Rapid ecological release of anti-predator behaviour after island-wide predator control

Abstract Predator–prey interactions can stabilize ecosystems, but these systems are at risk of destabilization when introduced predators alter prey species’ anti-predator behaviour and escape probability. Despite an increase in the removal of invasive predators, we lack information on how invasive predator removal can alter the behaviour of prey species. In particular, escape behaviour has been a focus of population-level studies to measure response to novel predators. In late 2023, a campaign led by the Galápagos National Park Directorate implemented the eradication of black rats ( Rattus rattus ), house mice ( Mus musculus ), and feral cats ( Felis catus ) from Floreana Island, Galápagos, and temporarily removed Galápagos short-eared owls ( Asio flammeus galapagoensis ) to mitigate non-target mortality. In this study, we quantified escape behaviour (flight initiation distance) in four species of Darwin’s finches before (2023) and after (2024) the eradication. We found that flight initiation distance was highly repeatable in colour-banded birds. After predator removal, mean flight initiation distance decreased for one Darwin’s finch species, the common cactus finch ( Geospiza scandens ), while across all species the distribution of flight initiation distances shifted from bimodal to unimodal. The variability in flight initiation distance also increased: there were more extreme responses and fewer ‘intermediate’ responses, with the majority of responses being bold in 2024. The rapid ecological release of extreme anti-predator phenotypes occurred after an abrupt change in predation risk. The ecological restoration of Floreana Island creates an opportunity to study how predator species influence anti-predator behaviour within and across species. Future studies should interrogate if these rapid shifts in escape behaviour are due to phenotypic plasticity or natural selection.