Hot Topic

Managing tensions around urban flying-fox roosts

Thursday, 1 January 1970  | 

Flying-foxes are large bats that feed on nectar, pollen and fruit at night, and roost by day in colonies in the thousands. They are amongst the most mobile mammals on Earth and can track changes in floral resources across much of Australia’s north and east, where they are pivotal for pollination and seed dispersal in forests. Populations have experienced declines since European colonisation due to habitat destruction and persecution, and the Grey-headed and the Spectacled flying-fox are listed as threatened nationally.

Flying-fox roosts are now increasingly urban, potentially because of the feeding opportunities these areas provide and loss of habitat elsewhere. This causes community concern because roosting flying-foxes are noisy, smelly, can damage vegetation and property, and are often perceived as carriers of diseases. Concern is exacerbated when local mass flowering leads to the sudden (and often short-term) arrival of thousands of flying-foxes. This is usually interpreted to mean that there has been an overall population increase, causing some to question the species’ protected status and to call for ‘dispersal’ involving the use of disturbances to encourage the bats to move elsewhere. Urban dispersals require sustained effort over long periods, can cost millions of dollars, and typically either fail to move the bats along or force them into even more contentious areas.

There is an urgent need to experimentally test the efficacy of alternative mitigation measures, and to cater local management to the social context of each roost. Approaches currently being trialled include the installation of double-glazing and shade cloth to buffer noise and smell, vegetation pruning and revegetation to increase the distance between roosts and people’s amenity, and education programs to change perceptions. These have the potential to deliver longer-term socially acceptable outcomes.

Research Entries

Title
Aims
Results
Aziz, S. A., Olival, K. J., Bumrungsri, S., Richards, G. C., Racey, P. A. (2015) The conflict between Pteropodid bats and fruit growers: Species, legislation and mitigation. In: Bats in the Anthropocene: Conservation of Bats in a Changing World (eds C. C. Voigt & T. Kingston) pp. 377–426, Springer International Publishing.
Review the literature and current state of the conflict between fruit growers and Pteropodids and describe the wide range of potential mitigation techniques
At least 18 Pteropodid fruit bat species feed on 90 fruit species grown for human consumption. Netting is the only demonstrably effective method of peeventing loss of fruit to bats: evidence for effectiveness of decoy crops, deterrents, and biological control is equivocal.
Dickman, C., Fleming, M. (2002) Pest, or Passenger Pigeon? The New South Wales Scientific Committee’s assessment of the status of the Grey-headed Flying-fox. In: Managing the Grey-headed Flying-fox as a Threatened Species in New South Wales (eds P. Eby & D. Lunney) pp. 20–28, Royal Zoological Society of New South Wales, Mosman NSW.
To chronicle the steps taken in listing the Grey-headed Flying-fox under the NSW TSC Act, and briefly review the evidence on which listing was based.
Based on population counts during three periods (Ratcliffe in the 30s, Parry-Jones in the 90s and Eby in the 90s) it is clear that the Grey-headed Flying-fox is in decline and at a rate that is significant, though these three point estimates have large error bars around them.
Eby, P. (1991) Seasonal movements of grey-headed flying-foxes, Pteropus poliocephalus (Chiroptera : Pteropodidae), from two maternity camps in northern New South Wales. Wildl. Res. 18, 547.
To document the distance and direction that Grey-headed flying-fox adults moved from maternity camps, to determine the extent of movement among camps in the region, and to define the breeding population in the region.
Individuals from Lismore remianed within 50km of the roost, while those from Grafton undertook a large-scale migration (median = 324km)
Eby, P. (1998) An analysis of diet specialization in frugivorous Pteropus poliocephalus (Megachiroptera) in Australian subtropical rainforest. Aust. J. Ecol. 23, 443–456.
To document the fruit diet of P. poliocephalus and constructs a diet list for sympatric frugivorous birds on the basis of published material.
There was no evidence that the Grey-headed flying fox is a specialist feeder and there was substantial dietary overlap with frugivorous birds
Eby, P., Richards, G., Collins, L., Parry-Jones, K. (1999) The distribution, abundance and vulnerability to population reduction of a nomadic nectarivore, the Grey-headed Flying-fox Pteropus poliocephalus in New South Wales, during a period of resource concentration. Aust. Zool. 31, 240–253.
To provide information relevant to an assessment of the conservation status of Grey-headed Flying-foxes in New South Wales by describing the distribution and abundance of the species at a time when food resources were limitedin species composition and distribution, andthe population in the state was concentratedinto small areas
During July 1998 food shortages 99% of GHFF in NSW occurred in 9 coastal camps. Total NSW population at this time estimated to be 85,400.
