A Song for April 28

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Click the sonogram to hear and see the sound.

"California's a Garden of Eden," wrote Woody Guthrie, and an island as well, according to a book by Elna Bakker, walled off as it is by mountains, desert, and sea. This is a perfect situation for high endemism, which is biogeographical parlance for having lots of species that are found nowhere else. Colonization of islands is a rare event, and so once a founding population makes it to such a place, gene flow from its source population can be quite low. A case in point is the California Thrasher, featured above. It's a bird of chaparral, also a California specialty.

Endemics may be distinct, but they do have relatives, and this thrasher has a celebrated family, the Mimic Thrushes (Mimidae). It includes mockingbirds, catbirds, and numerous other thrashers, including nine others members of the genus Toxostoma, most of which occur in the U.S. They are all vocal acrobats, some (e.g., Northern Mockingbird) mimicking all manner of other bird sounds, others (e.g., Brown Thrasher) inventing sounds on the spot from whole cloth. This species does some of both, but he differs from those two familiar species in the way he presents his sounds. The Brown Thrasher produces couplets of phrases, while the Northern Mockingbird usually repeats a phrase multiple times before moving on to another motif. The California Thrasher often produces a rather long mixture of muliple phrase-types, then pauses for a while before doing the same again. This is the typical mode of singing of the other western North American thrashers as well. Regardless, it is entertaining to listen to, for the oddity of some of the sounds, as well as their organization into stanzas.

Two other things, if you don't mind: chaparral and the Least Bell's Vireo. Chaparral is a plant community dominated by woody shrubs with thick (drought-resistant), evergreen leaves, including the satiny-barked manzanita. This kind of vegetation grows in places with hot dry summers and mild moist winters. Such Mediterranean climates are typically found on the southwestern corners of continents, as well as around the Mediterranean Sea, and the chaparral-equivalents (different species with the same physiological characteristics) in those lands have evocative names, such as maquis, fynbos, and matorral. Occasional hot fires are a regular part of these plant communities, but the shrubs readily send up new shoots from the roots, which survive the fires.

A recording of the Least Bell's Vireo may be accessed through the Ebird checklist. This endemic subspecies was down to a few hundred pairs because of loss of habitat (riparian brush, which was never abundant to begin with). The population was classified as endangered. Control of cowbirds (brood parasites that devastate vireo populations) and habitat managment have helped the Least Bell's Vireo bounce back from the brink of extinction, but its small range and rare habitat make it intrinsically vulnerable.

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