Michael Lynch writes to me:
The prices tell the story. A baby chimpanzee can go for as much as $50,000 (£31,195) or $60,000 (£37434). An adult chimpanzee has no market value. Abandoned adult animals end up in sanctuaries. But in one of the paradoxes of the exotics world, some of the sanctuaries that rescue animals also breed animals to defray their expenses – thereby, arguably, making the problem of surplus adults even worse.
The related story is here.