If you’re afraid of normal-sized rats and mice, you’re probably terrified of really big rats and mice. Not those cute South American capybaras in the zoo that look like gerbil balloons. We’re talking sewer rats that can lift their own manhole covers. Field mice big enough to drive tractors with cheese wheels. If those kind of rodents give you the creeps, you should stay away from islands where the main inhabitants are rodents and rodent food.
That’s the conclusion of Duke University biologists Paul Durst and Louise Roth whose rodent research appears in the current Proceedings of the Royal Society B: Biological Sciences. They studied the populations of 182 islands and found that the various rodent species there were regularly in the top 2.5 percent of sizes of all rodents.
When it comes to island rats and hamsters, how big is big? The Coues' rice rat on the island of Cozumel is twice as big as the same mice in Mexico. Deer mice on the Gulf Islands are twice as big as deer mice in Vancouver. The St. Kilda field mouse on the Scottish island of St. Kilda is double the size of mainland field mice. The Flores giant rat on the Indonesian island of Flores can be 17.7 inches long with an additional 27.5 inches of tail, making it twice the size of the average brown rat. The same is true on most other islands.
This is the first study to find that rodents follow what is known as the “island rule” which predicts that small animals living on isolated islands grow larger and large animals grow smaller than their mainland counterparts. For the island rodents, abundant food, lack of predators and the need to defend their territory are the most likely causes for their giant size.
Would the giant island rodents return to normal size if brought back to the mainland? I’m sure the researchers would like to find out … unless they’ve seen “King Kong.”