The unique size, isolation, and microclimatic/geomorphological conditions of oceanic islands often lead to significant evolutionary divergence and high rates of endemism (Emerson, 2002; Kier et al., 2009). They often act as evolutionary reservoirs for lineages that have disappeared elsewhere and, as such, are crucial for the fate of biodiversity in the Anthropocene (Russell and Kueffer, 2019; Nori et al., 2022). However, historical and ongoing human-induced environmental degradation have resulted in acute changes to island biotas (Nogué et al., 2021). Consequently, ca. 50 % of the planet's terrestrial vertebrates are island dwellers (Leclerc et al., 2018), and most recorded extinctions since the expansion of Europeans have occurred in islands (Blackburn et al., 2004; Fernández-Palacios et al., 2021; Matthews et al., 2022).

Of over 1400 currently recognised bat species, ca. 25 % are island endemics (Conenna et al., 2017). Of these, over 60 % of the bats currently assessed by the International Union for Conservation of Nature (IUCN) are species formerly classified as “microbats”, i.e. laryngeal echolocating bats (Conenna et al., 2017; Frick et al., 2020). Similarly to their mainland counterparts, some island-dwelling microbats are seed dispersers and pollinators (Ramirez-Francel et al., 2021). However, most species are insectivores and potentially play pivotal roles in the suppression of arthropods, including agricultural pests and mosquitoes (Kemp et al., 2019). More than one-fourth of these laryngeal echolocating bats are assessed as CR, EN, or VU by the IUCN Red List, largely due to the additive and often synergistic effects of habitat loss and fragmentation, as well as the impacts of invasive species (Rodríguez-Durán et al., 2010; Conenna et al., 2017).

The Macaronesian biogeographical region, composed of the archipelagos of the Azores, Madeira, Selvagens Islands, Canary Islands, and Cabo Verde, is home to at least 15 bat species, including three island-restricted ones, namely the Azores noctule Nyctalus azoreum, the Canary big-eared bat Plecotus teneriffae, and the Madeiran pipistrelle Pipistrellus maderensis (Gonzáles-Dionis et al., 2022). The latter is a relatively small bat (forearm length = 29.5–34.0  mm) likely derived from African Pipistrellus kuhlii that colonised the Canary Islands and the archipelago of Madeira (Pestano et al., 2003) or from a common ancestor to both species (Jesus et al., 2013). It is a synanthropic species with flexible habitat requirements, being found in the archipelagos of Madeira, the Canary Islands, and possibly Azores (Trujillo and Gonzalez, 2011; Rainho, 2022; Rocha, 2021; Rainho et al., 2002). The species seems to be more abundant at lower altitudes, occurring in a variety of natural and humanised habitats, such as native forests and agricultural and urban areas (Teixeira and Jesus, 2009; Jesus et al., 2009; Ferreira et al., 2022; Nouioua, 2022; Rocha, 2021). It feeds on a wide diversity of arthropods (Gonçalves, 2022) and is prone to roost in cliffs, tree holes, and a variety of human-made structures such as bridges and tunnels (Rocha, 2021).

Pipistrellus maderensis is listed by the IUCN as vulnerable (Alcalde and Juste, 2016) and is one of Europe's most threatened bat species. Its geographic isolation and fragmented populations, typical of insular species, make it particularly vulnerable to anthropogenic stressors and natural catastrophes (Rocha, 2021). The threats to the conservation of aerial insectivorous bats such as Pipistrellus spp. are numerous, and since they are small, mostly nocturnal, and inconspicuous, their population declines often go unnoticed. As an extreme example, the last known Christmas Island pipistrelle Pipistrellus murrayi disappeared in 2009, becoming the first animal to go extinct in Australia in the last 5 decades (Woinarski, 2018). In Madeira, where it is more abundant, the population was suggested to be smaller than 1000 individuals (Cabral et al., 2005), whereas Azores might be home to fewer than 300 individuals (Queiroz et al., 2005).

Although Pipistrellus maderensis were known to occur in Porto Santo (archipelago of Madeira), previous surveys failed to detect the species (Jesus et al., 2013). However, it is unclear if the method and intensity of the surveys were sufficient to prove the absence of the species in the island. Here, we combine bioacoustics, phylogenetic analysis, and DNA metabarcoding to investigate the population status, evolutionary history, and trophic interactions of Pipistrellus maderensis in Porto Santo. Specifically, we address the following questions.

Is Porto Santo still home to an extant population of Pipistrellus maderensis? We anticipate that Pipistrellus maderensis still persists in Porto Santo, and we predict that considering the xeric climate of the island, bat activity is likely to be strongly influenced by artificial water sources.

During our bioacoustic survey we detected bats in 28 out of the 46 sampling sites (60 %; Table S2). In total, we identified 7797 bat passes of Pipistrellus maderensis in our recordings. Furthermore, we mist-netted six individuals (including three juveniles and one lactating female; Fig. S1; Table S4). All captures occurred at ca. 260 m a.s.l., in forest trails near Pico Castelo. No other bat species were detected.

Lack of baseline knowledge is a key constraint for the development of management strategies for the conservation of insectivorous bats and for maximising any ecosystem services they might provide. Here, we show that Porto Santo is still home to an extant population of Pipistrellus maderensis and provide much-needed information about their habitat affinities, phylogenetic kinship, and trophic interactions.

