three hours, the water became quite clear and after six hours was considered ‘polished water’.

When the aninials were introduced, we began to have difficulties in water clarity. Within two weeks we could not see 3 It. into the pool. Thcre were four dolphins in the pool, each contributing about 9 lb. of waste per day. We tried many types of filter mediums and some chemical admixtures, but we never seemed to make much progress. We called in several water ‘specialists’ and had many analyses made of the water, but still could not nail down the difficulty. After several months of frustrating investigations, Mr Henry Arm- brust of B.I.F. Industries, Inc., Providence, %ode Island, suppliers of the filters, came up with a chemical flocking system that would not injure the animals. This is working well today and we believe Brookfield has the clearest water of any dolphin tank in the country. Moreover, the system is perpetual in operation and it is possible to operate with only adding water for evaporation and spillage.

When analysing the project after a year’s operation, we have come up with certain conclusions. Many of us feel that the project should have been some- what larger. It is extremely popular and more seating could be easily filled. During the summer months, the zoo has four to five packed performances a day. In the winter months, there are two to three a day. Even on the worst days of the past winter, people have ventured out to the zoo to see the show.

A second point to consider is that we have no retention tank in the present filtration cycle. We feel now that we could use a 33 per cent retention period in the filtration cycle and valved so that it can be placed either before or after the filtration stage. We are now workmg on an exhtbit that requires difficult filtration of wastes of unknown characteristics where we are including a re- tention period of 1 0 0 per cent of the turnover cycle. Repritrredfrom Dntnr G. Croaker, April 1962.

A Q U A T I C E X H I B I T S AT W E S T B E R L I N ZOO

by Heinz-Geotg Klos Director, Zoologischer Garten Berlin, Germany

T H E enclosures for pinnipeds at the West Berlin Zoo are among the few animal enclosures that survived the Second World War. They were designed in 1930 by Prof. Ludwig Heck and have always been among our most successful ehbi t s . Rockwork forms one of their most important features; this was con-

structed out of natural rocks from the valley of the river Elbe and selected individually by the architect. They have been arranged in a very natural way. Basically, the e h b i t consists of a large central rock, hidmg the indoor dens and the keepers’ rooms, and four individual enclosures. The Sea lion Pool.This has a maximum length of 87 ft., a maximum width of 43 ft. and an average depth of 5 ft., with a water volume of about 15,000 a f t . The pool is large enough to give the sealions plenty of room to swim and dis- port themselves in. Two species are kept in the enclosure: one male and two female Californian sea lions, Zalophus californianus, and one very large male Antarctic sea lion, Otaria byronia, a species that is characterized by its large bulldog-like mouth. The pool has two dens attached to it and the animals can be shut away in them whde their pool is being cleaned. They are not used as winter quarters since we are able to keep the pool free of ice with a water circulation system. Eight feet above the water-level there is a projecting rock from which the big bull sealions dive at feeding time. The Elephant Seal Pool. This is separated from the seahon enclosure by a broad flight of steps of natural stone, cutting right across the whole enclosure. The stairway is very popular with the public owing to the excellent view it provides of the seal pools and the feeding performances. The elephant seal pool is adapted to the size and t ranqd temperament of its inhabitants. It has a maximum length of 4 ft., maximum width of 32 ft. and average depth of 5 ft.; it holds about 5,000 cu. ft. of water. The edge of the pond is flanked by a flat shore and shallow steps so as to cause the elephant seals as little discomfort as possible getting out of the water. The den attached to the enclosure can be closed by means of three vertical iron bars. We use it occasionally to separate the animals, for instance during mating time. The enclosure houses a pair of Southern elephant seals, Mirounga leonina.

Both the sea lion and the elephant seal enclosures are surrounded by a ditch that has steps on the animals’ side. Thus the animals can re-enter their pool without much Miculty if they fall into the ditch. In the sea lion enclosure, the area between the water and the ditch has a small platform where the animals often lie, just in front of the visitors. The Seal Pool is much smaller than the other pools and has a maximum length of 27 ft., maximum width of 20 ft., and average depth of 3 ft. and holds about 2,250

cu. ft. of water. It contains two flat islands on which the seals lie when it is sunny. There is no ditch in this enclosure and the public are separated from the animals by a wall: the visitor can lean over this and see the seals swimming and diving immediately below him. Inside the rockwork there is a den for the seals. The enclosure contains one male and two female Harbour seals, Phocu uitulina, one of which was born at the West Berlin Zoo.

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All three seal pools are lined with a greenish opaque glass. The animals can be easily seen moving in the water against this light-coloured background. The Penguin Pool has an average area of 500 sq. ft., an average depth of 2 ft. and a water volume of about 950 cu. ft. The pool was not made any bigger so that the water could be changed easily and give the public a good view of these rather small animals. The enclosure is separated from the visitors by a low wall made out of uneven blocks of stone. At the back of the pool there is a sandy shore which turns into a rocky slope. Breeding niches have been built into the rocks and Humboldt’s penguins, Spheniscus humboldti, and Black-footed penguins, Spheniscus demersus, breed there regularly, As well as these species, the enclosure contains Rockhopper penguins, Eudyptes cristatus, four Northern gannets, Sula bassana, two King cormorants, Phalacrocorax bougainuillei, two Great black-backed gulls, Larus marinus, two Herring gulls, Laws argentatus, and four Steamer ducks, Trachyeres brachyprerus. The walls of spacious indoor accommodation can be covered with running water so that even in the summer the temperature does not exceed IS’C. A refrigerated room is available for storing up to two tons of fish at -IOC.

KE E P I N G B E AVE R S, Castor fiber, I N C A P T I V I T Y

by Count Bjom Hamilton Direaor, S h e s Djmpark, Hoor, Sweden

T H E beaver is one of the oldest of all living mammals and it has survived the many changes that the northern hemisphere has been exposed to from the Tertiary era until our time. Past contemporaries of the beaver, such as the mastodon, the mammoth, the cave-bear and many others, have all disappeared. In Sweden the beaver has been extinct since I 870. However, in 1922 a few pairs were imported from Norway and at present the beaver population. in the northern part of the country numbers a few hundreds.

The great Swedish scientist, Linnaeus wrote about the beaver that ‘in the art of building he is surpassed by no living creature except man. With his admirable cleverness he regulates the level of the water outside his house, he digs channels and builds roads for the transport of his necessities from the forest‘.

In 1960 the Skanes Djurpark decided to obtain a pair of beavers. A very suit- able piece of groutid was available with a small stream flowing through it: even during the severest cold, the water is ice-free. With an excavator we enlarged