NATURAL ENEMIES OF THE RAT.

By David E. Lantz,

Assistant Biologist, United States Department of Agriculture.

INTRODUCTION.

Undoubtedly the great increase of rodent pests throughout North America is in large part due to a general scarcity of the animals that habitually prey upon them. Since the early settlement of the country persistent warfare has been made on birds and mammals of prey on the plea that they are enemies of poultry, game, and insectivorous birds. Efforts to destroy the predaceous birds and mammals have been greatly stimulated by the payment of municipal, county, and state bounties, and the destruction has gone on until in many sections these animals have nearly disappeared.

The effect of killing off the natural enemies of rodents has been to disturb natural conditions. Rodents multiply so rapidly that they derive an undue advantage in the struggle for existence when their natural enemies are destroyed. The result is noticeable in the increased depredations of rats, field mice, rabbits, and other pests.

The destruction of carnivorous wild mammals and birds by the farmer, hunter, or game preserver is often due to misapprehension. Because one kind of hawk preys on the farmer’s poultry is not sufficient reason for exterminating all hawks. Nor does the fact that occasionally an owl or a skunk destroys a chicken or a game bird justify warfare on all owls and skunks. It is the occasional individual and not the species that offends.

ANIMALS THAT DESTROY RATS.

The usefulness of the natural enemies of the rat must not be overlooked in plans for its repression. Among the more important are the larger hawks and owls, skunks, foxes, coyotes, weasels, minks, and a few other wild mammals; as well as cats, dogs, and ferrets among domestic animals, and snakes and alligators among reptiles.

HAWKS.

Most of the larger hawks destroy rats. Feeding only in the daytime, they seldom find their quarry near houses and barns, where rats do not venture out until after sunset. Besides, owing to persecution 164by farmers, hawks generally keep away from farm buildings. In the open fields, however, where rats feed in early morning and late afternoon, hawks find many of the rodents.

The species of hawks that more commonly feed on rats are the buzzard hawks, including the red-tailed (Buteo borealis and sub-species), the red-shouldered (B. lineatus), the broad-winged (B. platypterus), and the Swainson (B. swainsoni); the rough-legged hawks (Archibuteo), two species; and, to a less extent, the marsh harrier (Circus hudsonius), and a few other species.

The writer has several times found the remains of rats about the nest of the red-tailed hawk. Of the 562 stomachs of this species examined by Dr. A. K. Fisher, of the Biological Survey, less than 10 per cent contained poultry or game, while more than 70 per cent contained injurious rodents.^[AH] Most of the other species of buzzard hawks made a better showing even than this, especially the Swainson hawk, which had fed entirely on harmful rodents and insects. The stomachs of rough-legged hawks examined nearly all contained harmful rodents and none of them contained remains of birds of any sort.

A few months ago, while walking on the Potomac flats near Washington, the writer met some boys who had just shot a red-tailed hawk. Its crop was greatly distended, and later examination showed that the bird had recently eaten an enormous brown rat. Although the shooting was contrary to law, when it was reported to the nearest policeman, his comment was, “Oh, a hawk! Why, it’s a good thing to shoot a hawk.” The incident illustrates the general popular prejudice against all hawks.

OWLS.

Because they hunt by twilight and at night, owls are more efficient than hawks in destroying rats. All American owls, except the more diminutive species, prey on the common rat. Even the little screech owl (Otus asio) feeds on young rats.

Of all our species, the barn owl (Aluco pratincola) is preeminent as a destroyer of rats. It lives commonly about farm buildings, sometimes even making its nest and rearing its young in the pigeon loft without molesting the pigeons. In such surroundings its opportunities for securing rats are excellent, and no other wild bird is so useful on the farm. The late Henry Newman once stated that every barn owl is worth £5 a year to the British nation, and the value of the bird to the American farmer is not less.

Owls, hawks, and other birds of prey that swallow their quarry whole or in large pieces do not digest the bones, fur, and feathers. They eject these indigestible parts in the form of large pellets, in which the fur or feathers surround the bones. The contents of these casts 165are an excellent index of the food of owls. Dr. A. K. Fisher, of the Biological Survey, has examined 987 pellets of a pair of barn owls that live in a tower of the Smithsonian building in Washington, and in them found the skulls of no fewer than 192 rats (Mus norvegicus), together with those of 554 common mice and 1,508 field mice (Microtus pennsylvanicus).

