Why we need to incorporate animal behavior into road ecology: A case history with aquatic turtles
To avoid or mitigate the harmful effects of roads and road traffic on animals (habitat degradation, road mortality, barriers to movement), it is essential to understand the behavior of the animals affected by them. This requires answering three general questions: Under what contexts in time and space do animals encounter roads? How do they behave upon encountering the road corridor and when crossing the road surface? What do they do when encountering putative mitigation options such as roadside habitat management, wildlife barriers, or wildlife passage structures? Turtles are demographically sensitive to sources of increased adult mortality, such as road-kill, and there is a growing concern that turtle populations in heavily-roaded landscapes may be declining due to barrier effects of roads and elevated mortality from road traffic. By synthesizing the results of my research on the behavior and population biology of turtles near roads in northeastern New York State, and reviewing the research of others who have studied the interactions of turtles and roads, I will propose answers to each of the three general questions and highlight where further research on the behavioral ecology of turtles and roads is most needed.
Aquatic turtles primarily encounter roads when seeking nesting sites, and many turtles choose to nest alongside roads – roadsides provide warm, sparsely vegetated microhabitat that is similar to other sites selected for nesting. As a consequence, road mortality is skewed toward adult females. Nesting microclimate and soil conditions are radically different from other nesting sites, which likely has important effects on the viability of embryos, though this has received little attention. For terrestrial turtles, both sexes encounter roads when moving among habitat patches, and the barrier effects of roads may be as detrimental as road-kill. Predictive models of the locations and seasonal timing of turtle encounters with roads, developed using road-kill/road-crossing data, movement behavior of tracked animals, and habitat distribution within landscapes, are increasingly being applied to predict where mitigation may be most beneficial in a road network, and to pinpoint where to avoid locating new roads. Controlled behavioral experiments and field trials of barriers (fences and walls) and subterranean passages (culverts) indicate that these technologies can be effective at reducing mortality while maintaining habitat connectivity between the two sides of a road, but that careful post-installation monitoring and adaptive management are essential for the success of mitigation efforts.