[MIGRATION OF RATS.]
In nearly all countries a seasonal movement of rats from houses and barns to the open fields occurs in spring, and the return movement takes place as cold weather approaches. The movement is noticeable even in large cities.
More general movements of rats often occur. In 1903 a multitude of migrating rats spread over several counties of western Illinois. They were noticed especially in Mercer and Rock Island Counties. For several years prior to this invasion no abnormal numbers were seen, and their coming was remarkably sudden. An eye-witness to the phenomenon informed the writer that as he was returning to his home by moonlight he heard a general rustling in the field near by, and soon a vast army of rats crossed the road in front of him, all going in one direction. The mass stretched away as far as could be seen in the dim light. These animals remained on the farms and in the villages of the surrounding country, and during the winter and summer of 1904 were a veritable plague. A local newspaper stated that between March 20 and April 20, 1904, F. U. Montgomery, of Preëmption, Mercer County, killed three thousand four hundred and thirty-five rats on his farm. He caught most of them in traps.
In 1877 a similar migration occurred into parts of Saline and Lafayette Counties, Mo., and in 1904 another came under the writer's observation in Kansas River Valley. This valley for the most part was flooded by the great freshet of June, 1903, and for about ten days was covered with several feet of water. It is certain that most of the rats in the valley perished in this flood. In the fall of 1903 much of the district was visited by hordes of rats, which remained during the winter, and by the following spring had so increased in numbers that serious losses of grain and poultry resulted.
No doubt the majority of the so-called migrations of rodents are in reality instances of unusual reproduction or of enforced migration owing to lack of food. In England a general movement of rats inland from the coast occurs every October. This is closely connected with the closing of the herring season. During the fishing the rodents swarm to the coast, attracted by the offal left from cleaning the herring, and when this food supply fails they hasten back to the farms and villages.
In South America periodic plagues of rats have taken place in Parana, Brazil, at intervals of about thirty years, and in Chili at intervals of from fifteen to twenty-five years. These plagues in the cultivated lands follow the ripening and decay of the dominant species of bamboo in each country. The ripening of the seed furnishes for two or more years a favorite food for rats in the forests, where the animals multiply greatly; when this food fails they are forced to the cultivated districts for subsistence. In 1878 almost the entire crops of corn, rice, and mandioca in the State of Parana were destroyed by rats, causing a serious famine.
An invasion of black rats in the Bermuda Islands occurred about the year 1615. In a space of two years they had increased so alarmingly that none of the islands was free from them. The rodents devoured everything which came in their way—fruit, plants, and even trees—so that for two years the people were destitute of bread. A law was passed requiring every man in the islands to set twelve traps. In spite of all efforts the animals increased, until they finally disappeared with a suddenness which could have resulted only from a pestilence.