Figure 1: Probability that a randomly selected bird species occurring in each 50x50 km grid cell is impacted by hunting and trapping. A value of 0 indicates that no species is affected, while a value of 1 indicates that all species are affected. Grey areas indicate areas with fewer than ten species for which the impact probability has not been calculated

Figure from Harfoot et al. 2021, licensed under CC BY 4.0

Biodiversity loss is driven by multiple threats, such as agriculture, hunting and trapping, logging, pollution, invasive species and climate change. For some of these threats, information on spatial patterns in intensity can be gathered through remote sensing. For example, satellite imagery can be used to monitor patterns and rates of deforestation, providing an indication of where species may be particularly threatened by logging. However, remote sensing cannot be used to gather data on pressures such as overexploitation, pollution and invasive species. Even for threats for which remote sensing data are available, these measure the distribution and potential intensity of the threatening process rather than the impact it has on species. Improving our knowledge of how threats and impacts on species are distributed around the globe is crucial for improving conservation responses.

All 11,000+ bird species have been assessed against the Categories and Criteria for the IUCN Red List of Threatened Species. As part of this assessment process, experts evaluate the threats affecting individual species across their global range using standardized methods. In a novel approach to threat mapping, Harfoot et al. (2021) used these data to model the global distribution of the impacts of the top six threats to terrestrial vertebrates. To do so, the ‘impact probability’ was estimated – the probability that a randomly selected species occurring in a given grid cell would be impacted in that cell by a particular threat.

The threat with the highest probability of impact in each cell

Figure from Harfoot et al. 2021, licensed under CC BY 4.0

The results show that hunting and trapping is the most prevalent threat to birds, with a high probability of species being impacted by this threat across most of the mapped range (Figure 1), and hunting and trapping having the highest impact probability of all threats in half of all grid cells (Figure 2). Particularly high probabilities of impact are found throughout northern Africa, Europe and Asia. Agriculture has the highest impact probability across much of South America, while the polar regions, eastern Australia and South Africa show the highest impact probabilities for climate change (Figure 2). The average impact probability of pollution and invasive species is low, although for the latter it is much higher on islands. The islands of Southeast Asia and Madagascar exhibit high probabilities of impact across all threats.

Spatial data on the impacts of threats are crucial for prioritising conservation actions. These data can be combined with information on species richness to identify hotspots of conservation risk, where large numbers of species are exposed to a high probability of a threat. Such areas can then be prioritised for threat mitigation. This approach can also help to identify data-poor areas in which increased sampling effort is needed to improve our understanding of threats to species.