Island Life for Salamaders

Arboreal Salamander on Log

This story by PRBO Conservation Science Biologists Russ Bradley and Ryan Berger was originally published in the Summer 2011 issue of Tideline, the quarterly newsletter of the San Francisco Bay National Wildlife Refuge Complex.

Sharing its origins with the core of the Sierra Nevada Mountains, the Farallon Islands were violently shaken free from the mainland some millions of years ago. In the ensuing years the Farallones have drifted northwest as a result of movements from the Pacific Plate and currently reside 27 miles west of the Golden Gate and 18 miles southwest of Point Reyes. The Farallon National Wildlife Refuge provides habitat for a great assortment of wildlife. Hosting the largest seabird colony in the contiguous United States, the islands provide nesting grounds for over 300,000 breeding birds. In addition, large numbers of seals, sea lions, and white sharks frequent the islands and their adjacent waters. Many winged migrants, like song birds and even bats will stop over on the islands during their travels.

We at PRBO Conservation Science, in partnership with the U.S. Fish and Wildlife Service, have been conducting monitoring, research, and stewardship efforts on the refuge for over 40 years. Until recently, our work has focused almost entirely on animals which either fly or swim their way to the islands. However, recently we have started study of an unlikely Farallon inhabitant - the Farallon Arboreal Salamander - that hitched a ride on the islands’ slow but steady drift northward on the Pacific Plate after the islands were separated from the mainland. 

Arboreal Salamander Showing Long TailThe arboreal salamander, Aneidis lugubris, is endemic to California and Mexico, occurring in coastal and interior oak forests, but also on islands, from Humboldt County, CA to northern Baja California. This group of salamanders has no aquatic larval stage - eggs are laid in terrestrial nests and hatchlings resemble miniature adults. Females will lay their eggs on the underside of moist damp places – like decaying trees on the mainland, or under rocks in damp areas of the island. They are primarily nocturnal, foraging for small prey such as spiders, beetles, grubs, ants, and centipedes on the ground or on the trunks of trees. During the day they remain under rocks, decaying logs, and in stone walls and crevices. Arboreal salamanders are unusual in that they have enlarged toe tips and a prehensile tail adapted for climbing, which serves them well in their habitat on the mainland. However, this adaptation may not fare so well on the Farallones, seeing that trees are few and far between. Arboreal Salamanders are more tolerant of dry conditions than other lungless salamanders, and are often the last species to retreat beneath ground when the dry season begins. Lungless salamanders conduct respiration through their skin which requires them to live in damp environments on land, not in water, and to move about on the ground only during times of high humidity. 

The arboreal salamander is the only native terrestrial vertebrate inhabiting the Farallon Islands. The distinctive spot pattern of the salamanders on the islands led Van Denburgh (1905) to consider the population as a sub-species A. lugubris farallonensis. PRBO biologists have been checking for the presence of salamanders bimonthly since 2007 under cover boards, which are used both to provide burrowing habitat and to permanently mark study plots. Arboreal salamanders exhibit high site fidelity, and we often find the same animals under particular cover boards. Individuals are measured, weighed, and sexed by looking for eggs in a female’s translucent belly or the male’s distinctive mental gland under the chin, involved in pheromone production. 

These salamanders possess unique spot patterns much like finger prints on humans which allow biologists to track them over time. A photo database of captured salamanders has been created for longterm mark-recapture monitoring. Some individuals are quite easily distinguishable by anomalies such as missing limbs or extra digits. Salamanders are common on the island starting in late fall, when the first rains come, and disappear underground in the summer when the soil dries out.

A recent report and publication based on Farallon salamander data has been completed, led by Derek Lee, our former PRBO winter biologist who initiated Southeast Farallon Island this study. This research has made some fascinating discoveries. We have found that the species has a delayed maturity, with an average age of breeding maturity of three years. Adult survival was high, with 78-88% of adults surviving from one year to the next. Using size data to compare with other salamander species, we estimate that Farallon salamanders can be very long lived, with average adult life spans of eight to eleven years. Amazingly, these parameters resemble those of seabirds like Cassin’s Auklets, and those of Northern Elephant Seals. 

So why is it important to study these wet, slimy amphibians that spend much of their time underground? Many salamander populations around the world currently are
experiencing threats from chemicals, infectious diseases, global warming and increasing climatic variability. In particular, arboreal salamanders are lungless and offer unique attributes that make them good indicators of ecosystem health. Breathing through moist, well-vascularized skin makes them vulnerable to changes in water or air quality. Baseline demographic data are helpful in documenting effects of existing and future threats to salamander populations – particularly unique ones like we have here on the Farallones. By obtaining data now and continuing to monitor into the future, we can better manage salamander populations on the island and hopefully be able to use these salamanders as another indicator species of ecosystem health. 

Russ Bradley is the Farallon Program Manager for PRBO Conservation Science. Originally from Vancouver Island, Canada, he completed his Bachelors and Masters  degrees in Biology from Simon Fraser University in Vancouver. This year will be his 11th field season on the Farallones, where he has spent over 1200 days in the field working with PRBO’s long term seabird ecology studies.  

Ryan Berger just completed his first season as winter Farallon Biologist from PRBO. Ryan got his Bachelors degree from the University of Illinois and his Masters from Georgia Southern University. Before coming to work at PRBO, Ryan coordinated marine mammal research and standing response for the Florida Fish and Wildlife Conservation Commission PRBO Conservation Science in Jacksonville.