Final answer:
Birds using a sun compass to orient during migration represents an ultimate explanation, relating to the evolutionary benefits of such behavior. Proximate explanations, in contrast, would consider the immediate physiological mechanisms involved in sun compass navigation.
Step-by-step explanation:
The observation that birds use a sun compass to orient as they fly south in the fall is an example of an ultimate explanation in biology. Ultimate explanations concern the evolutionary significance and history of a behavior. In this case, migrating birds have evolved the ability to use the sun's position to navigate efficiently over long distances, which is a beneficial adaptation for successful migration and survival. This contrasts with proximate explanations, which would focus on the immediate causes of the behavior, such as the neurological and sensory mechanisms allowing the birds to detect and respond to the sun's position.
To further clarify, the phrase 'as the crow flies' is often used to describe the most direct route between two points, which is relevant to how birds generally navigate. Using compasses, whether natural like a bird's sun compass or a man-made magnetic compass, involves orienting along a north-south axis to find direction. Compass needles align with the Earth's magnetic field, providing reliable orientation which some animals are also capable of detecting.