Bats are known to present marked responses to landscape features in both island and non-island ecosystems (Ancillotto et al., 2023; López-Baucells et al., 2021). In the nearby island of Madeira, Pipistrellus maderensis was found to be particularly associated with shrubland, agricultural areas, and Laurisilva (primary) forest (Ferreira et al., 2022). However, in Porto Santo and probably as an artefact of the small dimensions of the island, in which multiple land-use covers converge within relatively short distances, we were unable to detect these associations. Yet, consistent with previous studies (Ancillotto et al., 2019; Moretto et al., 2023; Torrent et al., 2018), we have found that bat activity was positively associated with artificial water reservoirs such as dams and urban ponds. Water limitations and unpredictability in precipitation, typical of xeric climates such as the one characterising Porto Santo (Maestre et al., 2016), pose important challenges to insectivorous bats (Conenna et al., 2021). Our results indicate that in Porto Santo artificial water sources likely provide important drinking and foraging resources for Pipistrellus maderensis, potentially reducing spatiotemporal variations in food availability. However, it is important to note that our bioacoustic survey was conducted over ca. 1 week – too short of a period to be able to capture complex bat activity variations, which can be affected by multiple factors, including lunar phase and season (Appel et al., 2021; Gorman et al., 2021).

The evolutionary history of insular species is often shaped by the geographic separation of different island populations (e.g. Recuerda et al., 2021). Previous molecular phylogenetic analyses suggested the existence of at least three lineages of Pipistrellus maderensis in the Canary Islands (Pestano et al., 2003) and one in Madeira (Jesus et al., 2013). Indeed, there is no haplotype sharing between Pipistrellus maderensis from both archipelagos, suggesting that they represent distinct evolutionary lineages, albeit not distinct enough to constitute different species (Jesus et al., 2013). Our results indicate a close phylogenetic affinity between the Pipistrellus maderensis from Porto Santo and Madeira (only 0.04 % genetic distance; Fig. 3), indicating that the ca. 40 km separating the two islands has not led to considerable genetic divergence between both populations.

Due to their capacity to fly, geographical barriers, such as large expanses of ocean, do not necessarily represent effective barriers to gene flow among bat populations (García-Mudarra et al., 2009). Yet, molecular studies revealed limited overwater dispersal of Nyctalus azoreum between some islands of the archipelago of the Azores (Salgueiro et al., 2008). Likewise, while dispersal and gene flow of Hypsugo savii among some of the closest islands (> 40 km) of the Canary Islands is frequent, gene flow is rare among Canarian populations of Pipistrellus maderensis inhabiting different islands (Pestano et al., 2003). The low genetic divergence between the populations of Pipistrellus maderensis of Porto Santo and Madeira suggests gene flow between both islands. However, this might also be due to a relatively recent (re)colonisation of Porto Santo, with individuals from Madeira. In fact, Porto Santo was heavily impacted by human-induced habitat change, which combined with the effects of invasive species might have led to the decline in the abundance – and possible extinction – of Pipistrellus maderensis and possibly other bat species, which would mimic patterns of anthropogenic extinctions observed in other vertebrate groups (e.g. Alcover et al., 2015).

DNA metabarcoding allows unprecedented resolution in the assessment of the diet of insectivorous predators. Although we were only able to sample and analyse faecal samples from four individuals, we detected prey items belonging to five insect orders, corresponding to at least 11 different species. In Madeira, a recent study identified Lepidoptera as the most consumed order by Pipistrellus maderensis (Gonçalves, 2022). However, Diptera was the most represented order in the four samples analysed from Porto Santo (Fig. 4). These results align with findings for Pipistrellus kuhlii (a sister taxa of P. maderensis) in the Iberian Peninsula, where Diptera has been found to make up over half of the species' diet (Goiti et al., 2003). Hymenoptera, Lepidoptera, Hemiptera, and Neuroptera were also detected in the diet of Pipistrellus maderensis in this study, which in combination with the identification of Coleoptera, Tipulidae, Chironomidae, and Aranea in the diet of the species in Madeira (Gonçalves, 2022) suggests that, similarly to Pipistrellus kuhlii (Amichai and Korine, 2020), Pipistrellus maderensis is likely a “selective opportunist” that feeds on a wide variety of prey, according to its availability. Despite the reduced sample size of our diet analyses, we detected at least four known or potential economically important insect pest species (e.g. Epiphyas postvittana, which is known to damage the fruits of multiple species; Danthanarayana et al., 1975; Thrimawithana et al., 2022) and two mosquitoes known to be vectors of human and non-human diseases (e.g. Culex pipiens, which can spread avian malaria; Hamer et al., 2008; Fros et al., 2015) (Table 1). The high percentage of known or potential agricultural pest species and of species of health relevance consumed by Pipistrellus maderensis highlights the potential role of insectivorous bats as suppressors of arthropods with negative economic and (both human and non-human) disease implications (Montauban et al., 2021; Ancillotto et al., 2022, 2023; Ferreira et al., 2023).

Insectivorous bats are often not considered as charismatic as other island vertebrates, and their conservation is neglected. The population of Pipistrellus maderensis from Porto Santo, despite being genetically similar to the one inhabiting Madeira, is of critical importance to the ecological balance, acting as a predator of a multitude of arthropod species. The bats were detected throughout most of the island, but the extant population appears to be small and thus particularly vulnerable to threat factors such as the destruction of roost and feeding habitats, reduction of prey due to pesticide use, or the impacts of invasive species (e.g. free-ranging cats Felis catus, a known predator of Pipistrellus maderensis; Rocha, 2015). We urge that more research is devoted to this population, which represents the sole native terrestrial mammal of Porto Santo.