Eby, P., Lunney, D. (2002) Managing the Grey-headed Flying-fox Pteropus poliocephalus as a threatened species: a context for the debate. In: Managing the Grey-headed Flying-fox as a Threatened Species in New South Wales (eds P. Eby & D. Lunney) pp. 1–15, Royal Zoological Society of New South Wales, Mosman NSW.
To provide context for the debate surrounding the listing of the Grey-headed flying-fox as Threatened in NSW, with particular reference to crop damage.
Grey-headed Flying-foxes are not rare and interactions between flying-foxes and humans are apparently increasing. It is understandably difficult for some people to accept that the future of a species that seems so abundant and capable of adapting to the presence of humans can be in doubt.The level of conflict that arises at flying-fox camps in NSW is consistently related to the distance between roosting animals and areas of human activity, and the numbers of animals in a camp. This is an issue dogged by lack of rigorous investigation and innovation. The open nature of the population of Grey-headed flying-foxes and the geographic scale at which it functions was a revelation that helps to explain the failure of local culling programs to control numbers.
Edson, D., Field, H., McMichael, L., Jordan, D., Kung, N., Mayer, D., Smith, C. (2015) Flying-fox roost disturbance and Hendra virus spillover risk (ed B. S. Schneider). PLoS One. 10, e0125881.
To examine the impact of roost modification and dispersal on Hendra Virus infection dynamics and cortisol concentration dynamics in flying-foxes
The difference in mean Hendra Virus prevalence in samples collected before (4.9%), during (4.7%) and after (3.4%) roost disturbance was small and non-significant. Similarly, the difference in mean urine specific gravity-corrected urinary cortisol concentrations was small and non-significant.
Edson, D., Field, H., McMichael, L., Vidgen, M., Goldspink, L., Broos, A., Melville, D., Kristoffersen, J., de Jong, C., McLaughlin, A., Davis, R., Kung, N., Jordan, D., Kirkland, P., Smith, C. (2015) Routes of hendra virus excretion in naturally-infected flying-foxes: Implications for viral transmission and spillover risk. PLoS One. 10, e0140670.
To identify the major routes of Hendra Virus excretion in naturally infected flying-foxes, and secondarily, to identify between-species variation in excretion prevalence.
Urine as the most plausible source of Hendra infection for flying-foxes and for horses. There were no detections in P. poliocephalus (Grey-headed FF) or P. scapulatus (Little red FF), suggesting that these species are epidemiologically less important than P. alecto (black FF) in Hendra Virus infection dynamics.
Fox, S., Luly, J., Mitchell, C., MacLean, J., Westcott, D. A. (2008) Demographic indications of decline in the spectacled flying fox (Pteropus conspicillatus) on the Atherton Tablelands of northern Queensland. Wildl. Res. 35, 417–424.
To construct a life table for the spectacled flying-fox and provide age estimates based on tooth cementum rings
As a result of high mortality, longevity was much shorter than expected from a theoretical basis. Life-table analyses suggest that the population experienced a 16% decrease during the 2 years of study
Fujita, M. S., Tuttle, M. D. (1991) Flying foxes (Chiroptera: Pteropodidae): Threatened animals of key ecological and economic importance. Conserv. Biol. 5, 455–463.
To document the role of flying foxes in plant propagation.
At least 289 plant species rely to varying degrees on large populations of flying foxes for propagation. These plants, in addition to their many ecological contributions, produce some 448 economically valuable products.
Garnett, S., Whybird, O., Spencer, H. (1999) The conservation status of the spectacled flying fox Pteropus conspicillatus in Australia. Aust. Zool. 31, 38–54.
To conduct a survey of all known Spectacled flying-fox (Pteropus conspicillatus) camps to estimate the current population size
There were about 153,000 spectacled flying foxes across the 12 major camps (low estimate = 120,000, high estimate = 180,000)
Kung, N. Y., Field, H. E., McLaughlin, A., Edson, D., Taylor, M. (2015) Flying-foxes in the Australian urban environment—community attitudes and opinions. One Heal. 1, 24-30.
To capture community attitudes and opinions on flying-foxes in the urban environment to inform management policy and decisionmaking.