Dr. John I. Northrop found a nest of the barn owl on Andros Island, Bahamas. It contained two young owls and the remains of a black rat (Mus rattus). The ground about the nest was covered with pellets which contained remains of the black rat and no other species.^[AI]

The great horned owl (Bubo virginianus) is the largest of our resident owls. It feeds mainly on rodents, though occasionally it takes a fowl found roosting in an exposed situation, as on a fence or in a tree. While it occasionally destroys game birds, the rats it captures would probably destroy ten times as much game as the owl. Charles Dury, of Ohio, in 1886 published a letter from O. E. Niles in which it was stated that he counted 113 dead rats at one time under a nest of this bird.^[AJ]

The snowy owl (Nyctea nyctea) is a rather rare winter visitor in the northern United States. It usually arrives when the ground is covered with snow and ordinary food is scarce. Near barns, outbuildings, and stacks it finds its chief subsistence in the common rat; and, if undisturbed, will stay for several weeks in the same locality, destroying many of the pests. Unfortunately, mounted specimens of this beautiful owl are so much in demand that the majority of them fall a prey to the specimen hunter and the taxidermist. The destruction of this bird should be prohibited under heavy penalties.

The barred owl (Strix varia), the long-eared owl (Asio wilsonianus), and the short-eared owl (Asio flammeus) all destroy some rats; but as they do not generally nest or live in the vicinity of farm buildings, the rodents they capture are taken chiefly from the fields. Occasionally a short-eared or a long-eared owl makes its winter home in a group of evergreens near the farm buildings, and does excellent service in clearing the premises of rats and mice. Evergreens are desirable about a country place, if for no other reason than that they attract owls.

The practice of indiscriminately destroying hawks and owls should be discouraged. Game preservers especially should realize that the birds of prey they kill would, if allowed to live, destroy rats, which in the course of a year do many times as much harm to game as the supposed offenders do. Besides, the birds would destroy also large numbers of mice and injurious insects.

166The farmer and the poultry grower may easily learn to recognize the few harmful species of hawks, and should confine their warfare to these. The practice of setting pole traps for hawks and owls is exceedingly reprehensible, as it results chiefly in the destruction of our beneficial owls when they come about the premises at night in search of rats. Furthermore, the beneficial hawks and owls should have legal protection. The larger hawks, nearly all of which are beneficial, are slow of wing and much more likely to be shot than the swifter and more harmful falcons.

NATIVE WILD MAMMALS.

Not many species of wild carnivorous mammals live where the common rat is abundant. Coyotes, foxes, and a few others occasionally find a rat in the fields, but for the most part they depend for food on native wild rodents and other animals. Chief among the mammals that do good work in destroying rats are skunks, minks, and weasels.

SKUNKS.

Skunks are excellent ratters, and when they take up their abode on the premises of the farmer, they speedily destroy or drive away all rats and mice. This statement applies equally to the large skunks (Mephitis) and the little spotted skunks (Spilogale). Unfortunately, skunks are seldom allowed to tenant the premises without being molested by either dogs or men. When undisturbed, they are inoffensive, and will stay about the farm buildings or stacks until rats and mice are no longer to be had for food.

Skunks usually hunt by night, and hence poultry properly housed is safe from them. The larger skunks do not climb, and can capture only fowls that roost on the ground. Indeed, so few skunks ever learn to kill poultry that there is no good reason for warfare on the skunk family. Besides destroying mice and rats, the animals are invaluable as consumers of noxious insects, especially cutworms, army worms, white grubs, May beetles, grasshoppers, crickets, and sphinx moths.

WEASELS.

Weasels are good ratters and mousers. Several of our species come about buildings, and often perform excellent service in destroying rats and mice. They are more likely than the skunk to attack poultry, for they can enter the poultry house through smaller openings. At times weasels seem to kill for the mere love of killing, and while occasionally this trait makes them formidable in the poultry house, it also renders them more efficient as destroyers of rodents. A small weasel can follow a rat into all its retreats, and will soon clear a stackyard or shed of all rodents.

167Our largest weasel, the black-footed ferret (Putorius nigripes), occasionally deserts its wild haunts on the plains and comes about buildings in search of rats and mice. In 1905, while the writer was at Hays, Kans., one of these ferrets took up its quarters under a board sidewalk in the business part of the village. The squealing of the rats it killed was often heard.

As regards the destruction of poultry by weasels, the same care necessary to exclude the rat from a poultry house will keep out the weasel also. When so excluded, a weasel will do no harm about the premises, but may be depended upon to drive out or kill all the rats and mice.

MINKS.

Minks are excellent ratters, but as enemies of poultry are worse than weasels. They destroy fish also. The great demand for mink fur causes close trapping of these animals, and in the future they are not likely to influence greatly the numbers of rodent pests.

