Black swan

Improbable ‘black swan’ events can devastate animal populations

black swan
Like black swans, black swan events are rare. But for animal populations, they can be devastating. That’s why conservation managers need to keep them in mind, a new study argues.

Sometimes, the improbable happens. The stock market crashes. A big earthquake shakes a city. A nuclear power plant has a meltdown. These seemingly unpredictable, rare incidents — dubbed black swan events — may be unlikely to happen on any specific day, but they do occur. And even though they may be rare, we take precautions. A smart investor balances their portfolio. A California homeowner stores an earthquake preparedness kit in the closet. A power plant designer builds in layers of safeguards.

Conservation managers should be doing the same thing, scientists warn. Black swan events happen among animals, too, and they rarely have positive effects, a new study finds.

How often do black swan events impact animals? To find out, Sean Anderson of the University of Washington in Seattle and colleagues looked at data for 609 populations of birds, mammals and insects. Often, the data were noisy; there could be lots of ups and downs in population sizes, not always with good explanations for what happened. But, Anderson notes, “it turns out that there are plenty of black swan events that are so extreme that we can easily detect them with available data.”

The researchers looked for upswings or…