In a world where the money available for conservation is never enough, we need to prioritise which species we choose to conserve. One of the main ways this is done is to work out the extinction risk for each species (e.g., IUCN Red List) and then spend money on the ones most likely to disappear. But we often don’t have very much information to help us decide how at risk a species is, and so just base the decision on the area of its distribution (geographic range size), with the idea being that species with a small distribution are more at risk than those that occupy a big area. However many species move around and these movements can lead to substantial temporary expansion and contraction of geographic ranges, to levels which may pose an extinction risk. For instance, nomadic birds can contract down to very small areas during time of drought and this makes them very vulnerable to threats during that time.
In this paper we modelled the dynamic distributions of 43 arid-zone nomadic bird species across the Australian continent for each month over 11 years and calculated minimum range size and extent of fluctuation in geographic range size from these models. There was enormous variability in predicted spatial distribution over time; during times of poor environmental conditions, several species not currently classified as globally threatened contracted their ranges to very small areas, despite their normally large geographic range size. This finding raises questions about the adequacy of conventional assessments of extinction risk based on static geographic range size (e.g., IUCN Red Listing). Our approach provides a tool for discovering spatial dynamics in data-poor and highly mobile species and can be used to unlock valuable information for improved extinction risk assessment and conservation planning.