Experience has taught keepers that introducing pairs of clouded leopards at a young age gives opportunities for the pair to bond and breed successfully.

This means that ground hornbills can normally breed successfully only every third year.

However, some behavior may need to be learned before the birds can breed successfully.

The hybrid offspring were fertile and able to breed successfully with each other, indicating that the two species of bear are closely related.

However, failed breeders that did not help are more likely to breed successfully in subsequent years, so there may be a cost of helping.