Even with powerful top-notch binoculars, it's not easy singling out the Southwestern Willow Flycatcher from other subspecies of a family of birds known collectively as Empidonax.
Expert bird watchers say positive identification of the drab birds with wing bars and pale eye rings depends on subtle differences in bill shape, habitat, song and wing and tail length.
Then there's Robert M. Zink, a professor of biology at the University of Minnesota, who says the bird scientists know as Empidonax traillii extimus is not a distinct subspecies and, therefore, should have its federal protections as a threatened subspecies removed.
A reanalysis of plumage coloration and genetic variation in mitochondrial and nuclear DNA found no support for the distinctiveness of the bird described as a subspecies in 1948, according to his peer-reviewed conclusions published this month in the ornithological journal the Condor.
"I suggest that the Willow Flycatchers of the Southwest represent peripheral populations of an otherwise widespread species that do not merit subspecific recognition," he said in the report, "and are therefore inappropriately listed as endangered under the Endangered Species Act."
In 2013, a separate analysis by Zink and George Barrowclough, associate curator of ornithology at the American Museum of Natural History in New York, reached a similar conclusion about the coastal California gnatcatcher, whose status as a threatened subspecies has barred development in many areas of prime Southern California coastal real estate for two decades.
The California Building Industry Assn., backed by Zink's research, has petitioned the U.S. Fish and Wildlife Service to delist that bird, which it argues is not a valid subspecies.
If the agency agrees, it could remove federal protections it extended to the small, blue-gray songbird in 1993 -- opening the way to development on thousands of acres of largely coastal land.
That land was designated as habitat for the California gnatcatcher after it was deemed a threatened species facing loss of habitat due to development, repetitive wildfires and invasive plants. Now, as California experiences its most severe drought in decades, "is a terrible time to be arguing about removing the protective status of any bird," Garrison Frost, a spokesman for Audubon California, said in an interview.
A recent analysis of Zink's genetic data by John E. McCormack, director of the Moore Laboratory of Zoology at Occidental College, and geneticist James M. Maley concluded that the data reflects an inadequate sampling of the gnatcatcher's genome and is not sufficient to overturn research to the contrary.
The Fish and Wildlife Service will make a final decision on the developers' petition later this year.