Beyond the role of bats as natural host reservoirs of infectious agents, the impact of viral spillover from other animal species to bats has been neglected. Given the limited virus-host specificity of astroviruses (AstVs) and their propensity for cross-species transmission, we hypothesized that AstVs could be transmitted within animal communities (rodents, birds, and bats) and that native endemic bats may be exposed to viruses hosted by other species. We investigated the presence of AstV RNA in 3,796 biological samples collected in Reunion Island from ( = 3421), an endemic free-tailed bat species, and also from small terrestrial mammals and birds: ( = 146), ( = 74), ( = 36), ( = 99), and ( = 20). We found significant differences in AstV prevalence between species (ranging from 1% ± 1.97% in to 75% ± 18.9% in ) as well as variation of pairwise identity of AstV sequences among host species, with a high diversity in (mean pairwise identity: 53.2% ± 11.2%). Phylogenetic analyses further revealed that AstVs detected in bats did not cluster in a single clade and were genetically related to AstVs found in birds, rodents, pigs, dogs, cats, and reptiles. Our study suggests that bats may be exposed to viruses associated to synanthropic and alien species. Cascade effects of virus spillover toward endemic and endangered bat species need to be fully assessed.IMPORTANCEEpidemiological consequences of cross-species transmission of zoonotic viruses are mostly considered from a health and economic perspective. Virus spillovers resulting from human-introduced species are much less considered, although they may have major consequences on the conservation of endemic and endangered bat species, in particular in an island context. Based on astrovirus detection and sequencing in an endemic bat species and five non-native species on a tropical island, we identified multiple and repeated viral introductions from synanthropic rodents and birds to bats, rather than the opposite. Such findings call for more investigations in these isolated and vulnerable ecosystems to better understand and mitigate the risks associated with pathogen spillovers.