Final answer:
The outstanding characteristic of river otters is their behavior of building slides along riverbanks, which allows them to play and enter water quickly. They are also known for using tools to hunt and adapt to their aquatic environment with hydrophobic fur and streamlined bodies.
Step-by-step explanation:
When asked about the outstanding characteristic of river otters, it's important to consider several aspects of their behavior and biology. River otters are known for a variety of characteristics, including their playful nature and adaptations for aquatic life. One notable behavior that tends to captivate people is their tendency to build slides along riverbanks, which they use for both play and as a means to quickly enter the water. This behavior showcases not only their playful nature but also their intelligence and ability to interact with their environment in unique ways.
River otters also exhibit a refined hunting technique that includes the use of tools. They are adept at using stones to break open molluscs, which is particularly fascinating because tool use is relatively rare in the animal kingdom, mostly observed in humans and few other species such as chimpanzees and some birds. Furthermore, their hunting is also efficient due to their excellent sight, a characteristic they share with other predators like raptors, but is especially important for an aquatic hunter like the otter.
In terms of their biology, river otters have hydrophobic lipids in their fur, as illustrated in Figure 6.2, which provides them with protection from the elements during their time in the water. This, paired with their stream-lined bodies and webbed feet, are key adaptations for sliding through water with little resistance, adding to the ease with which they navigate their aquatic environments.
In conclusion, while river otters exhibit many remarkable characteristics, the most outstanding would be their behavior of building slides by riverbanks for recreational and practical purposes. Therefore, the correct option for the outstanding characteristic of river otters is building slides (1).