Site visits are critical to helping scientists learn more about species and their habitats. The trips often take them into areas most people do not have a chance to explore, including public and privately-owned restricted sites, as well as some remote and hard-to-reach areas. “Site visit Insights” provides a behind-the-scenes perspective of wildlife biology, featuring photographs, and interesting discoveries and happenings biologists experience in the field.
In cooperation with the U.S. Fish and Wildlife Service, The Wildlife Society is pleased to share these insights.
Valerie Hentges, fish and wildlife biologist, Sacramento Fish and Wildlife Office
Site visit location:
Ohlone Regional Wilderness, Alameda County, California
What was the purpose of the site visit?
I was eager to join East Bay Regional Park District for a Central California tiger salamander (Ambystoma californiense) survey at the Ohlone Regional Wilderness’ higher elevation ponds to enhance my understanding about the life cycle of the threatened California tiger salamander. Learning and researching more about the species will help our efforts in their recovery. I always appreciate invitations to assist with research because it is a fantastic opportunity to learn more about a species I work with often.
California tiger salamanders spend the majority of their life underground in burrows created by other animals like ground squirrels and other burrowing mammals since they are poor borrowers themselves. After several years staying within their burrow system, they reach sexual maturity. Once the winter rains start in or around November, California tiger salamanders will leave their burrows in search of breeding ponds. Rainy and stormy nights are their favorite nights. Depending on the rainfall amounts during any given year and the timing of the rainfall, some may only be lucky enough to reach a breeding pond and successfully pass on their genetics once in their lifetime. If breeding is successful, eggs will hatch within two weeks. Although, a considerably longer timeframe is necessary to develop into their next life stage from a larvae to a juvenile. When sustained water levels in the breeding ponds support the larvae long enough to complete metamorphosis—depending on various factors such as seasonal water levels, food supply, temperature and oxygen levels—they will leave their pond in search of burrows for the long dry season and until they reach sexual maturity.
We are concerned for the species because of several threats to the population. The primary threat to their habitat is through fragmentation or loss due to development and some agricultural practices. Other species like non-native bullfrogs, fish and birds (i.e., egrets and herons) prey on California tiger salamanders. The loss of burrows created by ground squirrels, gophers or other burrowing mammals also affect them due to rodent control programs across the landscape limiting the number of burrows available. Without the burrows created by these mammals, California tiger salamanders have no place to call home. Prior to needing their underground home, they also need the timing of the rainfall to be suitable for the adults to lay their eggs in a pond. The larvae need water in their breeding ponds long enough to sufficiently develop into juveniles before the water evaporates. This allows them to move across the ground in search of a burrow, which can be challenging. Barriers, like housing, can trap them or vehicles can cause injury or death before they reach a burrow.
Where did you go?
The survey was conducted at the Ohlone Regional Wilderness. It is a 9,737-acre parkland managed by East Bay Regional Park District in Alameda County, California. Rose Peak is its highest point at 3,817 feet. The property has a few human residences and cattle grazing, but the remaining acres allow wildlife, including bald eagles, mountain lions, bobcats, mule deer and a herd of Tule elk to call the property home. This population of California tiger salamanders is mostly found in the vernal pools and seasonal ponds of the Coastal, Central Valley and Sierra Nevada foothills of California.
What partners were you working with and what is the nature of SFWO’s partnership with them?
Partnerships and local experts are key to the work we do to conserve the species. For this field day, our partners were East Bay Regional Park District and California Department of Fish and Wildlife. East Bay Regional Park District protects, manages and preserves the landscape for wildlife and allows people to take a break from urban areas to appreciate the natural resources. The California Department of Fish and Wildlife are our state partners managing and protecting the state resources of fish, wildlife, plants and their habitats.
What did you learn from this site visit that you didn’t know before?
Learning always comes in a variety of forms. Reading the scientific literature, for me, is half of the learning process. The other half the process is putting the pieces together from what I read into the analysis of the various projects I evaluate for the protection and conservation of species. Talking with and participating in field days with the local experts are, for me, the essential glue between these two processes.
One of these learning pieces I was able to see firsthand during this field day is the integration of good land management benefiting multiple species. Grazing on this property provides grassland management for a multitude of reasons, including benefits for species like the California tiger salamander. Several of the ponds we surveyed were within a grazing lease that allowed the ponds to have very little dense edge vegetation. The lack of vegetation could make it easier for California tiger salamander adults to reach breeding ponds.
On the other hand, the lack of edge vegetation could make it easier for predators to find them on their journey from breeding ponds to upland burrows. The goal is trying to find the correct balance. The longer it takes them to reach a burrow increases the likelihood of death, from drying out or predators. In addition, some land managers may think it is better not to graze near a pond for the fear of the closeness of and size of cattle in the same area that could crush these amphibians while they are in their developmental stages (larvae, metamorph and juvenile). However, this field day we saw more of the benefits of managed grazing. At one of the ponds, there were a lot of California toad metamorphs (Anazyrus boreas halophilus) and cattle at the water’s edge. When we surveyed, we verified several amphibian species using this particular pond. Another pond we sampled had tall vegetation along the pond’s edge, but it did not have the large numbers of amphibians like the pond that had cattle nearby or in the pond.
What surprises did you encounter during the site visit?
For this field day, the size and abundance of the California tiger salamander larvae in these ponds at the beginning the summer was a little surprising. California tiger salamanders, like many amphibians, require water for breeding and throughout their developmental life stages. In California’s Mediterranean-like climate, most rain occurs during the mild, wet winters. The rainy season prior to this field day started later than normal and there was less rain in most of the species’ range. The eggs deposited by California tiger salamander adults during the beginning of this winter, when there was little water left in the ponds, likely did not survive. Those that breed in late winter, when there was adequate and sustained water in the ponds, likely had more success.
The larvae we encountered on this field day should have been able to complete their development in the ponds in time to search for burrows or their underground home prior to the water evaporating in late spring or early summer. A tricky aspect for researchers is observing them prior to them leaving their breeding pond. Their very cryptic behavior makes it hard for us to learn more about this species, so being attentive to the environmental conditions allows us to conduct more research prior to them finding their burrows.
The U.S. Fish & Wildlife Service is a Strategic Partner of The Wildlife Society.
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