In the evening, they would pour out of the crevices in the stadium in search of their nightly repast. However, during the day they deposited prodigious quantities of guano on the bleachers while hanging sleepily from the stadium canopy. Maintenance crews had to pressureclean the stadium twice a day to make it habitable - or sittable - for the fans.
Although the bats were a nuisance in some respects, they were also a valuable resource because they consumed tons of pesky mosquitos. Without bats (the mammal variety), the Mets would be spending more on insect control and less on guano control.
A solution was found by building a new, wooden bat house in a swampy area behind right field. It is now home to some 15,000 bats. Meanwhile, the bleachers are guano-free and nature's mosquito control program is working efficiently and economically.

Founded 30 years ago in Bozeman, Montana, PERC—the Property and Environment Research Center—is the nation’s oldest and largest institute dedicated to improving environmental quality through property rights and markets.
PERC’s publications, each designed to resonate with specific groups, move ideas generated at PERC to broader audiences.
Research is at the heart of PERC's work, with a focus on the question: What is the link between economic growth and environmental quality?
The goal of PERC’s programs is to fully realize the vision of establishing “PERC University,” where scholars, students, policy makers, and others convene to expand the applications of free market environmentalism.
PERC's fellowships share a common goal of exposing new scholars, students, journalists, and policy makers to free market environmentalism, as well as enable scholars already familiar with FME to explore new applications.
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