A robotics-oriented taxonomy of how ethologists characterize the traversability of animal environments

Abstract This article surveys 21 studies of how ethologists characterize the environment for arthropods, reptiles, mammals, and birds traversing above ground, below ground, and burrowing in order to provide insights in selecting or designing a robot for a complex work envelope, for example, the 2018 Thailand Cave rescue. Roboticists are currently forced to rely on empirical expertise to select or design robots and to construct ad hoc testbeds for expected environments due to the lack of comprehensive quantitative metrics. Fortunately, ethologists have been grappling with how to quantify environmental factors that impact the traversability of different animals. That community has collectively identified 21 characteristics which this article discusses and groups into a novel taxonomy of three broad categories: local navigational constraints, surface properties, and global layout properties. One conclusion is that the set of appropriate characteristics for a specific environment depends on the scale of the environment to the agent. The article also makes four recommendations to aid roboticists in a) selecting a particular robot suitable for the environmental characteristics, b) building testbeds that are more representative of the target environment or to objectively compare different robotics, and c) collecting data about an environment for use cases or work analyses. It also discusses the limitations of the ethological studies for robotics and the remaining gaps.