Photo: Stuart Allen's Lake Berryessa Line

The Putah-Cache Bioregion Project:

Terrestrial Biomonitoring,
Spring '97-Winter '98

Who | What | Where | Publications

Graduate Coordinator: Melanie Allen Truan, mltruan@ucdavis.edu

Site Summary
Avian Survey
Small Mammal Survey
Vegetation Survey
Aquatic Funnel Trapping
Pitfall Trapping
Photography and GIS
Outreach
Future Directions

Site Summary

Field work occurred at six sites along lower Putah Creek. Sites were chosen for their ecological interest, their accessibility, and their conservation and/or restoration potential. For each site, four 100 m. transects were delineated, running parallel to Putah Creek and incorporating as much representative habitat as possible. All subsequent animal and plant surveys took place along the same transects.

Avian Survey

UC Davis undergraduates conducted weekly surveys of resident and migratory avian species in the spring and fall of 1997, using point count and linear transect methods. Data include type of species and number of individuals, distance from bird to observer, method of detection, and habitat information. Ornithologists John M. Eadie Ph.D and A. Sidney England Ph.D assisted in training the surveyors.

Preliminary Results:
Summary statistics have been generated on avian species richness, abundance, and percent invasive species over the six sites.
Avian diversity: inversely related to levels of disturbance and degree of habitat loss.
Percent invasive species: directly related to levels of disturbance and degree of habitat loss.
Total abundance: sometimes directly related to disturbance, usually caused by a greater number of individuals of invasive species.

Small Mammal Survey

Mark-recapture surveys of small mammals were conducted at three of the six study sites in the spring and summer of 1997. Sherman live traps were baited and left overnight at 10 meter intervals along the transects. (Only three sites were sampled due to the potential for trap theft at the other three sites.) Captured animals were identified, sexed, measured, and ear-tagged before release. Douglas A. Kelt, Ph.D, provided guidance.

In spring, very few small mammals were captured. Nonnative rats and mice of family Muridae were the most common. In late summer, small mammals (especially native species) were somewhat more abundant, though sample sizes were too small to be statistically significant.

Since all the survey sites had been flooded the previous winter, we hypothesized that this pattern may have been caused by flooding-induced mortality and/or emigration followed by slow dispersal back into the riparian corridor. The nonnative rats and mice may have been able to escape into human habitats more readily, or to disperse more quickly into the riparian corridor from adjacent human-associated populations.

Thus areas of riparian upland refugia may be important to maintaining native small mammal populations, providing them safe harbor during times of prolonged flooding. These upland refuges appear to be relatively sparse in the Putah Creek corridor, due to agriculture and development immediately adjacent to the creek. More research is needed to ascertain whether this hypothesis can be supported.

Vegetation Survey

Objectives: A team of undergraduates conducted a summer vegetation survey of the six study sites. Detailed data on the herbs, shrubs, and trees growing within the riparian corridor were collected. Surveyors were led by Deborah Elliot-Fisk, Ph.D.

Results: Data are awaiting further quantitative analysis and research.

Aquatic Funnel Trapping

Objectives: A two-week preliminary survey of one site, using floating funnel traps, was performed in the summer of 1997. The traps had been designed primarily to capture aquatic snakes, such as the giant garter snake (Thamnophis gigas).

Results: Although no snakes were captured (we probably did not have enough traps to achieve habitat saturation), we did capture many nonnative centrarchid fishes, crayfish, and a preponderance of bullfrog larvae, giving us an idea of the predominant near-shore species at this site. Indeed, bullfrogs, which are well known to have major impacts on aquatic and riparian communities, appear common along lower Putah Creek.

Pitfall Trapping

Sampling for terrestrial invertebrates, amphibians and reptiles was attempted using pitfall traps connected by drift fences.

Results: Although some data was collected, primarily on terrestrial arthropods, this method was extremely labor-intensive and relatively unreliable. Except for juvenile western fence lizards, (Sceloporus occidentalis) whose wide-ranging habits resulted in their frequent capture, most of the reptiles and amphibians we observed were a result of visual searches--or simply of happenstance. We once caught a juvenile gopher snake (Pituophis melanoleucus) in one of our small mammal traps! Future survey efforts for reptiles and amphibians will likely consist of visual surveys at appropriate times of the year.

Photography and GIS

A collection of 35 mm color slides is being compiled, documenting our activities along the creek, including photographs taken during an aerial reconnaissance of the Putah Creek watershed. This collection has already proven useful for outreach programs and lectures.

Last quarter, as part of a course project requirement, Melanie Allen Truan and her undergraduate classmate Jennifer Kampbell created a GIS detailing Avian Species Biodiversity and Habitat Structure for three of the study sites.

Outreach

Last summer, the project sponsored two high school students, training them in environmental field techniques, through the UC Davis JASRAP program. We also presented a half-day workshop on field research and biomonitoring methodology to students attending the 4-H State Leadership Conference. In addition, we have provided recommendations and assistance to the UCD Arboretumís CREEKWATCH program and to the UCD Public Service Research Programís Eco-Ed program.

We have also been collaborating with the social science and cultural history component of the Putah Cache Bioregion Project. Some of the work recently published by PCBP Artists and Writers-in-Residence was produced as a result of our project-sponsored field trips.
Go to more on bioregion art.

Future Directions

Training for the spring 1998 avian survey is currently underway. Another small mammal survey is currently underway, designed to test the upland refugia hypothesis. In addition, a large mammal component is being planned for summer 1998, consisting of track plate methodology.

The Cache Creek Conservancy board are supportive of extending the survey and biomonitoring techniques of the Putah Creek study to Cache Creek.

Ph.D dissertation research projects are currently in the design phase, informed largely by results obtained from our survey and biomonitoring efforts. Projects will test the riparian upland refugia hypothesis, as well as a larger theory proposing the existence of interspecific facilitation between colonizing invasive plant and animal species in riparian communities.

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