Native and non-native winter foraging resources do not explain Pteropus alecto winter roost occupancy in Queensland, Australia

Abstract

Anthropogenic land use change concurrent with introductions of non-native species alters the abundance and distribution of foraging resources for wildlife. This is particularly concerning when resource bottlenecks for wildlife are linked to spillover of infectious diseases to humans. Hendra virus is a bat-borne pathogen in eastern Australia. Spillovers align with winter food shortages for flying foxes and flying foxes foraging in agriculture or peri-urban lands, as opposed to native forests. It is believed the increased abundance and spatiotemporal reliability of non-native species planted in anthropogenically modified areas compared to native, ephemeral diet species may be a key draw for flying foxes into urban and peri-urban areas. We investigate the explanatory power of environmental factors on the winter roost occupancy of the reservoir for Hendra virus, the black flying fox Pteropus alecto, from 2007-2020 in Queensland, Australia. We measured the extent, spatial aggregation, and annual reliability of typical (i.e. native) and atypical (i.e. non-native) winter habitat species in 20km foraging areas around roosts surveyed by the National Flying Fox Monitoring Program. We find that neither the extent nor the spatial distribution of winter habitats explained black flying fox winter roost presence. Although the establishment of roosts was associated with high reliability for typical winter diet species, the reliability of frequently listed winter diet species surrounding surveyed roosts was not different between roosts that were occupied versus unoccupied in the winter. Significant interactions between lagged weather conditions and winter habitats identified by the best model did not reflect observable differences in patterns of occupancy upon scrutiny. Static measures of winter habitat and weather conditions poorly explained the winter roost occupancy of black flying foxes. Understanding the drivers of flying fox movement and presence requires further investigation before they can be thoughtfully integrated into Hendra spillover prevention efforts and flying fox management.

Keywords: Hendra virus; Pteropus; diet; resource reliability; seasonal habitat.

FIGURE 1

Study area of Queensland, Australia. (A) The country of Australia with the state of Queensland shaded in dark grey. (B) Map of Queensland with black points identifying flying fox roosts surveyed in winter between 2007 and 2020 and blue circles denoting the boundaries of each roost’s 20 km radius foraging buffer. (C) Example roost’s 20 km foraging area, with areas containing typical winter diet species in green and areas without winter diet species in grey.

FIGURE 2

Proportion of Winter Habitats and Moran’s I Values by Black Flying Fox Roost Occupancy. (A) The proportion of winter habitat extent in roosts’ 20km foraging buffers, for roosts where black flying foxes and grey-headed flying were absent (left) and present (right) in winter months from 2007–2020. (B) Black and grey-headed flying fox absence and presence in summer months, 2007–2020.

FIGURE 3

Annual reliability scores of the most frequent typical winter diet species in roost foraging areas, plotted by roost occupancy, and randomly generated points. (A) Map of Queensland identifying flying fox roosts surveyed in winter between 2007 and 2020 (green circles), roosts not surveyed in winter (orange circles), randomly generated points (light purple circles), and the randomly generated points analyzed (dark purple circles) with the hull of flying fox roosts outlined in black. Empty circles around roosts denote the 20km foraging area. (B) Frequency of fruiting or flowering for the six most prevalent winter diet species in a 20km radius buffer around flying fox roosts (green, orange) and randomly generated points (purple) in the geometric hull around all roosts. (C) Violin plots of the annual reliability score of typical winter diet species in roosts that were unoccupied (light grey) and occupied (dark grey) in the winter.