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Meadow Mice Invade Klamath Basin in 1957-58

It was called everything from irruption and infestation to invasion and overpopulation.  Whatever the word, the Klamath and Tule Lake basins had as many as 3,000 to 4,000 meadow mice per acre in 1957-1958.  The cause of the rodent outbreak remains unknown.

The mice ate every tendril in the fields, nested inside potatoes, and tunneled through irrigation banks, causing extensive damage and crop loss.  Fruit trees were girdled and died.  Excrement fouled hay bales.   Many mice were infected with Tularemia, presenting a risk of transmission to humans.  Raptor and gull predator populations swelled in response to the increased food supply, not keeping the irruption in check, but they may have contributed to its decline.

Poison reduced the mouse population, including more than 171,000 pounds of zinc phosphide-treated bait and 28,000 pounds of strychnine-poisoned oat groats applied to 70,000 acres in five counties.  The poison spread to other wildlife that ate the bait.  White-fronted and snow geese were particularly vulnerable as were game birds such as pheasants and quail and waterfowl such as Canadian geese, widgeon, and mallard ducks.

Less invasive poisons have continued to manage rodent populations with no significant problem in the region since 1958.
 

Sources:  The Oregon meadow mouse irruption of 1957-1958; a collection of reports from several agencies on various aspects of the irruption. Corvallis, Ore., Oregon State University, Extension Service, 1959; "Plan for Mouse Poisoning Gets OK at KF Meeting." Herald and News, 25 Mar. 1958 [Klamath Falls, Ore.], p. 1.