Overview and Background: 

For many pond-breeding species like the Spotted Salamander (Ambystoma maculatum), they rely on mass migration events once a year to facilitate breeding. This large migration usually spans over a couple of months out of the year, depending on where you are. Many scientists have tried to correlate the timing and magnitude of migratory movements with a series of covariates; however, success has varied. Spotted Salamanders may travel up to a quarter of a mile to pond breeding sites–many of which are accessed via road crossing. Having the ability to predict when these mass migrations will be is critical given that road mortality proves to be one of the largest threats to pond breeding species.  This study assesses the role of citizen science in compliment with a case study evaluating how volunteer intensity, frequency, and distribution influence minimum population size, population growth rate, and years to extinction of the Spotted Salamander. 

Methods: 

To evaluate how volunteer participation in amphibian “road rescue” citizen science programs affects Spotted Salamander conservation, the authors used a stochastic population simulation model. Rescue efforts were all in an effort to help amphibians safely cross the road during their annual breeding migration. For example, volunteers might patrol certain segments of the road near breeding ponds, picking up salamanders and carrying them across the road. They modeled a single Spotted Salamander population in the northeastern U.S over 50 years, incorporating demographic structure, breeding probabilities, road mortality probabilities, and forest and pond survival rates.  In addition, they created over 360 unique volunteer strategies, including parameters such as intensity, frequency, and distribution.  The figure below illustrates the Spotted Salamander annual migration cycle between forest habitat and breeding ponds with a yellow line representing a road. The different buckets represent when volunteers can intervene (1) adult in-migration to ponds in early spring, (2) adult out-migration after breeding, and (3) metamorph out-migration from ponds to forest in midsummer. 

Results: 

Almost all volunteer strategies improved conservation outcomes compared to the baseline of doing nothing. Populations with rescue events had larger minimum population sizes, higher growth rates, and longer times to extinction while focusing on juvenile migrations yielded the greatest improvement. They determined that the optimal strategy entailed 10 volunteers per night during all migratory nights. That being said, lower volunteer numbers still achieved higher results than doing nothing. 

Reflections and Critiques:

 Understanding how to navigate pond-breeding species that rely on a couple months out of the year to survive and reproduce is complicated, especially in urban areas where developments are encroaching upon these ponds. Overall, metamorphs (juveniles) have the largest payoff for long-term conservation given these are such long-lived species and timing matters. You can have as many volunteers as possible out at once, but if you do not understand when the conditions are right, you may not be benefiting many of these amphibian species. After reading this paper, I find it obvious that steps need to be taken to understand the environmental variables that correlate with these migratory events to perfect the timing of efforts being made. I know papers have been written doing so, but it is extremely difficult given that these events vary year to year. Depending on the amount of rainfall, the consistency of the rainfall, and the temperatures, migratory events might be delayed or even come early. These events take months of organization and planning to ensure volunteers are available and understand what they are doing. It is difficult to plan around something that is highly variable. That being said, some help is better than no help, but it is far more complicated than training a group of people to scoop up some salamanders in the rain. 

Reference: Sterrett, S. C., Katz, R. A., Fields, W. R., & Grant, E. H. C. (2019). The contribution of road-based citizen science to the conservation of pond-breeding amphibians. Journal of Applied Ecology, 56(4), 988–995. https://doi.org/10.1111/1365-2664.13330

Background and Purpose: With an exponentially growing populations comes infrastructure, accompanied by roads. The direct and indirect effects of roads have been and will continue to be an important conservation concern for species that utilize a network of connected habitats. Most all taxa are affected by roads, however, herpetofauna, especially freshwater turtle species are disproportionately affected by additive adult mortality.  Being an already vulnerable species group with high juvenile mortality and high adult and subadult survivorship, anthropomorphic stressors, such as road mortality, are concerning. Roads not only act as a barrier of dispersal—effecting gene flow and changing animal behavior, but they are also the leading causes of death for some species. For turtle species, roads disproportionally effect nesting females who travel large distances across a landscape gradient—leading to a shift in sex ratios. Species like the Spotted Turtle who use a combination of wetlands and upland habitat across the landscape are more at jeopardy than wetland species that facilitate life processes in a single wetland. 

