@Mr Gharial The barrel in the foto looks like they're at least aiming for breeding. But if breeding hasn't worked out yet, they probably don't have any experience of how compatible it is with visitors.
@Cyathea I wouldn't say they don't have experience. Diergaarde Blijdorp / Rotterdam zoo is well over 100 years old, the Rivièra hall being built in the 1940's. Although I obviously can't say exactly how long they've had Wreathed hornbills free-roaming here, they've had them for at least 30 years
@Mr Gharial Thanks for the insights. But I did mean experience about the compatibility of breeding hornbills with visitors. Especially here where it at least looks like the breeding cavity is not far away to the path, I wonder if breeding hornbills would defend this area against visitors or not.