Forest pollinators: the grey headed flying fox (Pteropus poliocephalus)
With Melbourne’s warmer weather fast approaching, a unique little Australian mammal fills the night sky with a quirky array of sound and colour. The grey headed flying fox is a megabat only found along the East coast of Australia. Sporting a distinctive grey head and orange-brown collar the grey headed flying fox is a keystone species to our forests and is our only long distance pollinator, flying up to 50km in one night, and maintaining the biodiversity and health of forest ecosystems. Victoria’s largest colony of grey headed flying foxes is located at the Yarra Bend reserve in Kew where up to 30,000 bats roost in trees along the Yarra River. Unfortunately despite having large, seemingly stable populations, Melbourne’s grey headed flying foxes are faced by a couple of major threats. With rising temperatures and increasing urban growth, this species which once numbered in their millions are facing massive population declines with as few as 400,000 grey headed flying foxes remaining in the wild.
Humans and flying foxes share a similar preference for where to establish their homes. Because of this, increasing human populations and expanding urban sprawl have impeded greatly on the habitat of grey headed flying foxes, pushing their colonies to relocate each time their homes are destroyed. Prior to the 1980s we had very few flying foxes in Melbourne because the winter climate was too cold for the bats to remain year round, but by 1986 warmer temperatures and a significant increase in the number of feed trees available to these pollen and nectar loving creatures allowed the first colony of flying foxes to establish in the heart of Melbourne. By 2003 the population of grey headed flying foxes in Melbourne had quickly grown from only 15 bats to over 30,000 individuals.
Unfortunately with bats living so close to us and in such large numbers, there’s often a lot of conflict between humans and bats. Flying foxes are frugivores and as such they feed on the fruits of many trees grown by landowners and farmers. For this reason many people hold a negative perception of flying foxes without understanding just how important these creatures are in maintaining the health and biodiversity of our gum forests. Most times humans and urbanisation pose one of the biggest threats to our flying foxes with shooting still legal in certain areas, powerlines causing electrocution, and entanglement from fruit tree netting being just a few of the dangers our bats are faced with.
The other key threatening process that our bats face is global warming. With temperatures rising at an unprecedented rate each year, our flying foxes are acting as the ‘canaries in the coalmine’ of the climate crisis. Unlike humans, flying foxes lack the ability to sweat, and with temperatures rising so rapidly they haven’t had time to adapt. For the grey headed flying fox temperatures over 42 degrees are considered days of extreme heat where these creatures suffer from severe heat stress and are often seen dropping from the trees out of exhaustion. Global warming is one of the biggest drivers of population declines of our already vulnerable flying fox colonies.
Maintaining flying fox colonies is extremely important, as without these animals we would be without the financial or physical means to do the sheer volume of work that these bats perform every night, at no cost, to conserve our forest ecosystems. Luckily for these creatures there are many organisations dedicated to ensuring their survival such as the Australian Bat Society and the Australian Research Centre for Urban Ecology who perform monthly bat counts to monitor the success of Melbourne’s Yarra Bend population. The next megabat count is on the 8th of October, and the group are always looking for volunteers to help out. To get involved you can contact the counts organiser Rod on 0412 562 429.
Author: Sarah Beebe.
Nodding Greenhood (Pterostylis nutans)
It’s September and the weather is finally warming up! Many plant and animal species come out of their winter dormancy at this time of year. Road traffic will soon be held up by hoards of ducklings, possum joeys will start falling out of trees, and everyone will need to dust off the old anti-magpie helmet. However, one species will go about its springtime business largely unnoticed. Nodding Greenhoods (Pterostylis nutans) are flowering right now, all over Victoria.
Nodding Greenhoods, also known as Parrot’s Beak Orchids, are a relatively small orchid that grows up to 30cm high, with flowers up to 25mm long. Each plant bears a single flower, which are easy to overlook as they are green and translucent. Their name refers to the way the flower droops over, causing it to look like a hooded figure (or a parrot’s beak). At the base of the flower stem is a rosette of three to six oval leaves.
Nodding Greenhoods are found throughout most of Victoria, excluding only the dry north-western corner of the state. In regards to Melbourne, this species once inhabited much of the eastern and southern parts of the city, and today can be found in numerous parks and reserves. Nodding Greenhoods can be found throughout the Dandenong Ranges, south to Frankston and surrounds, and as far west as the CBD. Most recently I found them at Baluk Willam Nature Conservation Reserve - an absolute must-see for anyone who is interested in Australian orchids. This reserve is home to 73 orchid species - that’s over one third of Victoria’s orchids all in the one spot! Nodding Greenhoods are locally common, forming large colonies on moist, sheltered sites in a wide range of woodland and open forest habitats.
Nodding Greenhoods are able to reproduce both sexually and asexually. This means that they produce seeds, but also form clonal colonies. This species has a long flowering season, some plants flowering as early as May, others as late as December. The flowers of Nodding Greenhoods are not at all spectacular or eye-catching. Instead, this species attracts its pollinators (namely male fungus gnats) by exuding a scent that mimics the pheromones released by their pollinators’ female counterparts. The male fungus gnat lands on the touch-sensitive labellum (a modified petal), which catapults and temporarily traps the gnat against the column (an organ that both distributes and collects pollen). As the gnat struggles free, it picks up and deposits some pollen, escapes the flower, and then moves on to the next orchid. This is sexual deception as its best - Greenhoods do not produce nectar, so the gnat does all the work of pollinating the Nodding Greenhoods, but alas receives no reward.
As this species exists in relatively dry, nutrient-poor habitats, it has evolved a few mechanisms to help it survive. All Greenhoods are deciduous, meaning that for much of the year they exist as tubers in the soil, avoiding the hot and dry periods that occur over much of Summer and Autumn. Another mechanism that assists in water conservation is the rosette of leaves at the base of the flower, which helps to funnel rain towards the centre of the plant. The water then falls between the leaves at the centre of the rosette to the ground, and is absorbed by the plants roots. In order to combat nutrient-deficiency, Nodding Greenhoods have evolved a mycorrhizal relationship with fungi in the soil. This allows the orchid to exchange photosynthesised organic matter with the fungi in return for inorganic nutrients that the fungus is able to extract from the soil.
This hardy little orchid is inconspicuous and quite boring when you first look at it, but it has a pretty interesting lifestyle. If you find yourself out in the forest anytime soon, make sure to look down. There may be a Nodding Greenhood at your feet - but hopefully not under them!
Author: Emma Walsh