Potential effects of highway mortality and habitat fragmentation on a population of painted turtles in Montana /

Abstract

Highways and other road systems can present problems to wildlife populations though direct mortality and indirectly by reducing landscape connectivity by creating significant barriers to movement. These impacts can lead to fragmented populations, alteration of animal behavior, lowered population sizes and, thus, lowered population viability for some species. This research examined the potential effects of human-caused fragmentation on a population of western painted turtles (Chrysemys picta bellii) in northwestern Montana. Two studies were conducted: 1) a Capture-Mark-Recapture (CMR) study to examine survival and movement rates and 2) road mortality surveys to examine the number of road kills and the potential affect on the population. Together these studies help to determine the overall affect of the highway on the population and on the landscape level connectivity of the population. In a 6.4-km (4-mile) stretch of Highway 93 in the Ninepipe/Ronan area, a total of 1,040 turtles were killed from 2002 to 2004. Three priority areas were identified where road mortality levels were very high; the 2 kettle ponds split by the highway and the area near the scenic turnout at Beaverhead Lane. Typically, overwinter survival rates were very high (0.8 - 0.9) and summer survival rates were lower (0.8 – 0.4) when turtles were more likely to be moving and encountering the highway. Annual apparent survival rates were between 0.85 and 0.13 and would not be sustainable in a closed population. These survival rates are confounded with permanent emigration. During the drought, turtles moved off the study site to refugia habitats indicating a larger regional population (i.e., not a closed population), thus, maintaining connectivity across the landscape is essential in order to sustain viable populations in the future. A review of available fencing methods used in herpetofauna-highway interaction projects is provided in Appendix A. An experiment to examine the effectiveness of flashing material as a barricade on low fencing was conducted (Appendix B). Turtles were able to climb fencing material that did not have a flashing barrier. Therefore, incorporating fencing as a barricade or to direct turtles to crossing structures needs to take into account the climbing ability of the turtles. Ultimately, the information in this report can be used to guide design and placement of wildlife crossing structures during the Highway 93 reconstruction project.