A species can be common in a person’s childhood and rare within the same lifetime.

Something abundant in your childhood can become scarce inside one lifetime. That speed is hard to feel, because the baseline moves with you: each generation takes what it found as normal, and the decline registers only in the memory of people who saw the earlier version. The loss is real and mostly invisible to those born after it.

This is a reason to trust the accounts of people older than you about what used to be here. It is also a reason to notice what is ordinary around you now and record it. What seems too common to be worth mentioning is exactly what nobody will be able to describe later.