Not just seals

January 21, 2013

Although our main study efforts during the winter season on Southeast Farallon Island (SEFI) revolve around the Northern elephant seals and their breeding season, there are a number of other long-term monitoring studies that garner our attention. These range from bi-monthly arboreal salamander surveys, weekly cricket and burrowing owl pellet surveys, daily bird monitoring for new arrivals and non-breeding species and cetacean watches.

Farallon Arboreal Salamander (Aneidis lugubris farallonensis) Surveys

The Farallon salamander is considered a sub-species of Aneidis lugubris, which is found along the coast of California. The Farallones were once connected to mainland California over 10,000 years ago and the salamander has hitched a ride over the years and is the only native terrestrial vertebrate species on SEFI. The species is described as arboreal because of its ability to climb trees. It has large toe tips and a prehensile tail which is adapted for climbing.

Adult Farallon Arboreal Salamander

Two salamanders found under the cover boards

However, on the island we have a severe shortage of trees so the salamanders have adapted to live around rocks which provide cover from potential predators and a damp dwelling. PRBO biologists have distributed over 500 cover boards which are used both to provide burrowing habitat and to permanently mark study plots.

Adult and juvenile cover boards

There are two salamander studies currently taking place on SEFI, a population dynamics study started in 2006 and a population distribution study which started in 2012.

The 2006 study is focused on the northwest section of the island and is conducted every 2-weeks and involves 156 cover boards. For the study we measure, weigh, and sex individuals by looking for eggs in a female’s translucent belly or the male’s distinctive mental gland under the chin, which is involved in pheromone production. These metrics are used to understand age at maturity and reproduction rates.

Ryan measuring the snout-to-vent length of a ‘mander

Yellowish eggs can be seen in the underside of adult female salamander

We also take pictures of both the left and right sides of all salamanders that are over 30 mm. Each salamander has a unique spot patterns much like finger prints on humans which allow biologists to track them over time and understand survival rates. The photos we take are added to a database created for long-term mark-recapture monitoring.

The 2012 study is an island wide study conducted once a month and involves over 400 cover boards. For this study we only measure salamanders less than 45 mm to understand the population structure and habitat use of salamanders across the island and to increase our detection of juvenile salamanders – an important component in understanding population dynamics. We typically find many of our salamanders in northwest facing areas due to the limited exposure of the sun and favorable loamy soil rather than the sandy substrate we find on the south and east facing sides of the island.

Farallon Cricket (Farallonophilus cavernicolus) Surveys

The Farallon Cricket (Farallonophilus cavernicolus) was first described by David C. Rentz in 1972. It is a member of the Rhaphidophoridae family which includes the cave weta, cave cricket, camelback cricket, camel cricket and spider cricket. Cave and camel crickets are both quite abundant in California. One of the most interesting natural history facts about the Farallon cricket is that it is the only truly endemic species on the Farallones, this species is not found anywhere else in the world!

Adult, juvenile and immature crickets on cave wall

The cricket study started on the island in 2012 and involves five main study plots which are either caves or the outside rock faces of caves. This study is being used to better understand the natural history of the species since there have been very little research efforts dedicated to the cricket.

One of the cricket study plots. The pink dots mark the boundaries of the plot.

Western Burrowing Owl (Athene cunicularia hypugaea) Pellet Surveys

One of the more odd species that we find on Southeast Farallon Island is the western burrowing owl (Athene cunicularia hypugaea), a subspecies that ranges from Canada, through the Midwest and into Mexico. In California, the burrowing owl is a Species of Special Concern, and it is an endangered species in Canada. The burrowing owl population has long been in decline throughout much of its range. These small owls (10 inches tall and 1/3 pound) are terrestrial owls, typically associated with flat grassland, open fields, and with medium-sized burrowing mammals such as ground squirrels or prairie dogs. However, on the island we have none of those species other than the introduced Siberian house mouse, and there is also no flat grassland but an open ocean with 30 miles between the island and mainland. The U.S. Fish and Wildlife Service and PRBO biologists have been monitoring the burrowing owls on the island for the last few years, especially their feeding behavior. During the late spring, summer and fall the owls typically feed on the Siberian house mouse however as temperatures drop and the rainy season arrives the mouse population plummets and the owls switch over to feeding on Ashy Storm Petrels which come in to roost. The owls typically will rip the wings off the storm petrel and consume the whole body.

Western burrowing owl peering out of its roost

During the winter we conduct roost checks once every week looking for owl pellets. There are approximately fifteen roosts scattered throughout the island that we check. The pellets are bagged and frozen and then sent to a lab for analysis. Many of the roosts are located on lighthouse hill which offers some fun climbing adventures searching for the pellets.

Owls roosts on Lighthouse Hill correspond with Pigeon Guillemot nest markings. Notice the yellow numbers written on the rocks.

Pellet found on Little Lighthouse Hill

Island ecosystems are particularly interesting to study because of their sensitivity, such as the impact that introduced species can have. The Siberian house mouse is thought to have arrived with Russian sealers in the 1800s and the burrowing owls are here partly because of the mice. Conversely, the Farallon Islands are the largest roosting site for Ashy Storm Petrels in the world and the owls are not a typical predator of the petrel. With the species population currently unknown and the important role that the Farallones play in the reproduction of the Ashy Storm Petrel, the burrowing owls can have a very significant effect on the Ashy Storm Petrel population. Western burrowing owl populations are also in decline, however it is believed without mice the owls could not survive on the Island.

Cetacean Watches

One of perks of living on a remote island in the middle of the ocean is observing the marine life that inhabits the area. Though the species will differ throughout the year, the Farallones offer a great vantage point to observe migrating humpback, grey and blue whales as well as killer whales, Risso’s and Pacific white-sided dolphins. Currently we are in the midst of the southern migration of grey whales which are traveling from Alaska to their calving grounds off Baja.

Grey whale seen from the lighthouse

Two grey whales feeding in Mirounga Bay

As we conduct our work around the island we often see the blow of whales traveling south. There are also six resident grey whales that call the Island home. It is common to see whales feeding within 100 meters of the shore. During one of the Patrol runs a resident grey whale passed between the east landing buoy and east landing offering a good glimpse for our visitors. On clear days we typically conduct a three hour cetacean survey from the lighthouse. The goal of these surveys is to monitor the grey whale species as it travels south. These watches are staffed by two people; each person is on watch for 1.5 hours, switching from viewing the north and south side every 15 minutes. Our current high count for a 3 hour period is 57 grey whales (51 traveling, 6 residents).

Blow of a grey whale seen from shore

Flat, clear day. Perfect for a cetacean watch.

Resident grey whale feeding around the North Landing buoy

We also monitor shipping traffic as the San Francisco area has many busy ports and the risk of vessel strikes is high. In late-2012 a proposal was adopted by the International Maritime Organization (IMO) to improve navigational safety and to reduce ship strikes on the approach to San Francisco Bay, the Santa Barbara Channel and the Ports of Los Angeles and Long Beach.

https://sanctuaries.noaa.gov/news/press/2012/pr122712.html

In 2007, shipping lanes were shifted in Stellwagen Bank National Marine Sanctuary, off the coast of Massachusetts. The area is a popular feeding ground for humpback and the endangered North Atlantic right whales. The shipping lane modification has reduced the risk of ships striking whales by 81 percent. Hopefully the results will be as successful on the west coast!

Island Excursion

We recently had a stretch of great weather which we were able to take advantage of by taking out the SAFE boat for a trip around the island. It was really nice to get out on the water and see some of the species we have been observing from the Island up close. It also offered a nice break from our daily elephant seal work and gave us a different perspective of the island.