Study Species: Spotted Turtles are a small, freshwater wetland species that inhabit a variety of wetland types including vernal pools, bogs, marshes, roadside ditches, and small streams. With an expansive range from southern Canada to northern Florida, Spotted Turtles are found in many environments across the Atlantic Coast. They are declining across their range, however, due to a variety of environmental stressors including poaching, habitat fragmentation, wetland loss, road mortality, pollution, illegal trade, and many more. Spotted Turtles have a short active season, being in the water from March through June, and then aestivating and nesting during the summer months. They have large home ranges, especially nesting females—using the upland habitat bordering their wetlands as areas for nesting, short migration between wetlands, and aestivating. With an increase in urbanization, these upland habitats are being highly fragmented by roads—leading to high rates of road mortality. Although there is much said in the literature about the impacts of roads on turtles, there have been few examining the impact of road mortality on freshwater turtle populations. 

Methods and Results:  The study site was located in central Maryland with a paved, two-lane road intersecting it. The average number of vehicles driving on the road was 2017 to 2087 vehicles per days. North of the road were four ephemeral wetlands totaling 6.94 hectares in area. To the south were three permanent and one ephemeral wetland. Spotted Turtles were caught by hand and collapsible mesh minnow traps. All turtles were marked and measured. Both sides of the road (including the northern and southern wetland complexes) were treated as separate populations. PVA’s or population viability analyses were used to simulate Spotted Turtle population trajectories under baseline conditions with added road mortality.  

After running the models, both the northern and southern populations showed negative growth rates. Without road mortality, extinction risk is about 20-24% in 150 years, however, with road mortality, extinction risk is greater than 90%. Every slight increase in adult mortality increases the rate of extinction. While road mortality itself was only around a 2% loss annually, it is catastrophic for these small, isolated Spotted Turtle populations. 

Importance: There are large data gaps into what we know about Spotted Turtles, specifically in more robust populations where they are more abundant. This study is one of the first studies to attempt to quantify the direct effects that roads have on freshwater turtle viability. Although Spotted Turtles suffer from a variety of environmental stressors as mentioned before, road mortality can dramatically reduce population viability.  Many of the isolated areas Spotted Turtles inhabit are now being affected by urban sprawl and increasing infrastructure. These once remote upland area are now surrounded by neighborhoods, and many of these wetland complexes have been segmented by roads. There have been other studies looking at road mortality on freshwater turtle populations but depending on the species and the current status and structure of their populations, even large starting populations may have high extinction probabilities. 

Future Work: In North Carolina, road mortality appears to be especially high in areas like the inner/outer banks where Spotted Turtle populations are more robust. In my research, I have noticed that rural areas with multiple wetland complexes seem to result in high road mortality rates in Spotted Turtles. Although these areas are not city centers, and you may not even consider them urban, the infrastructure necessary to support growing populations is there. Studies like these should be replicated across Spotted Turtles’ range. Given that these turtles inhabit such a broad variety of ecosystems, the replication of this study in more southern populations is pivotal. Slight differences in behavior across populations may yield different results related to road mortality. In North Carolina, our populations are more active during the Spring months, and towards the end of May females will begin traveling to nest. For some wetland species, like the Spotted Salamander, that make great migrations once a year to reproduce, people have collaborated with local departments of transportation to aid in these mass movements during the winter months. Although it may not be as realistic for Spotted Turtles, there are ways to mitigate road mortality. Because Spotted Turtles are considered a species of concern in some places across the United States and are listed as endangered through the IUCN, you would have to be careful not to reveal the exact locations of these populations due to poaching. Progress is currently being made to increase the detection of Spotted Turtles across their range through a Competitive State Wildlife Grant funded by USFWS. By increasing the amount of data we have on Spotted Turtles in general, we can make informed conservation decisions regarding road mortality and other stressors threatening their status. 

Reference: Howell, H. J., & Seigel, R. A. (2019). The effects of road mortality on small, isolated turtle populations. Journal of Herpetology, 53(1), 39–46. https://doi.org/10.1670/18-022