Can you predict how a movie will end by looking only at a couple of snapshots from some early scenes? That’s what many ecologists have to do to quickly assess whether an animal population is at risk: they need a method to collect data quickly to predict how animal populations will fare in the future. This is especially difficult with animals that live long lives (like a really long movie!), such as whales, sea turtles, and birds of prey.
Here, we used a mathematical model to examine whether two commonly used snapshot metrics for assessing the health of long-lived eagle populations are reliable. And we are glad we did because we found that they are not reliable. Commonly used measures like how many birds are able to breed and how young birds are when they begin to occupy nests do not accurately predict the status of an eagle population unless they are combined with other data such as the birds’ survival rate or how much food and habitat is available to them.