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Brazilian tapirs Tapirus terrestris. As the old pair did not breed, a second female Black rhino was bought. Other animals living in the new house are a pair of young Southern White rhinoceroses Diceros s. simus, three hippopotamuses Hippo- potamus amphibius, and the shoebill.

Perhaps for the first time in a zoo an esperi- ment was made of keeping Cattle egrets Bubulcus ibis together with the rhinos and hippos inside the house. About 20 of these small white egrets fly completely free in the house. During the first few weeks they did not even dare to sit on the backs of the rhinos, as they do in the wild. However, they soon grew accustomed to them and visitors to the Zurich Zoo can now enjoy the fascinating sight of egrets riding on the backs of rhinos. The

birds do not try and get out of the house as the exit used by the public has double doors, and the animals’ esit is a dark passage.

Since the Africa House was opened it has worked extremely well and several animals have already bred successfully: some of the Cattle egrets have hatched young and for the first time in Switzerland a River hippopotamus has been born.

R E F E R E N C E S HEDIGER, H. (1956): Tiergartenbiologie und ver- gleichende Verhaltensforschung. 2. Siugetierkde., ZI : 1-28. H E D I G E R , H. (1965): Mensch und Tier in Zoo: Tiergartenbiologie. Riischlikon-Zurich : Albert Miiller.

Hippopotamus house at Melbourne Zoo J. H. S U L L I V A N Director, Melbourne Zoo, Australia

On 15 May 1966 Melbourne Zoo opened its new hippopotamus enclosure. Before the opening and for several weeks afterwards a number of problems were encountered and the way in which each of these was dealt with is recounted below.

Design and construction of the new enclosure were undertaken by a well-known firm of Mel- bourne architects, Messrs Garnet Alsop and Partners. It is designed to house two adult and one five-year-old hippopotamuses Hippopotamus amphibius. There are three units, each separated from the other, so that different age or family groups can be segregated as necessary. The exhibit simulates a meandering African river: an apparently continuous river is divided by simple rock walls into three pools, each about 60 m long round the external perimeter. The animals enter the water from a gently graded ramp and continue into the pools where the maximum depth is about 1-5 m. At this depth the animals can either swim or lie on the bottom of the pool. The deep parts of the three pools are placed alongside the public viewing gallery for two reasons: to provide a physical barrier to prevent the animal from escaping and to ensure that most of the time the hippos are within a few feet of the public. On the far side of the water there are level areas of dry

land where the animals can rest in view of the public. In addition, in each enclosure a small peninsula of dry land extends into the pool area.

One of the pools has been designed as a breeding enclosure : all gradients are specially gentle and edges are curved so that the young hippos will not be hurt.

Each enclosure is surrounded by rock walls with large flower boxes on top so that eventually vines and exotic plants will provide a tropical background for the animals. The flower boxes and other garden areas in the exhibit have built-in water sprays, operated by remote control.

The pools are emptied and refilled every second day. A ca. 5-cm suction pump, installed in a service area out of sight of the public, empties the pools through a ca. ~o-cm pipe that discharges vin settling pits into the main sewer. A larger pump would probably be more efficient but none is available in Australia. The pools are filled from a 7-cm water service by pressing a switch that opens a solenoid valve. When the pool is full the water touches an electric probe and this shuts off the solenoid valve. In case an electrical fault should occur in the solenoid, there is an overflow outlet, slightly above the desired water level.

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Behind the pools, out of sight of the public, are three draught-free sleeping dens constructed from brick and concrete. The hippos are fed in the dens. They have interconnecting doors so that the animals can easily be moved from one to the other. The doors are operated by remote control outside the dens.

The public sees the animals from a shaded gallery running round the pools: as viewing is from a darkened area, this has the effect of high- lighting the animals. As the pools are so deep, no metal bars are necessary to separate the animals from the public. Instead they are divided by white-painted wire screens. The design of the public gallery has intentionally been kept sombre and heavy in order to try and capture an impression of the ponderous hippo. However, it will not be until the flowers on either side of the viewing gallery are full-grown that the tropical effect will be completely realised.

The old hippo pools containing the adult pair of hippos were 45 m away from the new en- closure and between them was a lake and a picnic lawn. We considered two methods of transferring the animals: either by means of a long corral, or in specially constructed cages. We rejected the first on grounds of expense and risk to both the animals and staff if the corral was not sufficiently strong. Instead, we constructed two identical cages, each measuring GU. 1-3 x 3-9 x 1.8 m high, and each weighing about two tons. The basic principles of design were the securing of zox 6 cm mesh 9-5 mm gauge wire with I ~ X 5 cm channel comers and 7x 7 cm angle iron laterals and dia- gonals. Heavy vertical slide doors were provided at each end, operated by a simple rope and pulley arrangement. The floor was made of thick timber and the sides, roof and doors were lined with 3.1 mm steel, welded to the outside. The steel was to prevent abrasion to the animals, to keep the cages fairly dark, and to enable the cages to be used in the future for shifting animals such as bears or apes.

The cages were placed I m inside one of the old enclosures and as the cage floor was 15 cm above ground level, the hippos were required to step up to them. After four days on a light diet neither animal had ventured sufficiently far inside either cage for the doors to be closed. Attempts were made for two hours each morning and even- ing, with some staff holding the door ropes while

others supplied food at intervals along the cage floor, to try to lure the animals further and further inside. At no stage was physical en- couragement contemplated as the animals were far too dangerous to permit familiarity. At the end of the fourth day it was evident that the hippos were being put OK by the upward step. The cages were therefore shifted to the outside pavement which was cu. 15 an below the level of the enclosure, thus making the entrance smoother. The steel lining of the far door was removed to provide more light. On the evening of the fifth day the adult male entered the cage and was successfully restrained in it. His cage was then placed in line with the empty cage (previously they had been side by side) so that the female could see the male. This had no significant effect and was abandoned, Probably the animals were dis- inclined to move very far into such a restricted space; perhaps longer cages might have produced quicker results.

The cage containing the male was lifted by an 8-ton fork lift on to a low-loader trailer and taken to the back of the new enclosure where the hippo was released. The only difficulty following the release was that because of the high water level in the pools, the shape of which was quite different from the old pools, the hippo could not see the point of entry into the water clearly. The level was reduced slightly to overcome this problem,

The cage was next taken to another area where the offspring of the adult pair (five-year-old ‘Henrietta’) was kept. At first she was reluctant but after about an hour was eventually persuaded to enter the box and was transferred comparatively easily.

The same cage was then placed end-to-end with the cage positioned for the adult female. Both inner doors were opened and food placed in the far cage but at the leading end. After two hours of coaxing, when it was almost dark, she entered the cage. She was transferred to the new enclosure the following day.

The temporary separation of the adult pair had little or no effect on them. Each hippo was com- pletely calm from the moment it was caged until it was released. The only injury incurred was a slight abrasion above the female’s right eye. None of the hippos seemed to have any qualms about the new environment and within minutes of being released were all enjoying a swim in the pools.