[cetalingua]

>When you see it in nature, like in birds and whales, it's about finding a mate.

Not exactly, at least for whales. The humpback whale song's function has not been fully understood. The initial hypothesis that it is a vocal display for females has not been supported, since females do not approach singing whales, and whales sing all over the place, not just at the breeding grounds. So the function of a humpback song might not be solely to find a mate, or might not be related to reproduction at all.

https://www.the-scientist.com/features/the-mystery-of-whale-...

Furthermore, you do need a complex communication system for complex social groups. For example, there are two bottlenose dolphin ecotypes:coastal and offshore. Coastal ecotype is a small fission-fusion society and we see a somewhat simple vocal repertoire. The offshore ecotype lives in big groups and they have very complex vocal repertoire. The bottom line is, at least for cetaceans, we still do not have enough data and understanding to realy argue about the complexity of their communication system one way or another. But it definitely goes beyond of just being "about finding a mate"