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Long Term Monitoring and Management of the Endangered Arroyo Toad (Anaxyrus californicus)

Calling Male Arroyo Toad

It is important that monitoring programs for endangered species provide valid scientific information to help in understanding species ecology, inform management, and provide feedback on the effectiveness of management actions.  This is vital for helping to ensure long term persistence of the species. Spatial programs can be ideal for generating this information due to their power to model landscape and environmental covariates in relation to the presence of species across the landscape.  

The arroyo toad is a specialized amphibian endemic to the coastal plains and mountains of central and southern California and northwestern Baja California.  It primarily inhabits low gradient streams and rivers comprised of sandy soils and containing sandy streamside terraces. Reproduction is dependent on availability of shallow, still, or low flow pools in which breeding, egg laying, and larval development occur. Currently, this species only occupies an estimated 25% of its previous habitat within the United States.  

Since 2003, we have conducted an occupancy monitoring program for the endangered arroyo toad on Marine Corps Base Camp Pendleton (MCBCP), California.  The arroyo toad populates three of MCBCP’s major watersheds:  Santa Margarita, San Onofre, and San Mateo.  These watersheds support the only known remaining coastal populations of the arroyo toad in the United States.  This program has also been extended to a long term study area in Warner Springs, California.

The San Diego Field station has been conducting studies on arroyo toad ecology across southern California since 1999.  In addition to long-term monitoring programs, we study the responses of arroyo toad populations to disturbances such as fire and to changes in hydrology from dam operations.  We are also using radiotelemetry to understand seasonal movements of arroyo toads and their use of flood plain and upland habitats.

Project Details

In 2002, we developed a long-term monitoring protocol for the arroyo toad in collaboration with a scientific panel of species experts, amphibian ecologists, and statisticians.  We employ a spatial and temporal monitoring approach that tracks the presence breeding populations by documenting the presence of eggs and larvae.  We use the log-linear modeling program, PRESENCE, to calculate annual estimates of proportion area occupied (PAO), as well as the probabilities of detection, colonization, and extinction over time.  Sites are surveyed up to four times per year to calculate and account for imperfect detection probabilities.

Multi-year occupancy models show that arroyo toad population dynamics differ according to hydrology. Population dynamics within ephemeral stream systems are highly variable and driven by stochastic processes (i.e. amount of rainfall), while those in perennial stream and riverine systems are more stable and likely driven by deterministic processes (i.e. predation, competition, habitat alteration). In these perennial systems on MCBCP, detection of toad larvae is consistently negatively associated with the presence of non-native aquatic species. Currently, we have an active feedback loop with arroyo toad monitoring results and aquatic invasive species management, and the Base is actively working to control non- natives within arroyo toad habitat

Other studies have shown positive responses of arroyo toads to habitat disturbance from floods and fires, which help keep the open habitat suitable for this species.  Simulation of natural flood events and seasonal availability of water are important considerations for management of the toad on dammed waterways. 


The objectives of these programs are 1) to better understand the spatial and temporal dynamics of the endangered  arroyo toad , 2) to detect and identify causes of positive or negative trends, and 3) to inform and maintain a feedback loop between monitoring and management of the arroyo toad.

USGS Contact For This Project
Robert Fisher
(619) 225-6422
San Diego Field Station
4165 Spruance Road Suite 200
San Diego, CA 92101
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