Turtles in Oregon Face Competition From Non-Native Species

By Ashley D’Antonio

Urban-proximate parks are incredibly valuable destinations for nature-based recreation in landscapes often dominated by human development. These green spaces can also serve as refugia and protect important patches of habitat for wildlife species. Minto-Brown Island Park in Salem, Oregon is both a refuge for residents of Salem who seek opportunities for outdoor recreation and a refuge of habitat for numerous species of turtles. At 1200 acres, Minto-Brown Island Park is the largest park in the state capital of Salem. The park is bordered by the Willamette River and includes 29 miles of multi-use trails that snake through shaded woodlands and past sloughs and ponds. Minto-Brown Island Park also protects critical habitat for two of Oregon’s “Strategy Species” – the western painted turtle and the northwestern pond turtle. Strategy species are native species in Oregon that are of conservation concern due to small or declining populations.

The western painted turtle and northwestern pond turtle are not just sharing Minto-Brown Island Park with outdoor recreationists. One of the reasons the populations of these reptiles are struggling is due to competition with another, invasive turtle species – the red-eared slider. Red-eared sliders often grow larger than native turtles and compete for basking sites. Basking is essential for turtles to regulate their body temperature. Therefore, it’s important that western painted turtles and northwestern pond turtles have opportunities to bask undisturbed.

Various conservation efforts have been made in Minto-Brown Island Park to help the two native freshwater turtle species, including providing artificial basking structures (made of PVC and wood) on ponds and sloughs throughout the park. However, little research to date has examined how outdoor recreation may also affect western painted turtles and northwestern pond turtles basking behavior. In addition, no research to date has shown what the mechanisms of disturbance might be (i.e., Noise level? Speed? Activity type?).

Recreation ecologists, Dr. Ashley D’Antonio, at Oregon State University and herpetologist, Dr. Gareth Hopkins, at Western Oregon University teamed up to conduct a preliminary observational study of outdoor recreation and turtles in Minto-Brown Island Park. Specifically, they investigated if outdoor recreation was a disturbance to turtles and if there were differences in how the three turtle species respond to outdoor recreation. Anecdotal evidence suggested that red-eared sliders are more tolerant of outdoor recreation and seem resilient to disturbance by continuing to utilize basking structures regardless of the amount of nearby outdoor recreationists.

The project team collected over 500 hours of observational data in Minto-Brown Island Park during the summer of 2022. During this preliminary study, they counted and identified turtle species. They also counted the number of visitors that passed by turtle ponds with basking structures, separating the counts by activity type (i.e., biking, dog walking, running, etc.). Across the 500 hours of observation, the researchers counted over 2,100 people and 305 turtles.

Generally, they saw more turtles overall (regardless of species) when there were fewer outdoor recreationists. Overall, the researchers observed 92 instances of outdoor recreationists disturbing turtles (meaning the turtle changed its behavior in an observable way). With over half of those interactions (or 67% of the time), the turtles reacted to being disturbed by stopping their basking behavior and jumping into the water. They also found differences in how the native and non-natives species reacted to outdoor recreation. When both outdoor recreationists and native turtles were present together, 45% of the time (for both native species), they reacted to the presence of people – most often by jumping into the water. Meanwhile, the red-eared sliders only responded to the presence of recreation 12% of the time and, more typically, would just move slightly instead of stop basking altogether. Overall, preliminary results demonstrate that outdoor recreation is an added pressure to native freshwater turtle species in Minto-Brown Island Park on top of the competition with red-eared sliders, a species that seems to be less impacted by recreation use.

Findings so far:

-Turtles tend to be present when there are fewer outdoor recreationists
-All types of recreation tend to negatively predict turtle presence
-Not all types of recreation cause disturbance equally cycling was more likely to cause disturbance than walking
-Disturbance usually completely disrupts basking, forcing turtles to flee, regardless of the recreation type
-Red-eared sliders are significantly less reactive to outdoor recreation, and less likely to stop basking compared to native species.

For the next steps of this work, researchers are using the findings to develop interpretive signage and educational materials for Minto-Brown Island Park visit