Did you know there is a species of Asian babbler – the only babbler species in the New World – found solely on the western edge of North America? Neither did WC.
Wrentits are a member of the family of birds called Sylviidae. The family includes the Old World sylviid warblers, parrotbills and their allied species. Why is there a species of Sylviids on the west coast of North America? Good question. Wrentits are pretty weak fliers; they don’t migrate. In fact, they are sometimes described as the most sedentary bird species in North America.
Wrentits are found only between the Columbia River and southern Baja California, mostly along the Pacific Coast but in lesser numbers east to the Cascade Mountains and Sierra Nevadas. In that narrow range, they stake a territory out, usually in fairly dense brush, and defend it against other Wrentits year-round. Generally, from deep in a thicket.
This species is remarkable in other ways, too. They mate for life and, unlike other so-called monogamous species, they don’t seem to cheat. Both male and female birds incubate the eggs and feed the kids. The male and female both defend the territory. Outside of breeding season, the male, female and last batch of kids roost cooperatively, forming contiguous “feather-balls,” and mutually preen.
The male and female keep in constant vocal contact year-round. While full songs from male and female are probably used primarily for territorial proclamation at all times of year, partial songs seem to be used to maintain contact between mates and within family groups post-fledging.
Most of what we know about Wrentits comes from two epic studies of the species. One was by Mary M. Erickson and her supervising professor, Joseph Grinnell, in an intensive 4-year study in a chaparral canyon in Berkeley, California. Erickson did a year-round study, documenting the life history of 21 territorial pairs and individuals. The second was a long-term study by Geupel and DeSante at the Palomarin Field Station in coastal Marin County, California, involving 67 pairs which were followed annually in coastal scrub, with more than 4,685 individuals uniquely color-banded and more than 1,087 nests monitored. For an obscure, skulky species with a limited range, they are reasonably well understood.
Ironically, Wrentits may benefit, at least temporarily, from the clearcutting occurring in the Coast Range. The short term effect is to create a lot of scrub growth on the pillaged hillsides, the kind of habitat Wrentits love. Of course, a dozen or more other species, including the endangered Northern Spotted Owl and Marbled Murrelet, are serious losers, but the Wrentits do seem to prosper. Ir’s not all good news; the fragmentation of Wrentits’ preferred coastal scrub habitat by human development, in particular, is a concern. Juvenile dispersal is seriously disrupted by that habitat fragmentation, especially because the species is not a strong flier.
A fascinating species that WC had never before photographed.