A small lizard found only on four islands off the southern California coast is being taken off the federal Threatened Species list. According to the U.S. Fish and Wildlife Service, the island night lizard (Xantusia riversiana) has rebounded in numbers, with threats to the species lessened significantly since the lizard was first listed as Threatened in 1977.
The island night lizard, which grows between 5-8 inches long, is found only on San Clemente, San Nicolas, and Santa Barbara islands off the California coast, along with Sutil Island, a 14-acre islet half a mile from Santa Barbara Island.
When it was listed, the night lizard was under siege by introduced predators such as feral cats and rats, and introduced grazers such as feral goats and rabbits were devouring the lizards' preferred habitat. According to USFWS, though, those threats have been countered, as have the invasive exotic plants that displaced the lizards. The agency now says the lizards now number in the millions.
It hasn't hurt that all of the islands the night lizard calls home are owned by the federal government. San Clemente and San Nicolas islands are owned and managed by the U.S. Navy, while Santa Barbara Island and its tiny neighbor Sutil Island belong the the National Park Service. That's simplified tasks such as removing introduced predators and yanking out weeds.
In 2004, the Navy petitioned USFWS to delist the lizards on San Clemente and San Nicolas islands, claiming that each island's population was properly considered a Distinct Population Segment (equivalent to a species under the Endangered Species Act) and saying that the population of night lizards on each of the two islands had recovered.
That prompted a 2006 status review for the lizard, and in February 2013 USFWS finally got around to its response: a proposal that the lizard be delisted throughout its range. With this new ruling, scheduled for printing in the Federal Register on April 1, that delisting becomes official.
According to USFWS, estimates of the lizard's current population range from 15,300 on San Nicolas and 17,600 on Santa Barbara/Sutil, with an astonishing 21.3 million estimated for San Clemente Island. The estimates didn't count lizards, but merely assessed the acreage of lizard habitat on each island and used mathematical models to extrapolate estimated total populations.
At least one of the reviewers that commented on the delisting proposal in 2013 challenged the delisting, saying that the lizards and their habitat on San Nicolas Island were far from secure, and suggesting USFWS either retain the San Nicolas Island population or the entire species on the Threatened list. Other commenters suggested that a looming threat to the lizards, climate change, hasn't been ameliorated.
USFWS pointed to the night lizards' varied and omnivorous diet to suggest that the lizards might well be able to adapt to climate change. The agency ruled that despite a smaller population and less suitable habitat on San Nicolas Island, the lizard had nonetheless recovered to the point where it no longer meets the legal definition of "Threatened."
That varied and omnivorous diet that's helping USFWS feel better about the island night lizard's diet in a warming world includes insects, other small animals, and plant matter -- which makes up as much as half of some island night lizards' stomach contents. Though some of the night lizard's mainland cousins are among the smallest lizards in North America, the island night lizard -- freed from predation by larger animals as it evolved on the island -- is significantly larger. Individual island night lizards have been known to live 25 years or more in the wild. Despite their common name, night lizards are generally most active during the day, though they do tend to spend their days hiding under tree limbs and other objects. In the case of San Clemente Island, those objects apparently include decaying sheets of plywood discarded by Navy workers.