We all know that population vary over time, but also between locations. However, the changes in some locations can be more similar to each other than the changes at other locations, that is the ups and downs over time tend to be more closely matched. This is known as ‘synchrony’, when the population does well at one site, it does well at others, and similarly they tend to dip at the same time. There can be a number of reasons why this might occur, including similar changes in habitat, or weather, or simply populations might be linked by dispersing individuals. Understanding these patterns can help in the design of conservation strategies by helping better target scarce resources to where they might be most effective.