Geology topics

Brian D Todd

Publications and source records attributed to Brian D Todd.

5 recordsLinked to original sources

USGS2023

Survival and establishment of captive-reared and translocated giant gartersnakes after release

Many imperiled species face increasing extinction risk that requires interventional management like translocation or captive rearing. The use of translocations to successfully restore or create populations requires that animals survive at recipient sites, information that is often lacking for imperiled species and that can be risky to acquire if not obtained before a species has dwindled in number. The giant gartersnake ( Thamnophis gigas ), a semiaquatic snake endemic to the Central Valley in California, USA, has declined after losing >90% of its historical habitat and may benefit from successful translocations to protected habitat. We released adult and captive-reared juvenile snakes from 2 donor sites into a recently restored wetland in 2019 and 2020 and compared their survival, movement, and activity using radio-telemetry through 2021. We monitored juvenile survival for 2 years in captivity after birth and then estimated post-release survival at the recipient site using radio-telemetry. Just 8% of translocated adult snakes survived >801 days (95% CI = 1–64%) compared with 39% of resident snakes at the donor sites surviving >1,154 days (95% CI = 23–68%). This equated to annualized survival rates of translocated adults ( x̄ = 0.32, 95% CI = 0.12–0.82) that were roughly half that of resident snakes ( x̄ = 0.74, 95% CI = 0.63–0.89). Translocation was negatively correlated with survival, but movement and activity received little support in models. Seventy-six percent of juvenile snakes survived captivity and, once released, juvenile survival was 60% (95% CI = 38–94%) for the 4-month monitoring period before winter. It is unclear why survival of translocated adult snakes was lower than that of resident snakes, but there was little evidence for differences in behavior (e.g., increased surface activity, average distance moved, emigration from the translocation site) that are commonly cited causes of mortality in other translocation studies. Our results suggest that, in the absence of a clear understanding as to what contributes to adult survival after release to a new site, future work using captive-rearing and juvenile translocation may be more promising for establishing and recovering populations than just translocating adults given the high survival of juveniles.

California↗

USGS2020

Brackish tidal marsh management and the ecology of a declining freshwater turtle

Water management practices in tidal marshes of the San Francisco Bay Estuary, California are often aimed at increasing suitable habitat for threatened fish species and sport fishes. However, little is known about how best to manage habitat for other sensitive status species like the semiaquatic freshwater Western Pond Turtle (Actinemys marmorata) that is declining throughout much of its range. Here, we examined the basking activity, abundance, survival, and growth of Western Pond Turtles at two brackish water study sites in Suisun Marsh, California that differed in how they were managed, with one having passive management (i.e., no active water regulation) and another having active management (i.e., water regulated for seasonal hunting). Our results revealed that basking activity was greatest when salinity, water stage, and air temperatures were low, shortwave radiation was high, and wind levels were intermediate. These preferred habitat characteristics often reflected conditions that were naturally maintained at the passively managed, muted tidal site. We also found that turtles were more abundant and had higher survival rates in the passively managed habitat compared to the actively managed habitat (201-323 turtles/km 2 and 96% survival versus 11-135 turtles/km 2 and 77% survival, respectively). Finally, characteristic growth constants from von Bertalanffy models showed that turtles grew more quickly in passively managed habitat compared to the actively managed habitat. Our results suggest that management strategies for this sensitive status species may be more effective if they protect passively managed muted tidal systems that limit or delay extreme cycles of salinity and water levels and conserve elevated terrestrial buffer zones adjacent to muted and full tidal systems.

California↗

USGS2020

Wind, sun, and wildlife: Do wind and solar energy development “short-circuit” conservation in the western United States?

Despite the trade-offs between renewable energy development, land use, humans, and wildlife, wind and solar development continues to transform the southwestern US into a green energy landscape. While renewable energy reduces carbon emissions and reliance on fossil fuels, many studies have emerged on the associated ecological and social impacts of this technology. Here, we review the current state of knowledge on the nexus between wildlife conservation and energy development in the western US since 2010. We revisit pertinent ecological concepts and questions presented in earlier reviews to assess how far the field has progressed in mitigating negative effects. Specifically, we ask, what density or design of development maximizes energy benefits while minimizing negative effects on wildlife, whether the results of previously-deficient before-after control-impact studies are now more readily-available, and ultimately, can the impacts of renewable energy development on wildlife be mitigated? We also provide a case study on the federally-protected Desert Tortoise, a conservation-reliant species in the Desert Southwest US, to highlight efforts to mitigate the negative effects of renewable energy development. Our review concludes that successful mitigation is possible via use of spatial decision support tools, applying novel wildlife deterrence and detection systems developed for existing installed facilities, and incorporating impact studies that provide managers with conservation metrics for evaluating different future development land-use scenarios.

Environmental Research Letters↗

USGS2016

Habitat selection by juvenile Mojave Desert tortoises

Growing pressure to develop public lands for renewable energy production places several protected species at increased risk of habitat loss. One example is the Mojave desert tortoise ( Gopherus agassizii ), a species often at the center of conflicts over public land development. For this species and others on public lands, a better understanding of their habitat needs can help minimize negative impacts and facilitate protection or restoration of habitat. We used radio-telemetry to track 46 neonate and juvenile tortoises in the Eastern Mojave Desert, California, USA, to quantify habitat at tortoise locations and paired random points to assess habitat selection. Tortoise locations near burrows were more likely to be under canopy cover and had greater coverage of perennial plants (especially creosote [ Larrea tridentata ]), more coverage by washes, a greater number of small-mammal burrows, and fewer white bursage ( Ambrosia dumosa ) than random points. Active tortoise locations away from burrows were closer to washes and perennial plants than were random points. Our results can help planners locate juvenile tortoises and avoid impacts to habitat critical for this life stage. Additionally, our results provide targets for habitat protection and restoration and suggest that diverse and abundant small-mammal populations and the availability of creosote bush are vital for juvenile desert tortoises in the Eastern Mojave Desert.

California↗

USGS2016

Ecology and control of an introduced population of Southern Watersnakes ( Nerodia fasciata ) in southern California

Native to the southeastern United States, Southern Watersnakes ( Nerodia fasciata ) are known from two sites in California, but their ecological impacts are poorly understood. We investigated the ecology of Southern Watersnakes in Machado Lake, Harbor City, Los Angeles County, California, including an assessment of control opportunities. We captured 306 watersnakes as a result of aquatic trapping and hand captures. We captured snakes of all sizes (162–1063 mm snout–vent length [SVL], 3.5–873.3 g), demonstrating the existence of a well-established population. The smallest reproductive female was 490 mm SVL and females contained 12–46 postovulatory embryos (mean = 21). Small watersnakes largely consumed introduced Western Mosquitofish ( Gambusia affinis ), while larger snakes specialized on larval and metamorph American Bullfrogs ( Lithobates catesbeianus ) and Green Sunfish ( Lepomis cyanellus ). Overall capture per unit effort (CPUE) in traps declined with time during an intensive 76-d trapping bout, but CPUE trends varied considerably among traplines and it is unlikely that the overall decline in CPUE represented a major decrease in the snake population size. Although we found no direct evidence that Southern Watersnakes are affecting native species in Machado Lake, this population may serve as a source for intentional or unintentional transportation of watersnakes to bodies of water containing imperiled native prey species or potential competitors.

California↗