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Fast food in the city? Nomadic flying-foxes commute less and hang around for longer in urban areas

Citation

Meade, Jessica; Martin, John; Welbergen, Justin (2021), Fast food in the city? Nomadic flying-foxes commute less and hang around for longer in urban areas, Dryad, Dataset, https://doi.org/10.5061/dryad.931zcrjk9

Abstract

Urbanization creates novel ecological spaces where some species thrive. Geographical urbanization promotes human-wildlife conflict; however, we know relatively little about the drivers of biological urbanization, which poses impediments for sound wildlife management and conservation action. Flying-foxes are extremely mobile and move nomadically in response to flowering resources, but are now increasingly found in urban areas, for reasons that are poorly understood. To investigate the mechanisms behind flying-fox urbanization, we examined the movement of 99 satellite tracked grey-headed flying-foxes (Pteropus poliocephalus) over one year in urban versus non-urban environments. We found that tracked individuals preferentially visited major-urban roosts, exhibited higher fidelity to major-urban roosts, and foraged over shorter distances when roosting in major-urban areas. In contrast to other colonial species, there were no density-dependent effects of colony size on foraging distance, suggesting that at a landscape scale, flying-foxes distribute themselves across roosts in an ideal-free manner, minimising competition over urban and non-urban foraging resources. Yet, males consistently foraged over shorter distances than females, suggesting that at a local scale foraging distances reflect competitive inequalities between individuals. Overall, our study supports the hypothesis that flying-fox urbanization is driven by increased spatiotemporal availability of food resources in urban areas; however, unlike in other species, it is likely a consequence of increased urban visitation by nomadic individuals rather than a subset of the population becoming ‘urban residents’ per se. We discuss the implications of the movement behavior we report for the conservation and management of highly mobile species.

Methods

Data from deployed PPTs were received and managed in a standardized format in Movebank (www.movebank.org/node/2). We were interested in investigating whether movements between roosts varied with seasonal life-history changes in males and females; therefore, we aimed to investigate movements across a calendar year. As the tracked individuals were caught at a colony that was subsequently dispersed (June 2012) we used data collected after July 1st, 2012. The Microwave Telemetry transmitters carried by female flying-foxes remained operational for longer than the GeoTrak transmitters that were deployed on males (see Table 1), and very few transmitters remained active on males after 1 year. To facilitate comparison between the sexes, data were subsetted such that only data transmitted until June 30th, 2013 were included in the analyses, resulting in one calendar year of data. At this time 33 PTTs carried by females and 10 PTTs carried by males were still transmitting data.

Data were subsetted to retain only high- resolution positional fixes (ARGOS location code 2 & 3; Vincent et al., 2002). All positional fixes were classified as daytime or night-time based on local timing of sunrise and sunset (calculated using the R package ‘maptools’; Bivand and Lewin-Koh, 2017); positional fixes were classed as daytime from sunrise to 1 hour before sunset, and night-time from sunset until sunrise. Positional fixes during the 1 hour before local sunset were classed as dusk and discarded. Daytime positional fixes were used to determine roost location. If high-resolution (ARGOS location code 2 or 3) daytime positional fixes occurred within 3.5 km of a known roost (McKeown and Westcott, 2012) animals were assumed to be roosting at that known roost location. Where accurate daytime positional fixes were more than 3.5 km from a known roost location a new roost location was assigned in the center of the cluster of positional fixes. There were over 400 known roosts utilized by grey-headed flying-foxes prior to this study; however, additional roost site locations were identified through satellite telemetry (Welbergen et al., 2020)

Usage Notes

Data consists of 4 csv files of: number of roosts visited, proportion of roosts visited (by urban classification), roost fidelity, and foraging distance.

Funding

Australian Research Council, Award: DP170104272

Australian Research Council, Award: DP110104186