Displaced Rats

Rats are as bad as human beings in some ways. In the latest Journal of Wildlife Management, Dr. John B. Calhoun, of Johns Hopkins, discusses one such aspect of the rat world: the troubles which refugee rats have to put up with when they emigrate.

Dr. Calhoun took a rat census of several adjoining blocks in Baltimore, and trapped and marked many of the native-son rats. Then he released 112 marked alien rats in the center of the middle block. At once there was social strife. Both native rats and aliens scurried around wildly, invading backyards where none had been seen before. Dogs and humans joined the fray. In the first 18 days there were 31 rat casualties.

When things quieted down, Dr. Calhoun went around trapping rats and taking a new census. He calculated that only 18% of the displaced rats had found permanent homes in the block. The rest had been killed or driven to further wanderings about Baltimore.

In a long-established rat community, says Dr. Calhoun, there is very little fighting. Every rat, having tested its strength against its neighbors, knows its social position and stays in it. Newcomers must battle for places in this set order. But since (like human immigrants) they do not know the new country, they are at a disadvantage. When danger threatens, they do not know where to hide. The newcomers do not know the best sources of food, and therefore lose weight and strength.

The native sons, familiar with local conditions, win most of the battles for position in the social order. They force the D.P.s in the rat colony to accept the least desirable territories, where they lead a marginal existence, exposed to hunger and enemies.

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