DOMESTIC ANIMALS.

Among the enemies of rodents often employed as aids to rat destruction are the dog, cat, and ferret.

DOGS.

The value of dogs as ratters can not be appreciated by those who have had no experience with trained animals. The ordinary cur and the larger breeds of dogs seldom make useful ratters. Small Irish, Scotch, and fox terriers, when well trained, are superior to most other breeds as ratters, and under favorable circumstances may be depended on to keep premises free from rodents. Much, too, may be done by the farmer or householder to increase the effectiveness of his dogs by removing obstructions to their work. Corncribs and outbuildings, when of wood, should not have floors close to the ground, but should have ample room below to permit dogs to move about freely.

With a little preliminary training, most terriers learn to hunt rats independently, and they thus become doubly useful on farms and in warehouses.

CATS.

When the black rat was the dominant species in Europe and America, cats were the chief dependence of the householder against rats; but comparatively few cats will venture to capture a full-grown brown rat. Then, too, the ordinary house cat is too well fed and consequently too lazy to be an efficient ratter.

Occasionally, however, one meets with rat-killing cats whose work in destroying the brown rat has decided value. These cats are 168rarely of the fine breeds, but generally of the common “tabby” variety, kept in barns or warehouses, fed on milk, and left to forage for their own meat. Managed in this way, cats are far less objectionable on sanitary grounds than when kept in the house as pets. In the country, on the other hand, barn cats are far more likely than the house-kept ones to run at large and prey upon birds and young poultry. Aside from the rat itself, we have no more serious enemy of birds and game than half-wild cats, many of which have been abandoned in fields and woods by the thoughtless. All things considered, cats do not rank high as destroyers of the common brown rat.

FERRETS.

Tame ferrets, like weasels, are inveterate foes of rats, and can follow them into their retreats. Under favorable circumstances ferrets are useful aids to the rat catcher, but their value is often greatly overestimated. They require experienced handling and the additional services of a well-trained dog or two to do effective work. Dogs and ferrets must be thoroughly accustomed to each other. A noisy or excitable dog is useless in ferreting. The ferret should be used only to drive out the rats, which are then killed by the dogs. If an unmuzzled ferret is sent into rat retreats under floors, it is apt to lie up after killing a rat and sucking its blood. Sometimes the ferret will remain for hours in a rat burrow or escape by unguarded exits and be lost.

Such experiences often discourage the amateur ferreter. Besides, ferrets are subject to diseases and require the greatest of care as to their food. For these reasons the use of ferrets to destroy rats, except in the hands of the experienced, is generally expensive and disappointing.

OTHER ANIMALS.

MONGOOSE.

The various species of mongoose (Herpestes and Mongos) are destroyers of rats, and their importation into this country has often been urged. Many years ago they were introduced into Jamaica and Hawaii to save the sugar plantations from ravages by rats. The mongoose has, however, proved very destructive to native birds and poultry in the islands, and its introduction is now generally regretted. Its importation into the United States is prohibited by law.

ALLIGATORS.

In the South the alligator is said to destroy many rats along levees and banks of streams, and its protection has been urged on this account.

169 SNAKES.

Our larger snakes are beneficial in destroying rats, mice, prairie squirrels, and pocket gophers. As most of the food of snakes is obtained remote from human abodes, only a small percentage consists of rats.

BOUNTIES ON PREDATORY ANIMALS.

Whatever may be said in favor of bounties on the larger beasts of prey, those on hawks, owls, and the smaller fur-bearing animals can not be justified. Payments of this sort should cease, and laws should be enacted to protect species which careful investigations have shown to be mainly beneficial.

A few States still pay bounties for the destruction of foxes, weasels, skunks, minks, and raccoons. All of these, except the southern weasels, have valuable fur, and hence should be protected as a source of wealth. In addition they do far more good by destroying rats, mice, and other field pests than harm to game and poultry.

The payment of bounties on hawks of any kind is open to the objection that officials hardly ever discriminate between the harmful and the useful kinds, even when the statutes do so. Since the beneficial kinds are the more easily captured, public money is often paid out to reward what really injures the community. The bounty on owls is still more reprehensible, since owls are a more decided check to rodent increase.

The natural enemies of the rat exercise a steady, cumulative effect in restricting the numbers of the pest. That the effect is not greater is largely our own fault, since instead of protecting the birds and mammals that prey on the rat, we destroy them, sometimes even offering bounties on their heads. In future our aim should be to increase their numbers and to protect them in every way possible.

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