A majority of respondents indicated a moderate to high level of knowledge of both flying-foxes and Hendra virus, yet a substantial minority mistakenly believed that flying-foxes pose a direct Hendra virus infection risk to humans. A minority of community members indicated they were directly impacted by urban roosts. Neither dispersal nor cullingwas seen as an appropriate management strategy by the majority of respondents, including those from postcodes where flying-fox management was topical.
Markus, N., Hall, L. (2004) Foraging behaviour of the black flying-fox (Pteropus alecto) in the urban landscape of Brisbane, Queensland. Wildl. Res. 31, 345–355.
To track the foraging movements of Black Flying-foxes
Black flying-foxes around Brisbane were supplementing their diet with introduced or cultivated resources during a native food shortage, but this may have impacted the health of mothers and young. In general, food sources were exploited until flowering or fruiting ceased, and then bats sought out new foraging sites. The consistency of urban food supplies is highly likely to be a contributing factor to the increasing presence of flying-foxes in urban areas.
McClelland, K. (2009) Challenges and recovery actions for the widespread, threatened Grey-headed Flying-fox: A review from a New South Wales policy perspective. Ecol. Manag. Restor. 10, 110-116.
To provide an overview of how science is informing the management and conservation of the Grey-headed Flying-fox (Pteropus poliocephalus) in New South Wales.
The DECC continues to advocate full exclusion netting as the only reliable, non-lethal method for preventing flying-fox damage to commercial crops. The Greyheaded Flying-fox is an intelligent animal that quickly learns whether a potential threat is real or perceived. Negative public attitudes and conflict with humans remains a threat to the species, as identified in the NSW Scientific Committee’s final determination to list the species as Threatened.
McConkey, K. R., Drake, D. R. (2006) Flying foxes cease to function as seed dispersers long before they become rare. Ecology. 87, 271–276.
To determine if a nonlinear, threshold relationship exists between flying fox (Pteropus tonganus) abundance and their effectiveness as dispersers of large seeds.
The relationship between ecological function (seed dispersal) and flying fox abundance was nonlinear - for most trees in sites below a threshold abundance of flying foxes, flying foxes dispersed <1% of the seeds they handled. Above the threshold, dispersal away from trees increased to 58% as animal abundance approximately doubled. Hence, flying foxes may cease to be effective seed dispersers long before becoming rare.
Mcdonald-Madden, E., Schreiber, E. S. G., Forsyth, D. M., Choquenot, D., Clancy, T. F. (2005) Factors affecting Grey-headed Flying-fox (Pteropus poliocephalus: Pteropodidae) foraging in the Melbourne metropolitan area, Australia. Austral Ecol. 30, 600–608.
To examine the importance of six variables on the detection of foraging flying-foxes: (i) distance from the colony site ( (ii) distance from the Yarra River; (iii) the relative tree density of the municipality; (iv) whether the site was a park or street; (v) whether there was a relatively high or low density of trees at the site; and (vi) whether food was or was not detected at the site.
The probability of detecting a foraging flying-fox declined with increasing distance from the colony site, but increased with increasing tree cover, and was higher for parks compared with streets and when food was present. Flying-foxes were observed foraging in a number of plant genera that have no species that naturally occur in the Melbourne area.
Parris, K. M., Hazell, D. L. (2005) Biotic effects of climate change in urban environments: The case of the grey-headed flying-fox (Pteropus poliocephalus) in Melbourne, Australia. Biol. Conserv.. 124, 267–276.
To investigate: (a) whether Melbourne falls within the climatic range of camp sites of P. poliocephalus on the basis of long-term data; and (b) whether Melbourne has moved into the climatic range of the species as a result of urban development and human activities in the city
Temperatures in central Melbourne have been increasing since the 1950s, leading to warmer conditions and a reduction in the number of frosts. In addition, artificial watering of parks and gardens in the city may contribute the equivalent of 590 mm of extra rainfall per year. Hence, it appears that human activities have increased temperatures and effective precipitation in central Melbourne, creating a more suitable climate for camps of the grey-headed flying-fox.
Parry-Jones, K. A., Augee, M. L. (2001) Factors affecting the occupation of a colony site in Sydney,New South Wales by the Grey-headed Flying-fox Pteropuspoliocephalus (Pteropodidae). Austral Ecol. 26, 47–55.
To record the numbers of flying-foxes using the Gordon site over a 62 month period and report the results of the examination of droppings obtained at the site, in order to test for correlations between colony usage, diet and reproductive events.
