During the mid 1990s, I worked for over half a year at a zoo on the side of a little mountain in Sudetenland (grazing camels from the Ústí nad Labem Zoological Gardens, pictured left). Eventually, I worked in the zoo's offices, where I maintained an international database on the Hartman Zebra and corresponded with zoos around Europe, China and India about animal exchanges for mating purposes, but for my first four months I was trained to work with all the animals, except for the orangutans and the Asian elephants, as they required special care.
My stories of this time could fill volumes but one concept I took away from the experience was that the minimum structure of each exhibit should consider the maximum amount of containment needed. For example, no bars are required to restrain giraffes; they cannot step down more than a two-foot drop so all you need to enclose them is perhaps a perimeter trench and a small stone wall.
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On a humbler note, below is a picture of the indoor space (for winter and heavy rains) for my kids' guinea pigs. I took it this morning after returning from a run in the hills by my house to fetch them some fresh bamboo. This new setup is only couple of days old as I am rebuilding, repointing and painting my 130-year old basement walls and need to move things around to get to the crumbling areas.
Their "cage" uses a corner of the restored walls and a band of bricks, five high, without mortar. It is easy for me to step into and out of for cleaning and feeding and yet they have no way out as they cannot jump high enough, over or even climb up, such a small barrier. On the right side of the space, you will notice a small sculpture for their contemplation and enjoyment.