Author: Damien M. Schiff
On Tuesday, we announced the filing of a petition with the United States Fish and Wildlife Service to delist the California gnatcatcher from the Endangered Species Act. In this post, I'd like to go into a little detail as to why the gnatcatcher should not be a listed subspecies.
In 1993, the Service listed the California gnatcatcher as a threatened subspecies. In determining that gnatcatchers represented a valid subspecies, the Service relied on a study by Atwood (1991). Since 1993, several published studies have concluded that the Atwood subspecies classification is invalid and that the California gnatcatcher should be considered an undifferentiated part of one species ranging from Southern California to the southernmost tip of the Baja California peninsula in Mexico.
In that study, Atwood concluded that the California gnatcatcher subspecies classification was justified in light of observed changes in certain morphological characteristics (i.e., plumage coloration and body size) in collected gnatcatcher specimens from various locales. Studies published by Zink, et al. (2000), and Skalski, et al. (2008), have determined that Atwood (1991) was wrong on at least three points.
1. Zink, et al. (2000), determined that Atwood's observed morphological characteristics changes are not representative of genetic differentiation. In their paper, Zink and Atwood expressly state that P. californica should have no subspecies.
2. Skalski, et al. (2008), determined that Atwood’s statistical analyses were seriously flawed, because Atwood’s supposed diagnostic characters support a geographic cline, not a distinct break in character distribution markers, which break could support a subspecies classification.
3. Skalski, et al. (2008), determined that Atwood’s data sets were confounded: many of Atwood’s specimens may not have been representative of wild gnatcatchers.
Thus, in terms of morphological, statistical, and genetic data analysis, the Atwood (1991) subspecies classification for the California gnatcatcher is not valid. New science (Zink, et al. 2000) also indicates that the California gnatcatcher does not qualify as an evolutionarily significant unit, and instead should be considered part of a single species of gnatcatcher whose range extends from southern Baja California, Mexico, to Southern California.
Under the ESA, the Service has 90 days to issue an initial finding on our petition. Here's to hoping that the Service recognizes the flawed taxonomic basis of the 1993 listing.