The Gordon site was occupied by substantial numbers of flying-foxes throughout the entire period of 62 months from 1985 to 1990. As a result of the introduction of plants native to other parts of Australia and exotics from other continents, there is a variety of foods available throughout the year in the Sydney region, in comparison with less urbanized areas. This food supply permits the occupation of the Gordon colony site during winter and spring and reduces the migratory behaviour of flying-foxes throughout the year. The use of any food by flying-foxes from the Gordon site is probably linked to its attractiveness and availability, but not necessarily to its abundance, as even an abundant food supply may not be available to an animal.
Parry-Jones, K. A., Webster, K. N. (2016) Baseline levels of faecal glucocorticoid metabolites and indications of chronic stress in the vulnerable grey-headed flying-fox, Pteropus poliocephalus. Aust. Mammal.. 38, 195–203.
To determine whether the values obtained in assays vary in urban vs rural flying-foxes; to determine whether the levels of GCMs are related to the overall physical condition of animals; to develop a ‘remote’ method of testing the health of flying-foxes
Urban flying-foxes had lower Body Condition Indexes and elevated levels of glucocorticoid metabolites: 75% had levels that were higher than the rural range and 30% were higher by an order of magnitude. Such elevated levels of glucocorticoid (‘stress’) hormones are characteristic of chronic stress. While urbanisation can cause chronic stress, given the low BCIs observed, it is more likely that food shortage was the major stressor in this study. Significantly different results were found between male and female urban flying-foxes: males were in relatively better condition than females but had higher levels of faecal glucocorticoid metabolites.
Parsons, J. G., Cairns, A., Johnson, C. N., Robson, S. K. A., Shilton, L. A., Westcott, D. A. (2006) Dietary variation in spectacled flying foxes (Pteropus conspicillatus) of the Australian Wet Tropics. Aust. J. Zool. 54, 417.
To clarify the dietary habits of the Spectacled flying-fox, the level of dietary variation among camps and the extent to which P. conspicillatus is a rainforest specialist.
P. conspicillatus utilises a broad variety of plant resources from a variety of habitats. Seed and pulp from figs (Ficus spp., Moraceae) and pollen from the family Myrtaceae were most frequently represented in the faeces from a range of both wet sclerophyll and rainforest habitats. The dietary composition of P. conspicillatus at individual camps could not be predicted by the habitats located within a typical foraging distance of each camp (20 km), and although consistent dietary changes were seen across all camps over time, each camp had a unique dietary signature indicative of feeding on a distinct subset of available vegetation.
Parsons, J. G., Van Der Wal, J., Robson, S. K. A., Shilton, L. A. (2010) The implications of sympatry in the Spectacled and Grey Headed Flying-Fox, Pteropus conspicillatus and P. poliocephalus (Chiroptera: Pteropodidae). Acta Chiropterologica. 12, 301–309.
To investigate the climatic space of P. conspicillatus and P. poliocephalus from previously developed predictive models in light of evidence that the two previously allopatric species now co-oocur at Finch Hatton
The Finch Hatton location is climatically suitable to some degree for both P. conspicillatus and P. poliocephalus but the latter has a higher climatic suitability at this site. Historical records exist for P. poliocephalus close to this location but not for P. conspicillatus. The location of this mixed-species flying-fox camp is the most southerly distribution for P. conspicillatus, being 500 km further south than previous records.and its consequences
Plowright, R. K., Foley, P., Field, H. E., Dobson, A. P., Foley, J. E., Eby, P., Daszak, P. (2011) Urban habituation, ecological connectivity and epidemic dampening: the emergence of Hendra virus from flying foxes (Pteropus spp.). Proc. Biol. Sci. 278, 3703–12.
To explore a set of probable contributory mechanisms that explain the spatial and temporal pattern of HeV emergence; including urban habituation and decreased migration
Urban habituation increases the number of flying foxes in contact with human and domestic animal populations, and our models suggest that, in addition, decreased bat migratory behaviour could lead to a decline inpopulation immunity, giving rise to more intense outbreaks after local viral reintroduction. We also demonstrate that by incorporating waning maternal immunity into our models, the peak modelled prevalence coincides with the peak annual spill-over hazard for HeV.
Roberts, B. J., Catterall, C. P., Eby, P., Kanowski, J. (2012) Latitudinal range shifts in Australian flying-foxes: A re-evaluation. Austral Ecol. 37, 12–22.
To evaluate the robustness of previously published inferences concerning distributional shifts in Pteropus poliocephalus and Pteropus alecto, and the evidence that global warming has been a driver of these shifts.
