menu, they can feed in one area and move to the next avoiding trees that have already been searched for food. Each species has its own feeding technique and favorite food, thus limiting competition in the flock.
The most unique points of the breeding monogamous pair is nest type and location. Both the male and female agree upon the nest site which is usually behind a piece of fir tree bark. The female builds a hammock-style nest using twigs as a base. Then she combines bark, moss, fir needles, spider web and feathers into an elongated cup behind the tree bark. Sometimes the nest has an entrance facing down and an exit facing up. This is consistent with the ascending tree trunk behavior BRCRs exhibit. The male will bring nesting materials to the female and sing nearby while she constructs the nest. This process can take 6 to as long as 30 days to complete. Nests are often preyed upon by squirrels. The clutch size of 5 to 6 eggs is incubated by the female over about 2 weeks. The male will feed the female during this time. Both adults feed the nestlings for an additional 14 to 20 days. An interesting behavior of the fledglings is how they group together on a tree trunk in a circle with their heads facing inward and flatten their bodies against the trunk. At a young age they take advantage of their camouflage trait and the “safety in numbers” principle. A group of BRCRs is called a “spiral.”
Brown Creepers are year-round residents in Skagit County. Area parks with fir tree-lined trails are great places to observe mixed-species flocks in winter. Listen for the high-pitched buzzy “teesee” call of the BRCR, sometimes delivered twice. Their song is an accelerating series of descending notes which sounds like “trees trees pretty little trees.” Look closely for the “moving bark” climbing up the tree trunk and then “fluttering like a leaf” down to the base of another nearby tree. The camouflaged Brown Creeper is a fun one to find. Take a moment to appreciate this tiny bird.