Mass die-offs are individual events that kill at least a billion animals, wipe out over 90 percent of a population, or destroy 700 million tons-the equivalent weight of roughly 1,900 Empire State Buildings-worth of animals. According to new research, such die-offs are on the rise. The study, published this week in the Proceedings of the National Academy of Sciences, is the first to examine whether mass die-offs have increased over time. Researchers reviewed historical records of 727 mass die-offs from 1940 to 2012 and found that over that time, these events have become more common for birds, marine invertebrates, and fish. Disease, human-caused disturbances, and biotoxins ... are three major culprits. Big die-offs can permanently change food webs. Massive die-offs can also endanger human activities like farming by disrupting insects that pollinate plants, like bees. "Such events can reshape the ecological and evolutionary trajectories of life on Earth," the study authors write. It's unclear what's making diseases more common. Climate change and environmental degradation are some contenders. Researchers also don't know why die-off rates differ between animal groups. What's clear is that lack of coordinated attention from scientists is a problem, the study authors say. There needs to be better monitoring of these events.