Friday, June 6, 2003
Biodiversity Corner Ovenbird Seiurus aurocapillus
The Ovenbird is a wood warbler, but its appearance more closely resembles that of a small thrush. If you can get a good look at its head, you will see a yellow-orange stripe on its crown, hence its species name aurocapillus, from Latin meaning "gold hair." The species name Seiurus derives from the Greek seio meaning "to shake or move to and fro" and from oura meaning "tail" (Harrison, Ref.1).
Places in town you are likely to hear or see Ovenbirds are the Greenough Land, Great Brook Farm State Park, Towle Land and possibly even near your house. On Ken Harte's annual birding walk at Towle on May 18 several Ovenbirds were heard, and some lucky birders actually saw one. Several years ago, again on Ken's walk, the group passed directly below an Ovenbird perched on an overhanging branch. A novice birder happened to spot it and asked, "What's that bird?" As a consequence, we were all treated to a close look.
Ovenbirds, like most wood warblers, are primarily insectivorous, eating caterpillars, bugs, beetles, flies and ants; they will also eat spiders and other small invertebrates. Some warblers, such as Yellow-rumped and Pine warblers, eat some plant material, but animal material constitutes the bulk of the diet.
The female Ovenbird builds a dome-shaped nest, shaped like a Dutch oven; hence the bird's common name. The nest is located on or very close to the ground in areas with leaf litter and shrub under story. We once discovered a nest built in a rock crevice only a few inches above ground level. Harrison (Ref.1) states: "The female Ovenbird sits so tightly on her nest that she flushes only when almost stepped on. I know of some that have been so reluctant to leave that they have been accidentally trampled." The female lays 4-5 eggs, and incubates for a period of 12 days (Harrison, Ref. 2)."
According to Harrison, Brown-headed Cowbirds commonly parasitizes the Ovenbird nest. The female Cowbird lays its eggs in the nests of other smaller birds, and will even eject the eggs of the host species to make room for its own eggs. Most female host birds do not recognize the Cowbird egg as being different from their own and thus raise one or more Cowbirds. The young Cowbird is usually larger and more aggressive than the young of the host bird, and thereby wins in the competition for food from the parent.
Cowbirds parasitize the nests of many species of birds, although some host species recognize the foreign egg and either push it from the nest or abandon the nest and start a new clutch of eggs elsewhere. Ovenbirds and other ground-nesting birds such as Hermit Thrush, Rufous-sided Towhee, and Bobolink are also vulnerable to predation by house cats, raccoons, chipmunks, and other mammals. Researchers have found that large tracts of forest unbroken by roads and housing developments increase the nesting success of warblers and other woodland birds, since birds nesting near forest edges are more vulnerable to both avian and mammalian predators.
Ovenbirds head south in late summer, and by September most have left Carlisle. If you happen to be in south Florida during the winter, you might encounter a Carlisle Ovenbird on its winter ground. For those less fortunate, we must wait until the following May to hear its song of "Teacher, Teacher, Teacher" ringing through our forests.
The author is grateful to birder Steve Sauter of Ashfield, Massachusetts for permission to use his incredible Ovenbird photograph.
1. Harrison, Hal H. Wood Warblers World, Simon & Schuster, 1984, pp. 235-240.
2. Harrison, Hal H., Birds' Nests, Petersen Field Guide Series, Houghton Mifflin, 1975, p. 198.
Tom Brownrigg is a member of the Carlisle Conservation Commission. His interests include birding, nature observation and digital photography.
© 2003 The Carlisle Mosquito