Foraging habitat quality of an Endangered mass-culled flying fox is reduced by alien plant invasion and improved by alien plant control

Abstract

Biodiversity is facing an extinction crisis due to human activities, including loss of seed dispersal function due to frugivores’ extinction or rarefaction. Among these frugivores, flying foxes emerge as major seed disseminators of native plants thereby contributing in maintaining forest structure and biodiversity. However, they are often persecuted because of the inclusion of commercial fruits into their diet, and such a human-wildlife conflict (HWC) may reach extreme levels as exemplified on Mauritius where the species has been subjected to repeated mass culling campaigns. It therefore matters to investigate how bat damages to commercial fruits may be mitigated, including through improving native foraging habitat quality. We investigated both the influence of different severity of alien plant invasion and the influence of invasive alien plants (IAP) control on flying fox foraging habitat quality. This was measured through quantification of foraging bat density (using quadcopter-mounted thermal camera) and through the assessment of feeding intensity using ejecta sampling. We assessed native tree density from different habitat grades and also compared flying foxes’ daily roosting colony size with foraging bats’ density. In forests invaded by alien plants, flying foxes’ density was three times higher in better preserved zones (>50% native canopy cover) compared to more degraded ones (<50% native canopy cover). Within native forest of similar relatively high quality (>70% native canopy cover), flying foxes’ density was about three times higher in weeded areas compared to non-weeded ones. Density of bat ejecta sampled on the forest floor follow similar patterns. Foraging bats’ density was strongly positively correlated with nearby bats’ roosting colony size. Better preserved non-weeded forests provide better foraging habitat quality for flying foxes which are able to detect and use fruit, and possibly floral and other resources there. Ecological restoration through IAP removal improves the foraging habitat quality of bats which also tend to roost closer to their foraging grounds presumably to foster optimal foraging. Our work can help earmark valuable native forests for fruit bats during conservation planning, such as in prioritizing areas for IAP removal. This would improve the bats’ foraging habitat through natural increase of food resources and likely reduce their reliance on commercial fruits. Efforts to naturally increase bats' roosting colony size through the protection of roosts located closer to native forests could also encourage flying foxes to stay in and feed more often within their native habitat, potentially alleviating the HWC.