Which is a true difference between rats and mice?

The statement regarding outdoor food sources in relation to rats is accurate because rats are opportunistic feeders and tend to seek food in a variety of environments, including outdoor areas. This adaptability allows them to thrive in both urban and rural settings, searching for accessible food sources such as garbage and crops. Their behavior often leads them to establish nests near food supplies, which reinforces their reliance on outdoor sources as a critical part of their survival.

While the other options contain some truths, they do not capture as distinct a behavioral or biological difference as the use of outdoor food sources does. For instance, mice do have certain hydration needs, but they can derive moisture from their food and may not require a constant daily water source. Additionally, while rat populations can grow quickly, various factors influence population dynamics, making it less straightforward to assess their overall growth rate compared to mice. Lastly, while mice may exhibit caution toward new objects, this behavior can also be observed in rats. Thus, the behavior concerning outdoor food sources distinctly characterizes rats as opportunistic feeders, demonstrating a clear and relevant difference between the two species.