At the Royal Zoological Gardens “Blijdorp” at Rotterdam May 6th 1958 a Father David’s Deer gave birth to a female calf. It was the first young of this three year old doe. During the days before the day of birth the doe was seen several times leaping upon the buck. Experience with other Ungulates has taught that such behaviour may be regarded as an indication that the time of delivery is approaching. On the day of birth the doe refused her food as has been observed in many other mammals. She lay down very often, gnashed her molar teeth and made movements with her head towards the belly and the udder, the ears flattened to the neck, as if she was suffering from cramps. One had the impression, however, that the expulsion of the young was kept back until the keeper went home and the door of the stable was closed. Apparently a great number of mammals prefer to give birth to their young in the quietest part of the space of 24 hours. For most mammals this is the evening or the night, but bats very frequently give birth during the day which is their time of rest (SLIJPER, 1959). A postponement of birth until all is quiet has frequently been observed in zoological gardens. In natural surroundings the Ringed Seal (Phoca hispida Schreb.) and other Seals are said to be able to postpone birth as long as 10 days if the weather is very bad (KRUMBIEGEL, 1947).