When the environment fluctuates from one season to the next, the information that’s relevant also changes.[*15] For a North American bird, spring often means sex. The air fills with courtship calls that are absent in other times of year and must now be carefully judged. Fall brings openness: Bare branches make little birds more visible to predators. The ability to localize the sound of approaching danger, which is inextricably linked to fast hearing, becomes paramount. An animal’s Umwelt cannot be static, because an animal’s world isn’t static.
