RODENTS.

Forest and Bird, Issue 18, 1 August 1929, Page 4

RODENTS.

It is not commonly realised what a wide-spread menace these little animals are. Collectively they make an enormous group, comprised of squirrels, gophers, lemmings, wood-mice, field-mice, rats, and many others. Their chief food is roots or green crops, and they are ultra-prolific. All people are familiar with the procreant multiplication of the common house-mouse, and field rodents are fully as productive.

Their prolificness at times is amazing. During ordinary seasons they merely seem to hold their own in numbers against natural enemies—birds, cats, and small vermin. Even in these days of “peace” their reproduction is great, but not sufficient to attract their enemies in greater force. The presence of fifty or a hundred field-mice on an acre of alfalfa does not affect the crop, and makes merely fair hunting for vermin. Presently, however, a period arrives when the rodents seem to multiply as if by magic. One litter after another is born, and within a few weeks these litters produce new litters. Perhaps birds and vermin have withdrawn from the neighbourhood, attracted to another locality by an abundance of food, and the rodents are free to breed unmolested. Then, without warning, they sweep in countless hoards broadcast over the land.

In this way the lemmings appear every few years in Norway and Sweden. They sweep in incalculable thousands slowly across the country, devouring all vegetation that stands in their path and leaving a brown, barren stretch behind. They pause for nothing, swim broad rivers and lakes, climb mountains, cross prairies, and finally plunge into the ocean. At their first appearance hosts of predatory animals gather. Foxes, wolves, small vermin, and birds of every description assemble on the trail of the lemmings and fight the retreating horde until it is swallowed by the sea. Even cattle and horses trample the rodent army under foot when it attempts to cross their pasture. Nature orders all her living forces to prey upon the insurgents.

The history of Great Britain is filled with mentionings of “plagues of mice” which from time to time have arisen to destroy the meadows and the root-crops. And her history also is replete with reference to the descent of hawks and owls upon the revaging swarms of rodents and the annihilation of them.

The Department of Agriculture at Washington has studied for more than half a century our native raptorial birds (hawks and owls) to determine which species are harmful to the work of man and which are beneficial. The contents of about 50,000 stomachs taken from the seventy-five species and subspecies which occur north of the Mexican line have been analysed.

The results show that out of the seventy-five only six forms are wholly detrimental to the interests of agriculture; beneficial birds form the greater part of their diet.

It is no longer the fashion to call the red-tailed and redshouldered hawks poultry thieves. They are now recognised, like the sparrow-hawk, as birds to be courted, not killed. Poultry make up but 1 per cent, of the food of a red-shouldered hawk and ten for the red-tailed species. The screech-owl, barn-owl, and long and short-eared owls, are given every inducement to remain in the neighbourhood of farms. The American sparrowhawk devours hundreds of insects and field-mice to every songbird it takes. For each bird of economic value consumed, the owls, with the sole exception of the great-horned variety, destroy an average of 400 small rodents two or three are devoured at a meal. Quite different are these records from that of the sharp-shinned hawk, which lives on a diet 98 per cent, bird.

With a multitude of similar facts before us it is no longer possible to condemn the hawk and owl families. All laws should be repealed relating to the killing of these birds, except the incorrigible six, and any other individual caught red-handed in the act of stealing poultry or game. A few States have already put some birds of prey upon the protected list, and the next decade probably will see the entire Union falling in line. The bounty system of paying for the killing of hawks has virtually everywhere been discontinued. The country has thus been saved millions of dollars both in bounties and in crops. The people are no longer willing to pay cash for what really amounts to increased destruction of their own farm products. They have learned through observation, research, and experience that a reduction in the number of raptorial birds is invariably accompanied by a wave of noxious rodents. —The Importance of Bird Life (Innes Hartley).