I8 CANIDS AND FELIDS I N CAPTIVITY

was pregnant was that she refused to allow the male to mate with her after 19 September 1965. During the final stages of pregnancy the skin of the female’s belly appeared tightly stretched and very smooth. The belly was marked with stripes of faint yellowish-brown, which disappeared a month after the birth, Three or four days before birth occurred, the nipples were slightly erected but they were not very conspicuous.

The gestation period was 68 days, calculated from the last observed mating on 19 September 1965 until the date of birth on 26 November 1965.

The five cubs were dark brown at birth and their eyes, which were closed, opened on 4 December 1965, eight days after birth.

The young were born in a burrow dug by the parents inside the enclosure. The mother kept the young inside the burrow most of the time until they were two months old, though they would occasionally come out at night, either with the mother or alone. During the third month the pups started licking pieces of mutton placed inside the enclosure for the mother, but they continued to be suckled. When they were four months old they were completely weaned and fed on minced meat and pieces of meat.

The male did not take any part in rearing the pups: his attitude seemed to be one of indifference.

mixed exhibit for Polar bears and Arctic foxes Thalarctos maritimus and Alopex lagopus

at Omaha Zoo W A R R E N D. T H O M A S Director, Henry Doorly Zoo, Omaha Zoological Society, Omaha, Nebraska, U S A

The Omaha Zoological Society has recently embarked upon building a large new zoo. As part of the new development a spacious, moated enclosure for Polar bears Thalarctos maritimus has been constructed. The enclosure is built into a hillside which means that the back of the enclosure, cut out of the hill, is more than 6 m high. It is made of reinforced concrete and is covered with naturalistic gunite. The floor of the enclosure is terraced with step-like slabs of concrete, upon which have been stacked a number of very large

CANIDS AND F E L l D S I N C A P T I V I T Y 19

natural rocks. In the centre of the enclosure there is a large pool, 1.2 m deep, and fed by two waterfalls which constantly supply fresh water to the pool. The whole enclosure is 29 m long, 12 m wide at the centre, and tapers to 9 m wide at either end. At the back of the enclosure there is a den for the Polar bears built into the rocks. The animals are separated from the public by a dry moat, measuring 3.6 m across and 3 m deep. There is a hidden ramp at the bottom of the moat so that if any animal should fall into the moat, it can return easily to the enclosure. The ramp also means that the keepers can clean the moat without difficulty.

When the exhibit wasnearly completed, it was decided that we would try to include Arctic foxes Alopex lugopus with the Polar bears. Since the Polar bears would be young animals, it was felt that they would probably adjust easily to living with the foxes and would also be insufficiently agile at that stage to catch or injure them. By the time they were adult we hoped that they would be so accustomed to the foxes that they would not molest them.

Four five-month-old Polar bears (two males and two females) were put into the enclosure, together with three adult Arctic foxes. The arrangement worked so well that we added five more foxes and an additional female bear of about the same age two months later. At first she was not accepted by the other bears, but after six months she had become part of the group.

At the time of writing (June 1967) the bears and foxes have lived together 14 months. The foxes have dens behind the rocks, at the back of the enclosure out of reach of the bears, and this is where they usually sleep. The foxes have adjusted well to living with the bears and do not seem at all nervous. The foxes play together and they have mated. At first the Polar bears chased the foxes whenever they emerged from the rocks, but now their attempts to catch them are very half-hearted. Their main preoccupa- tion is trying to reach the foxes’ food which is placed at the back of the enclosure between the rocks, and out of reach of the bears. Frequently a bear will lean over from the top of a rock, almost standing on its head attempting to reach the food; whereupon one of the foxes makes a determined attack on the bear’s unprotected rear. By the time the bear has recovered and turned round, the fox has retreated to a safe distance from where it contin- ues to threaten the Polar bear. The foxes are most active in the morning and evening. Since the animals have been together there has been only one fatality-when one of the foxes slept on top of the rocks (instead of between them). Unfortunately, the bears woke that morn- ing before the fox did.

We are very pleased with the exhibit and the experiment has proved a fascinating study in animal behaviour.

A similar experiment of exhibiting Grizzly bears Ursus arctos horribilis and Red foxes Vulpesvulpes together had to be abandoned as the Red foxes would not stay out of the moat. The Arctic foxes have never once tried to escape or to climb into the moat.