The results do not support the hypothesis that either species range is shifting in a manner driven by climate change. Pteropus alecto expanded southward at about 100 km/decade, compared with the 10–26 km/decade rate of isotherm change. Neither climate change nor habitat change could provide simple explanations to explain P. alecto’s observed rapid range shift.
Roberts, B. J., Eby, P., Catterall, C. P., Kanowski, J., Bennett, G. (2011) The outcomes and costs of relocating flying-fox camps: Insights from the case of Maclean, Australia. Aust. Zool. 35, 277–287.
To examines the consequences of a coordinated, government-sponsored attempt to relocate a flying-fox camp in the township of Maclean, northern NSW.
The total cost of the Maclean relocation attempt was at least $400,000 including 640 person-hours of effort. Flying-foxes made 23 attempts in those years to return to the original camp, although the frequency of attempts declined over time. Twelve other sites were used during this time as temporary camps, including seven sites not previously occupied. In 2004, flying-foxes established a new continuously-occupied camp in the Iluka township, 16 km north east of Maclean. By comparison, In Melbourne, thousands of person-hours of effort and approximately $3 million were needed for the dispersal (including associated research and purchase of additional habitat). The benefits of the Melbourne relocation in reducing conflict with the general community and protecting heritage trees could perhaps be considered to outweigh the financial cost. However, these resources are beyond the means of most small rural and regional communities.
Roberts, B. J., Catterall, C. P., Eby, P., Kanowski, J. (2012) Long-distance and frequent movements of the flying-fox Pteropus poliocephalus: implications for management. PLoS One. 7, e42532.
To quantify the patterns of movement by P. poliocephalus among roost sites at a range of temporal and spatial scales.
Movement patterns varied greatly between individuals, with some travelling long distances. Five individuals travelled cumulative distances >1,000 km over the study period. Five individuals showed net displacements >300 km during one month, including one movement of 500 km within 48 hours. Seasonal movements were consistent with facultative latitudinal migration in part of the population. Flying-foxes shifted roost sites frequently: 64% of roost visits lasted <5 consecutive days, although some individuals remained at one roost for several months. Modal 2-day distances between consecutive roosts were 21–50 km (mean 45 km, range 3–166 km). Of 13 individuals tracked for >12 weeks, 10 moved >100 km in one or more weeks.
Shilton, L. A., Latch, P. J., McKeown, A., Pert, P., Westcott, D. A. (2008) Landscape-scale redistribution of a highly mobile threatened species, Pteropus conspicillatus (Chiroptera, Pteropodidae), in response to Tropical Cyclone Larry. Austral Ecol. 33, 549–561.
To compare the patterns of month-to-month camp-site use and P. conspicillatus population estimates over 23 months prior to Cyclone Larry, with the species’ use of camp-sites and documented population following the cyclone.
For 6 months after Cyclone Larry, up to 90% of the pre-cyclone P. conspicillatus population (ca. 250 000) was unaccounted for across the region, but after November 2006, the number of P. conspicillatus built up at located camp-sites until a post-cyclone peak of 209 000 at the end of the study in March 2007, comparable with the population estimates in March 2005 and 2006. There is no evidence that the cyclone caused significant direct mortality among P. conspicillatus, although there may yet be longer-term and indirect effects on population size.
Spencer, H., Palmer, C., Parry-Jones, K. (1991) Movements of Fruit-bats in eastern Australia, determined by using radio-tracking. Wildl. Res. 18, 463.
To determine the long-range movement patterns, if any, of the grey-headed fruit-bat (P. poliocephalus)
Bats moved between major colony sites for distances of up to 750 km; one bat from Lismore had a feeding range of 25 km, whereas in Sydney bats flew up to 17 km each night to feeding sites.
Tait, J., Perotto-Baldivieso, H. L., McKeown, A., Westcott, D. A. (2014) Are flying-foxes coming to town? Urbanisation of the spectacled flying-fox (Pteropus conspicillatus) in Australia. PLoS One. 9.Tidemann, C. R. (1999) Biology and management of the Grey-headed Flying-Fox, Pteropus poliocephalus. Acta Chiropterologica. 1, 151–164.
To examine the spatial and temporal patterns of association of spectacled flying-fox camps with urban areas in the main part of their Australian range.
Our results indicate that spectacled flying-foxes were more likely to roost near humans than might be expected by chance, that over the period of the study the proportion of the flying-foxes in urban-associated camps increased, as did the number of urban camps. Increased urbanisation of spectacled flying-foxes was not related to changes in landscape structure or to the encroachment of urban areas on camps. Overall, camps tended to be found in areas that were more fragmented, closer to human habitation and with more urban land cover than the surrounding landscape. This suggests that urbanisation is a behavioural response rather than driven by habitat loss.
