Aim

To assess how environmental characteristics and human impacts contribute to the global prevalence of threatened bird species on islands globally, and to identify which types of anthropogenic land use are most strongly associated with extinction risk on islands.

Location

Global

Time period

Present-day extant species and land-use patterns

Major taxa studied

Terrestrial birds

Methods

We compiled bird species occurrence and conservation status data from BirdLife International and eBird, alongside environmental and land-use variables for islands. We grouped nine predictor variables into three categories: island characteristics (e.g., area, isolation, climate), human impacts (urban cover, cropland, human appropriation of NPP), and wildlands (intact habitat). Using model selection and BIC-based model weights, we evaluated the relative support for each variable group and assessed which factors best explained the prevalence of threatened species (i.e., the proportion of threatened to non-threatened species per island).

Results

Models including both island characteristics and human impact variables explained ~40% of the variation in the prevalence of currently threatened bird species across islands. The strongest predictor overall was island type: oceanic islands exhibited significantly higher threatened species prevalence than continental islands. Among human impact variables, urban land cover had the most substantial effect, with highly urbanized islands showing up to a five-fold increase in threatened species prevalence.

Main conclusions

The prevalence of currently threatened species across islands is shaped by the interplay between environmental conditions and anthropogenic pressures. Our findings highlight urbanization as a particularly potent driver of extinction risk, especially on oceanic islands. This study underscores the need to update island biogeography frameworks to explicitly account for human-driven impacts, as island ecosystems are increasingly reshaped by global land-use transformations.