When we think of the rapid growth of humans and their impact on nature, usually animal species are negatively affected by such changes including loss of habitat, local extinction, and increased pollution. However, the rise in widespread urbanization has granted some species the ability to thrive. While this may promote human-wildlife interactions, conflict can arise involving property damage, human or animal injuries, and fear of transmittable diseases from animals. Recently, one such species, the gray flying-fox bat has made its presence known with increasing rates in urban locations. This highly mobile and nomadic species for reasons unknown, seems to flourish in urban environments. A research team headed by Meade and colleagues sought to determine the driving force(s) for flying-fox urbanization by satellite tracking 99 gray-headed flying foxes (Pteropus poliocephalus) over the span of a year in urban and non-urban environments. Since some features of flying-foxes are different depending on sex, with adult males on average being 19% heavier than female counterparts and having slightly larger (2-4%) skeletal dimensions, researchers proposed a probable difference in competition for foraging and preferred place of rest, or otherwise known as a roost. Further, seasons were taken into account when collecting data with implications dependent on the time of year for each sex; females undergoing the energetically expensive process of lactation in spring (September to November) and summer (December to February) whereas males were faced with high energy demands defending territories during autumn (March to May) mating season.
Samples were caught initially in the urban area of the Royal Botanic Garden, in Sydney, Australia, and viable samples were then mounted with collar transmitters. These transmitters had active periods of 10 hours and were given a period of inactivity to recharge. The position of flying-foxes during the day (when resting) allowed scientists to ascertain location of roosts which were classified as major-urban (100,000 >), minor-urban (1,000 to 99,999), or non-urban (other) entirely dependent on population and dwelling density of nearby environment. Depending on the number of repeated visits, they were able to survey flying-bat fidelity to particular roosts and likelihood to leave. In addition, foraging distances were traced during active hours (nighttime) to deduce whether roost type was influenced by sex, time of year, and colony size of roost.
Throughout the course of a year, there were 302 visited roost sites: 16% major-urban, 16% minor-urban, and 69% non-urban. Then, scientists examined the visitations to roost sites by males and females and found males visited almost twice as many major-urban areas than other areas, whereas females proportionally visited around similar levels. This preference by males for major-urban roosts suggests that colonies present, may likely favor male compositions. Both female and male flying-foxes exhibited high fidelity (faithfulness) towards major-urban roosts over other types. Moreover, foraging distances observed in major-urban roosts were shown to fly shorter distances than other roost types. As for intervals of high energy expenditure, females during lactation (the summer) had greater foraging distances and male foraging distances were shorter during the breeding season to defend territories. Overall males consistently foraged shorter distances than females, indicating a competitive inequality between individuals of different sexes.
As for the driving force of urbanization among flying-foxes, Meade and colleagues suggest this is a result of optimal foraging, where individuals maximize their net energy gain with reduced foraging distance and accessibility to abundant resources, though more research is required to confirm the stability of urban food resources.
References:
Jessica Meade, John M Martin, Justin A Welbergen, Fast food in the city? Nomadic flying-foxes commute less and hang around for longer in urban areas, Behavioral Ecology, Volume 32, Issue 6, November/December 2021, Pages 1151–1162, https://doi.org/10.1093/beheco/arab078
