On November 7, 2015, the Sydney chapter of the Society for Conservation Biology graciously hosted Dr. John Martin, wildlife officer at the heritage-listed Royal Botanic Gardens and Domain Trust and Centennial Parklands. Reflecting his deep-rooted passion for working in the field, Dr. Martin guided the captivated audience on a trek through the swamps of the Centennial Parklands, stopping periodically to discuss key findings of his ongoing work in the conservation of the Gray-headed Flying-fox (Pteropus policephalus), and Black Flying-fox (Pteropus alecto).
Despite being listed as vulnerable on the IUCN Red List of Threatened Species, the Gray-headed Flying-fox is considered to be a pest in parts of the New South Wales region. Playing an unequivocal role in long distance pollination and seed dispersal, the predominantly nectarivorous species tends to aggregate in large numbers, systematically defoliating the canopy of the trees they roost in through agitation of the branches. While certain regions, such as the Melaleuca dominated swamplands of the Centennial Parklands, have evolved to cope with this disturbance, many of the trees found in the Botanic Gardens do not share this protection and fall victim to the megabat populations. Realizing the potential for loss of both a historically and scientifically significant Australian landmark, Dr. Martin was faced with the daunting task of relocating 30 000 Grey-headed Flying-foxes to a more suitable habitat.
The Royal Botanic Gardens and Domain Trust have played host to Grey-headed Flying-fox populations long before it was set aside for conservation. As Dr. Martin put it, the species does not have one particular roosting site but rather multiple temporary roosting sites, or “motels,” of which they cycle between regularly. It is estimated that there exists over 100 of these motels in the New South Wales region alone, with each varying in the number of flying foxes at any given time due to seasonal and temporal variation. Loss of these roosting sites due to human driven changes in land use has caused flying-fox numbers to soar at remaining sites, while increases in food availability in urban regions has led many of these straggling populations to cluster in the city center.
To wildlife ecologists like Dr. Martin, relocating the bats is only half the battle. In order to tag and relocate flying foxes, the team must first set up mist nets in areas frequented by the colony. As incoming bats get caught in the traps, they lower the nets and attach radio tags to their thumbs before releasing them back into the wild. This ensures that researchers can study the dynamics of the colony both before and after their dispersal. Through a herculean combination of tagging and solar-powered satellite tracking, scientists at the Royal Botanic Gardens closely monitor the movement of the populations to their new sites.
Careful deliberation with the New South Wales Office of Environment and Heritage, in concordance with the Commonwealth Government, led to the usage of percussive noises as a means of flying fox relocation. Over an arduous 18 months, Dr. Martin and his team coasted along the garden paths in the waking hours of each day in an attempt to dissuade flying foxes returning from their nightly feast from taking residence. Armed with only a modified golf cart and a mix-tape of various screeches, industrial noises, and heavy metal, the scientists hoped their intrusion would be enough. One-by-one, the bats ceased to roost in the region until one morning the whole population had seemingly disappeared.
Unfortunately, citizens living in Sydney’s suburbs were not as impressed by the feat. Calls began coming in as homeowners were being woken up in the dead of night to the sounds of flying foxes loudly fornicating in the trees surrounding their land.
It turned out that the animals had moved into fig trees in numerous home gardens in the Sydney region. As a result of their reliance on wasps, fig trees produce flowers and fruit throughout the year capitalizing on the demographic variability of its pollinator. Conversely, this meant that the bats had a continuous, yearlong, food source, creating the ideal location for roosting habitat. Pressured by state and local governments and compounded by the tragic death of a young boy bitten by an ailing flying fox, the researchers were once again faced with the task of relocating Sydney’s Grey-headed Flying-fox population.
With the colony roosting directly overhead, Dr. Martin took this time to dispel the myths regarding the contraction of life-threatening diseases from flying foxes. According to the Queensland Department of Environment and Heritage Protection, the two most pressing diseases that carry the potential to affect human health are the Hendra virus and the Australian Bat Lyssavirus. Both diseases are spread through salivary transfer from a diseased individual, either directly or through an equine intermediate host. While effects on bat health are poorly understood, Dr. Martin stressed that the chances of contracting either of these diseases is virtually nil following proper training and handling procedures. This includes not handling any visibly sick or injured bats without sufficient training, and taking adequate precautionary measures to prevent the spread of the disease.
Illness and negative human interactions are not the only threats to the survival of the flying fox. The severe heatwave that passed through much of Eastern Australia in early 2014 left over 45 000 flying foxes dead in a single day with an overwhelming 96% being Black Flying-foxes. Dr. Martin explained that this species is especially vulnerable to high temperatures as they are unable to tolerate the same extremes as their counterparts, the Grey-headed and Little Red Flying-foxes (Pteropus scapulatus).
As the earth’s climate changes and extreme heatwaves become an ever-present reality, only time will reveal how the New South Wales flying fox population will respond. With scientists projecting one of the hottest summers to date, researchers such as Dr. Martin, in conjunction with educated citizen scientists, will play a key role in determining the fate of one of Australia’s defining species in both the coming months, and the coming years.
Find out more about New South Wales flying foxes and get involved!