MIGRATION OF RATS.
In nearly all countries a seasonal movement of rats from houses andbarns to the open fields occurs in spring, and the return movementtakes place as cold weather approaches. The movement is noticeable evenin large cities.
More general movements of rats often occur. In 1903 a multitude ofmigrating rats spread over several counties of western Illinois. Theywere noticed especially in Mercer and Rock Island Counties. For severalyears prior to this invasion no abnormal numbers were seen, and theircoming was remarkably sudden. An eye-witness to the phenomenon informedthe writer that as he was returning to his home by moonlight he hearda general rustling in the field near by, and soon a vast army of ratscrossed the road in front of him, all going in one direction. The massstretched away as far as could be seen in the dim light. These animalsremained on the farms and in the villages of the surrounding country,and during the winter and summer of 1904 were a veritable plague. Alocal newspaper stated that between March 20 and April 20, 1904, F. U.Montgomery, of Pre?mption, Mercer County, killed three thousand fourhundred and thirty-five rats on his farm. He caught most of them intraps.
In 1877 a similar migration occurred into parts of Saline and LafayetteCounties, Mo., and in 1904 another came under the writer's observationin Kansas River Valley. This valley for the most part was flooded bythe great freshet of June, 1903, and for about ten days was coveredwith several feet of water. It is certain that most of the rats in thevalley perished in this flood. In the fall of 1903 much of the districtwas visited by hordes of rats, which remained during the winter, and bythe following spring had so increased in numbers that serious losses ofgrain and poultry resulted.
No doubt the majority of the so-called migrations of rodents are inreality instances of unusual reproduction or of enforced migrationowing to lack of food. In England a general movement of rats inlandfrom the coast occurs every October. This is closely connected with theclosing of the herring season. During the fishing the rodents swarm tothe coast, attracted by the offal left from cleaning the herring, andwhen 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 intervalsof from fifteen to twenty-five years. These plagues in the cultivatedlands follow the ripening and decay of the dominant species ofbamboo in each country. The ripening of the seed furnishes for twoor more years a favorite food for rats in the forests, where theanimals multiply greatly; when this food fails they are forced to thecultivated districts for subsistence. In 1878 almost the entire cropsof corn, rice, and mandioca in the State of Parana were destroyed byrats, causing a serious famine.
An invasion of black rats in the Bermuda Islands occurred about theyear 1615. In a space of two years they had increased so alarminglythat none of the islands was free from them. The rodents devouredeverything which came in their way--fruit, plants, and even trees--sothat for two years the people were destitute of bread. A law was passedrequiring every man in the islands to set twelve traps. In spite of allefforts the animals increased, until they finally disappeared with asuddenness which could have resulted only from a pestilence.