U.S. Fish & Wildlife Service

Sacramento Fish & Wildlife OfficeServing the people, conserving the fish, wildlife, and plants of California

A Unit Of The Pacific Southwest Region

Building a Bank Takes More Than Just Snakes

May 19, 2011

In an area surrounded by rice fields and flanked by the Sutter bypass, there is a small but fertile area filled with water and plant life, but there are no crops growing here.  This land has become a home dedicated to the giant garter snake.

The spot in question is the 429-acre Sutter Basin Conservation Bank, created by Westervelt Ecological Services in 2008, and according to U.S. Fish & Wildlife Service Biologist Dwight Harvey, "this bank has become one of the best examples of created habitat for the giant garter snake in the Sacramento Valley."  What was once agricultural land in an area surrounded by rice and other crops has become much more than that.

Giant Garter Snake

Photo courtesy of Westervelt Ecological Services

Listed as a threatened species by the U.S. Fish and Wildlife Service in 1993, the giant gartersnake inhabits agricultural wetlands and other waterways such as irrigation and drainage canals, sloughs, ponds, small lakes, low gradient streams, and adjacent uplands in the Central Valley.

Because of the direct loss of natural habitat from agriculture and development, the giant garter snake relies heavily on rice fields in the Sacramento Valley, but also uses managed marsh areas in Federal National Wildlife Refuges and State Wildlife Areas. Snake habitat tends to be areas where there is a mixture of wetland and upland, foliage and open space, where there is both water and cover available.  Unfortunately, this puts the snakes into harm's way when the fields are worked over by tractors and people.

Sutter Basin Conservation Bank

Photo courtesy of Westervelt Ecological Services

This is where the idea of a conservation bank becomes useful. Starting in the early 1990's, conservation banks are like financial banks, protecting resources like a bank protects people's money. When a company or individual plans a project that will impact endangered species or other natural resources, they may buy credits at a conservation bank in order to offset any impacts. The bank owner then uses the money to protect and manage the resources within the bank. 

Traditionally, project developers have been asked to preserve part of the area they are developing. Sometimes this is a good policy, but generally it is better for the species to have larger areas protected and conservation banks are a good option for that. 

It is also more efficient and cost effective to manage a bank instead of small, isolated properties. By providing an alternate habitat that is free of the dangers associated with other areas where the snakes found, researchers can monitor these created wetlands and adapt the management of them so the snakes will inhabit these set-aside areas and thrive once again.

One of the first giant garter snake conservation banks in the Sacramento Valley was the Pope Ranch Conservation Bank, located in Yolo County.  Constructed in 2001, it employed a simple design of three narrow channels that meander through three separate fields.  Since then, the understanding of the habitat preferred and needed by the giant garter snake has evolved and changed to incorporate new ideas and research. 

"With each conservation bank something new is learned about the species and about how the snakes interact with their environment," Harvey commented.

Aerial photo of Sutter Basin Bank

Photo courtesy of Barnett Environmental Services

The Sutter Basin consists of six canals of varying lengths, allowing each canal to be drained separately in order for maintenance crews to allow for cleaning of the channels and reduction of marsh biomass to provide more foraging habitat for the snake.  This allows the snakes to relocate to another area within the bank when required maintenance is done.

The bank also alternates between wetland and upland, foliage and open space, to accommodate the snake's needs on a year-round basis, and uses a mixture of irrigation and well/ground water to balance out the levels of nutrients and contaminants found in both. Surface water is the primary water source with well water used to supplement the marsh when irrigation water is scarce or of poor quality.

Much has been learned by each successive bank, from amount and source of water, the mixture of highland to wetland, location and size.  "This is as much about what does not work as what does," points out Harvey,  "Each of the close to a dozen banks located within California have been learning from and bettering what came before."

Approximately 2400 total acres of habitat have been recreated for the giant garter snake, with each bank averaging in size of about 200 acres each, and each incorporating new layouts and differing mixes of habitat areas for the snake.  "The feedback from site monitoring and on-the-ground habitat management experiences over the last several years has greatly contributed to the evolution of habitat restoration design and management activities for this species," added Matt Gause, senior ecologist with Westervelt Ecological Services.

With all conservation banks, location is very important.  The site needs to be in a known area inhabited by the species.  What seems to have made the Sutter Basin Bank such a success so far is both the mixture of habitat within the bank and the use of both irrigation and well/ground water, and how each of these aspects are mixed together within the whole.  Instead of two or three habitat-specific areas within one bank, Westervelt decided to take a more natural approach to the planning of the bank as a whole, and so far the snakes are loving it.

"Banks are a conservation tool and a recovery tool," says Sacramento Fish and Wildlife Office's Assistant Field Supervisor Ken Sanchez.  "Conservation banks have been used as a means to slow the loss of habitat, not only for the giant garter snake, and to provide benefits to a number of other species of concern to the Service."

These include waterfowl, the western pond turtle, tricolored blackbird, the white faced ibis and a number of other egrets and herons who will nest in the same habitat as the giant garter snake. The true test will be over time; as the amount of knowledge acquired between the construction of the Pope Ranch and Sutter Basin banks has led to new and exciting ideas of how best to create and manage a habitat for the snake, so too will time show the relative merits of conservation banking, and the effects upon the species they aim to protect from extinction.

For now though, the giant garter snake seems content to rest along the bank of a shallow canal filled with water to drop in to when it senses danger, a place to escape the hazards of people and vehicles and just warm itself on a rock in the sun.  Sutter Basin Conservation Bank is a habitat worth calling home.

Story by Aaron Cotter, Volunteer, Sacramento Field Office

Last updated: November 9, 2017