Tidemann, C. R., Nelson, J. E. (2011) Life expectancy, causes of death and movements of the grey-headed flying-fox (Pteropus poliocephalus) inferred from banding. Acta Chiropterologica. 13, 419–429.
To generate information on demography and movements in large flying-foxes, information that is critical to management planning.
On average, hand-reared animals lived less than half as long as their wild counterparts (P < 0.001) and did not travel as far (P < 0.01). Major causes of death of 86 wild P. poliocephalus were: hyperthermia (33.7%);electrocution (18.6%); entanglement in fruit-tree netting (5.8%); entanglement in barbed wire (4.7%); unknown (32.6%). 77% of recoveries of wild-banded P. poliocephalus were within 20 km of where they were banded; the longest movement recorded was 978 km.
van der Ree, R., McDonnell, M. J., Temby, I., Nelson, J., Whittingham, E. (2006) The establishment and dynamics of a recently established urban camp of flying foxes (Pteropus poliocephalus) outside their geographic range. J. Zool. 268, 177–185.
To compile data on the size of the colony of P. poliocephalus in the Royal Botani Gardens Melbourne from 1987 to 2003 and answer three questions: (1) Did P. poliocephalus establish a permanently occupied camp in Melbourne as predicted by Aston (1987)? (2) If so, when did it become established and at what rate has it grown? (3) What is the seasonal fluctuation in numbers of individuals within the camp?
Regular monthly counts that began in December 1993 confirm the continuous presence of the species in Melbourne from that date onwards. The growth of the size of the colony from 1994 onwards was exponential, with a peak in March 2003 (when counting ceased) at between 20 000 (static count) and 30 000 (flyout count) individuals. The number of P. poliocephalus within the colony fluctuated across the year, with a peak in summer/autumn (December–May) and a trough in winter/spring (July–October).
Welbergen, J. A. (2011) Fit females and fat polygynous males: seasonal body mass changes in the grey-headed flying fox. Oecologia. 165, 629–37.
To investigate body mass changes in relation to reproductive behaviour in a large colony of grey-headed flying foxes (Pteropus poliocephalus)
Female body condition declined during the nursing period, but did not vary in relation to sexual activity. By contrast, males accumulated body reserves prior to the breeding season, but subsequently lost over 20% of their body mass on territory defence and courtship, and lost foraging opportunities as they also defended their day roost territories at night.
Welbergen, J. A., Klose, S. M., Markus, N., Eby, P. (2008) Climate change and the effects of temperature extremes on Australian flying-foxes. Proc. Biol. Sci. 275, 419–25.
To examine the effects of temperature extremes on behaviour and demography of vulnerable wild flying-foxes (Pteropus spp.)
A 2002 extreme heat even killed 3,500 individuals across nine mixed-species colonies. Druing this event a predictable sequence of thermoregulatory behaviours (wing-fanning, shade-seeking,panting and saliva-spreading, respectively) was witnessed and 5–6% of bats died from hyperthermia. Mortality was greater among the tropical black flying-fox, Pteropus alecto (10–13%) than the temperate grey-headed flying-fox, Pteropus poliocephalus (less than 1%), and young and adult females were more affected than adult males. Since 1994, over 30 000 flying-foxes (including at least 24 500 P. poliocephalus) were killed during 19 similar events. Although P. alecto was relatively less affected, it is currently expanding its range into the more variable temperature envelope of P. poliocephalus, which increases the likelihood of die-offs occurring in this species.
Williams, N. D. G., Mcdonnell, M. J., Phelan, G. K., Keim, L. D., Van der Ree, R. (2006) Range expansion due to urbanization: Increased food resources attract Grey-headed Flying-foxes (Pteropus poliocephalus) to Melbourne. Austral Ecol. 31, 190–198.
To quantify the food resources available to P. poliocephalus in Melbourne and describe changes in their diversity and temporal availability
Only 13 species recorded in the diet of P. poliocephalus occur naturally in the Melbourne area. An additional 87 species have been planted on Melbourne’s streets and there are at least 315 500 trees that are able to provide food for P. poliocephalus. Phenology records indicate that street trees have lengthened the temporal availability of food for P. poliocephalus. A period of natural food scarcity between May and August has been ameliorated by street trees which have provided nectar and a previously absent fruit resource. These changes are likely to be a major factor contributing to the recent range expansion of P. poliocephalus and the establishment of a permanent camp in Melbourne.