Once abundant, Yosemite toads (Anaxyrus canorus) now occupy less than 50 percent of their historical range. Climate change impacts, such as low snowfall, higher temperatures, and fires have altered toad phenology and spatial/temporal connectivity among seasonal habitats. At ‘Toad Island’ Yosemite toads had not been observed since the 2013 Rim Fire, though there was previously a healthy population. To aid species’ recovery and develop reintroduction methodology, the park embarked on a pilot project to re-establish Yosemite toads at Toad Island. In 2022, we collected tadpoles from 3 robust populations and the San Francisco Zoo successfully headstarted a reintroduction cohort. In June of 2024, we released 118 adults to Toad Island. To understand dispersal, micro-habitat use, and survivability, we fitted 30 toads with radio-transmitters and tracked their movements from June-September; we performed visual surveys weekly to monitor un-tagged toads. Here we present initial findings, including movement, morphometric, and predation data, as well as ‘lessons learned’ from the 2024 pilot.

The red-belled newt (Taricha rivularis) is a poorly studied endemic California salamander species that can be commonly found along the coastal forests north of Sonoma County. In 2009, a disjunct population of red-bellied newt was discovered 130 km south of its previously known range. Here we document the range and breeding phenology of this population as of 2019 and contrast its habitat use with that of other sympatric newts. Surveys across two years suggest that the southern population of T. rivularis is confined to one 1-km reach of Stevens Creek and a tributary informally called Twitty Creek, and the population follows an early-March to late-April migratory breeding pattern. Spatial analysis shows that breeding male T. rivularis aggregate only in Stevens Creek, likely dispersing through Twitty Creek, and that they associate with riffle and run mesohabitats rather than pools. Sympatric T. granulosa and T. torosa populations tended to associate more with woody debris cover types and cobble substrates than T. rivularis. T. rivularis oviposition site selection was most influenced by large substrate size. Protecting large substrate and complex instream habitat in sensitive breeding reaches, as well as upland habitat along dispersal routes, should be an important consideration for land managers. Understanding the nuances of range, temporal behavior, and habitat needs for this disjunct population is critical to ensure the survival of this California Species of Special Concern.

In California vernal pools, both California Tiger Salamanders (Ambystoma californiense) and predaceous diving beetle larvae (family Dytiscidae) serve as top predators, playing key roles in shaping aquatic ecosystems. Through mesocosm experiments, we aim to investigate whether salamander larvae face higher mortality in the presence of predaceous diving beetle larvae, the predation rates between them, and how size disparities between these two predators may affect these interactions. Additionally, we seek to deepen our understanding of trophic dynamics in these ecosystems. As vernal pools continue to decline due to habitat loss and degradation, understanding these predator-prey interactions is essential for informing conservation efforts and managing the cascading effects of species interactions.

Sexual maturity is the point in an individual’s life history that demarcates the preparation for passing on heritable traits from being capable of passing them through sexual reproduction. Earlier age at sexual maturity confers a higher probability of surviving to pass on genetic material; and higher fitness because offspring are born sooner and potentially reproduce sooner. Age at sexual maturity is a trait that profoundly influences the intrinsic growth rate and is integral to predicting the demographic performance of animal populations. Understanding demographic performance allows wildlife managers to assess the relative success of translocations when restoring populations of imperiled species. Observations made of a marked population of California red-legged frogs in the years preceding their translocation to a neighboring county compelled us to reassess published statistics of their age at first reproduction. Informed by our observations, we anticipated that California red-legged frogs are capable of reproducing at an earlier age than previously reported. We translocated 6 egg mass halves over three years and observed several egg masses at the recipient site in the second winter of the project, confirming our observations from the donor site: that at least some California red-legged frogs are capable of sexual reproduction at a younger age than previously reported.

The web-toed salamanders (Hydromantes) have long been of interest to biogeographers due to their enigmatic distribution—southern Europe and California. In recent years, populations of Hydromantes have been discovered in increasingly unexpected settings, causing us to question our concept of what constitutes suitable habitat. Among these are populations of the Mt. Lyell Salamander (H. platycephalus) living in xeric desert-edge canyons on the eastern slope of the Sierra Nevada. In 2018, Bingham et al. partitioned the Shasta Salamander (H. shastae) into 3 species based on mitochondrial DNA, allozyme loci, and modest morphological differences. Those authors acknowledged that the ranges of these northern species were not fully understood, and it was clear that large areas of the Klamath Mountains and other Northern California ranges had not been adequately explored for populations of Hydromantes. In 2022 we began using a combination of satellite imagery and field knowledge to identify several areas that warranted surveys based on geology, elevation, and slope exposure. Over the past several years we have focused survey efforts on increasingly rugged and remote areas in the Shasta-Klamath region. Though surveys are ongoing, preliminary results from our work will be shared along with directions for future research.

Preferred Session: Natural History of Amphibians 

Abstract:

Thigmothermy – the thermoregulatory behavior by which an organism seeks out contact with a warm substrate or object to affect body temperature – is a behavior present in most amphibians with limited access to solar radiation. It is often (correctly) assumed but poorly documented, It typically involves making exaggerated body contact with a warmer than ambient substrate. Thigmothermy has been shown in the Andean Toad (Rhinella spinulosa) during rainfall when its body temperature corresponded to warmer substrate temperatures and not to cooler air temperatures. However, for amphibians, substrate contact may serve a dual purpose: heat absorption by conductivity (thigmothermy) and water absorption through the skin (not thigmothermy). Determination of which is the driving force of the behavior may not always be possible. My observations provide examples of thigmothermy in endangered Arroyo Toads (Anaxyrus californicus). Rather than “casual” thigmothermy – that is, deriving a thermoregulatory benefit by being active and in substrate contact above a critical thermal minimum – my observations evidence the seeking out of warmer-than-ambient substrates by gravid females disproportionately to adult male, non-gravid female, and juvenile Arroyo Toads, which I hypothesize may facilitate egg maturation. Substrates used by some gravid females eliminate the dilemma of purpose.

How do amphibians share stream habitat in their aquatic life stages? The answer is: we have a lot to learn! This study investigates two obligate stream-breeding amphibians whose ranges, breeding seasons, and habitat overlap spatially and temporally in first order streams. We 1) collected data on the aquatic life stages of R. boylii and T. rivularis, 2) applied the existing body of knowledge about R. boylii that is currently based in riverine and higher order stream systems to small first order streams, and 3) compared and contrasted it with habitat use between these two species. We collected data at the meso-, sub-, and microhabitat scale, including canopy closure and fish presence, and looked at spatial distribution throughout aquatic life stages. Key findings highlight the value of runs at the mesohabitat level, low gradient riffles and pocket water runs at the subhabitat level, and patterns in substrate type, water flow rate, and canopy cover among species and life stage. We also identify a novel subhabitat designation that is highly influential to larval life stages: protected side channel pools. Based on these results, we offer specific management recommendations that can support egg and larval development for R. boylii and T. rivularis.

Frequent and more severe fires are affecting wildlife across the Western United States, including higher elevation species such as the Yosemite toad (Anaxyrus canorus). While there have been studies on the effects of fire on western toads (Anaxyrus boreas), the impacts of fire on Yosemite toads are largely unknown. Fires can alter the hydrology of breeding habitat, destroy the upland forests needed for foraging, and reduce overwintering burrowing habitat by decimating rodent populations. Over the past 30 years, fires have significantly impacted Yosemite toad habitats in Yosemite National Park, transforming large portions of the landscape. This presentation will explore the role of fire in Yosemite toad habitats and examine its effects on both historical and current populations.