DISEASE IN BIRDS

Forest and Bird, Issue 58, 1 November 1940, Page 7

DISEASE IN BIRDS

By E. V. Sanderson

A POTENT CONTROLLER

DISEASE is a much more potent factor in checking the overpopulation of an area by any particular species of plant or animal than most people realise. Diseases introduced from outside sources in particular may assume plague-like proportions simply because the need to establish reasonable immunity has not been necessary in the past. Thus a simple malady to the white man like measles may play sad havoc when introduced into a race amongst which it has never been known. The native birds of New Zealand are stated to have suddenly decreased in a wholesale manner before acclimatised foreign predators such as weasles, stoats and rats were established and before the bush was destroyed. The only apparent reason for this is introduced disease. It is suggested by some that the huia, for instance, was attacked by a tick which was imported with this bird’s cousin, the Indian minah. When the possibilities of introducing new grave diseases are considered, one shudders to think of the danger of introducing some of the virulent diseases with which American waterfowl have to contend. Yet mallard are still occasionally being imported from the United States despite the fact that there are large numbers in this country. Presumably the other side of the fence is looked upon as being the better. Also, numbers of various species of birds are constantly being imported for cage enthusiasts, and here again we have a situation comparable to that of children playing with fire. Endemic diseases are one of nature’s methods of preventing any one species dominating an area, and of eliminating individuals lacking the necessary virility to prosper under existing conditions. Foresters in other countries are well aware of the danger of planting large pure stands of timber trees. What is the position when animals are crowded together ? It is only necessary to look at the keeping of poultry in a confined area. Almost anyone can manage a dozen or so fowls, but directly poultry-farming on a large scale is attempted grave troubles

arise. Disease germs in animals are found mostly in a creature’s excreta. When, with a desire to help the birds in their time of need during the winter months, we feed them, and in the summer provide artificial baths, we are causing undue concentrations and unless care and cleanliness are exercised, we may do more harm than good, so far as the birds are concerned. A bird bath, for instance, should have a constant trickle of fresh water entering it, and be cleaned out daily. Sponge cake tins, as used by the late Mr. Robert Nelson on Little Barrier to contain sweetened porridge and milk, are probably the best receptacles for bird food, more especially if placed on a wire platform some height above the ground. The birds feed standing on the edges of the tins and the droppings go below on to the ground. Last summer, for some reason or other, possibly shelter, large numbers of birds, including hundreds of sparrows, decided that the small grounds around my home were a suitable place for a district dormitory. Soon the place began to take on the odour of a fowl yard, but the satisfaction of procuring such a lot of guano without charge made me overlook this. Suddenly the birds deserted for pastures new and clean. Nature demands, as we all know, that man, too, has to contend with disease, but what would the result be if, for instance, the sanitary arrangements of a community broke down or were destroyed by war or if we were unable to bury the dead. War is generally followed by famine and at times plague. Perhaps after all, these dreadful happenings of war are merely Nature’s means of cleansing mankind and reducing his numbers in order that a limited number of his species may survive. With his efficient sanitary arrangements man is able to defy Nature’s restriction of population by disease, at any rate for a time, and to go on his evil ways of destroying the source of his main food supplies—the soil. Nature, however, cannot be defeated. She is well able to look after her own and save man from himself. Her inevitable day of reckoning will come sooner or later. Is it here now ?