In recent years, placing indoor enclosures for elephants, monkeys, apes, hippo's, ... inside some sort of greenhouse with birds has become very popular. To name a few: Rimbula (Emmen), Hippodom (Köln), Pongoland (Leipzig), Africombo (Magdeburg),... Without doubt these enclosures are wonderful for the visitor, and they help using the limited space the most useful. This might sound really weird, but in a certain way this has always puzzled me: how do they keep those birds in. Do they lock the mammals out, so that the gate is only opened for a little while or do they use some sort of system that the mammals can pass through but the birds can not.? I do know one case, in Planckendael, where gibbons could acces their outdoor Island via a hatch covered by a rubber flap. Now for these small hatches I can see how this works, even for small songbirds. With larger mammals like the elephants in Emmen, I however fail to see how such flaps can keep covering the entire gap consistently after an elephant would pass through without leaving a single gap large enough for some small songbirds like bulbuls. In Blijdorp, I know that the outdoor enclosures of the Okapi's are inside an aviary, eliminating the possibility of bird escapes through there. This is however often not an option for an elephant enclosure for example. As stated above, doors that are sealed off most of the time would work, but this would mean that mammals are either put inside or outside instead of having acces to both. Seen as in a lot of northern zoos, there are many days when it's hot enough to give the animals acces to their outside enclosure but too cold to not give them acces to the indoors. In those case, they just let the doors open for the animals to choose. If this system however would mean that open-door is no longer an option, wouldn't that mean that these mammals are forced to spent a lot more time indoors? Maybe someone who has some more inside-knowledge of this can shed some light on this, and off-course feel free to give your opinion about the pros and cons off this system.
The Africa Hall at Dresden Zoo houses free-flying birds with indoor elephants. At the visitor end, chain-mesh barriers aim to prevent birds passing through - though this hasn't stopped a few specimens getting out, nor house sparrows getting in. As for the elephant end; they do not have free access to both indoor and outdoor spaces; egress from the building is managed by keepers, and elephants pass through a short, fairly low and darkened corridor connecting the inner and outer doors, I think (?) with only a plastic curtain (if anything at all) preventing birds getting in/out if they really wanted to. Otherwise both sets of doors remain shut. All amenities for the birds (heavy planting, feeding / perching / nesting sites etc.) are placed well away from exits, further helping to discourage them making a break for it. The combination of physical and behavioural discouragement is by no means perfect, but presumably works well enough, though personally I don't believe how these sorts of houses work are the optimal management solutions, nice though I think the idea is. Better to cleverly net off the public (and free-flying) side from indoor large mammal accommodation and let the big beasties move freely between indoor, outdoor, public and private spaces at will.
