The Farallon Arboreal Salamander
February 10, 2010
The only native terrestrial vertebrate inhabiting the South Farallon Islands year-round is the arboreal salamander, Aneides lugubris. The Farallones population is considered a sub-species, A. lugubris farallonensis, but is closely related to arboreal salamanders at Point Reyes peninsula. The Farallones were connected to Point Reyes 10,000 years ago when sea levels were much lower.
On the mainland, this species is associated with oak woodlands. It is described as arboreal because of its unique ability and propensity among salamanders to climb trees: the enlarged toe tips and prehensile tail is adapted for climbing, and individuals on the mainland have been found in tree cavities as high as 60 feet above the ground!
However, trees are in rather short supply here on the Farallones – so what gives? Although its common name suggests that this salamander lives in trees, it is actually found mostly under rocks and logs and in crevices and burrows, and its arboreal tendencies may be somewhat overrated. Seabird burrows cover almost the entire Southeast Farallon Island and, together with the many rocks, provide abundant cover for salamanders.
One herpetologist noted that “this curious genus [Aneides] is furnished with by far the most powerful dentition of any existing salamander…” Given that the arboreal salamander is the biggest species of its genus, these guys have especially large and powerful teeth, and have even been known to bite the unsuspecting PRBO biologist!
Arboreal salamanders are lungless salamanders (family Plethodontidae) that breathe through their skin. This renders them sensitive to changes in water or air quality, making them good indicators of ecosystem health. PRBO biologists initiated a long-term monitoring study of the Farallon arboreal salamander in 2006.
In the dry season from May to October arboreal salamanders retreat to burrows deep beneath the ground where they guard their eggs and hatchlings and wait for the rains to return. They are only active near the surface during the winter rainy season. When at the surface they are strictly nocturnal, emerging at night to forage for beetles, isopods, and other insects. During the day they remain in stone walls and crevices and under rocks and boards.
We placed more than 100 permanent cover boards along the path from the PRBO house to North Landing. We check under the boards for salamanders every 2 weeks from November to May, the period of greatest surface activity. When we capture a salamander, we measure and weigh it, check for eggs (you can see eggs through their skin), and take photos of its spot patterns. Each salamander’s spot pattern is unique, so we can individually identify them using our photo database.
Unfortunately, a larger proportion of amphibian species are at risk of extinction than any other group of animals. Salamander populations throughout the world are threatened by chemicals, infectious diseases, and habitat loss. By studying the Farallon arboreal salamanders, we can understand their population dynamics and hopefully ensure a future for this special and unique creature.