Basically an idea based on the discussion about the issue of cub overpopulation in the game over in the watering hole:The Giving Tree hints at a problem.

The Giving Tree is overflowing with cubs, and I think the problem basically boils down to too much supply, too little demand. Gorilla Enclave on its own is not enough.

My suggestion is adding a new area for donating extra cubs/adolescents (Maybe adult males? But the issue of submales being kinda useless is a separate one tbh) that is focused around the idea of conservation and repopulating into the wild. Basically relocating spare cubs into "a new area" that has a dwindling lion population. This would mostly be RP flavor, but I think it ties in with Lioden's message about conservation and preserving our wildlife. I think it would also make some players feel good, like they're breeding for a good cause.
In return the player gets a small currency reward to spend in a shop tied to the repopulation section.
It could be a static shop or potentially, depending on how much of a work increase it would be, a rotating reward pool (different set every month, randomized every week, whatever isn't too cumbersome for devs).

Edit for Clarification: Shop is just a suggestion, not a necessity. Even just a minor reward in return for a cub (similar to FR's Exalt option as Ricky pointed out below) would work.

Possibly with a daily cap on the amount of cubs you can donate, so that it doesn't replace the giving tree/selling/chasing entirely. Just adds one more avenue of Demand.
Another potential aspect could be to scale the reward based on age/training %. Basically give us a reason to invest in our young even if we're not keeping them around.

I think it would benefit trade too, as players can sell the shop rewards to those who aren't interested in developing their spare cubs. In summary, I think we just got too many cubs and don't have anything to do with them. Even if its just "hand over 5 cubs and I give you 1 nesting material" levels of basic, I think it would be better than just letting several thousand cubs rot in the Tree.