Cost-effective are smaller cute day active animals like ring-tailed lemurs, meerkats, otters, prairie dogs and domestics like rabbits, llamas and pygmy goats.
Least cost-effective animals are rarely kept
Small nocturnal mammals (genets, martens, rodents, foxes, bats) have a reputation of being boring to visitors. The same about songbirds and amphibians. Also leaf-eaters like langurs, okapis, duikers are expensive to keep in Europe but not more interesting than their cousins which eat fruit or hay.
In reality, however, it mostly depends on the way of presenting the animal. An African porcupine is boring, but if you have feeding sessions, they become very very popular. Seals and sea lions are generally extremely popular when there are shows or training sessions. But if there are large tanks with underwater viewing and intensive filter, the cost skyrockets and recently some American zoos consider them too expensive to keep.
German zoos used to have a very good knowledge what animals are popular and how to present them to attract the crowds. It goes back to the beginnings of 20. century, when zoos used to be purely self-financing from visitor tickets. The current generation of zoo directors is focused on conservation. However, this entertainment knowledge becomes important again, at the time of financial crisis in the West.
Least cost-effective animals are rarely kept
In reality, however, it mostly depends on the way of presenting the animal. An African porcupine is boring, but if you have feeding sessions, they become very very popular. Seals and sea lions are generally extremely popular when there are shows or training sessions. But if there are large tanks with underwater viewing and intensive filter, the cost skyrockets and recently some American zoos consider them too expensive to keep.
German zoos used to have a very good knowledge what animals are popular and how to present them to attract the crowds. It goes back to the beginnings of 20. century, when zoos used to be purely self-financing from visitor tickets. The current generation of zoo directors is focused on conservation. However, this entertainment knowledge becomes important again, at the time of financial crisis in the West.