I was visiting the St Kilda Botanical Gardens when a storm was approaching; the air felt electric. The sun disappeared behind dark, all-consuming clouds, and lightning could be seen cracking through the grey sky. My senses were heightened and from a nearby pond in the gardens I could hear the 'Creee... cree creee cree creee' of Southern Brown Tree Frogs calling. Then the rain started to fall, delicately splashing my face.
How do you experience, or sense a change in the weather?
These days, we are bombarded with weather updates, warnings and other information from our electronic devices, televisions, and even Siri and Google Home. In nature, animals and plants have evolved inbuilt systems to detect changes in the weather and react accordingly. For thousands of years, people have used some of these animals to predict changes in the weather.
By becoming more mindful and paying closer attention to nature, we can detect oncoming changes in the weather. There are several examples to draw on. Many insects hide away when a storm is brewing; black ants make themselves busy by covering up holes to their nests if rain is on the way; and there is even a saying, ‘when sheep gather in a huddle, tomorrow will have a puddle.’ One of the other well-known cues in nature is taken from frogs, as their evening choruses are generally a sign that rain is on the way.
When it comes to frogs, the events of reproduction must be synchronised with suitable conditions, so breeding can be successful. We can take advantage of this time and listen carefully to the unique calls of male frogs “wooing” the females to their pond. Many frog species breed seasonally, and are thought to use temperature, day length, moisture and atmospheric pressure (“weight of the air”) to time their breeding activity. The final trigger for most frogs is rainfall, as many species require free-standing water for fertilisation.
There are several local species in Melbourne that you may hear prior to a rainfall event. Here are a few examples to spark your interest.
The Southern Brown Tree Frog (Litoria ewingii) is a species that has adapted to urbanised habitats, and can be found from the city to the suburbs and beyond. The adults inhabit a variety of wet and flooded areas, and fortunately for us they are common in gardens and suburban areas. Southern Brown Tree Frogs can also be found calling long distances from water. The good news for us is they call all year round, and often in response to rain. So, next time you're out and you hear a series of rapid, whirring, pulsing notes, repeated 5 to 15 times – ‘creeeeeee creee creee cree cree cree’ (the first note is usually the longest) – it might be wise to grab a raincoat!
Another helpful frog is the Eastern Banjo Frog or Pobblebonk (Limnodynastes dumerilii). This species can call all year round, but has a peak in its calling period during spring and early summer. Keep your ear out for a short explosive note producing a resonant ‘bonk’. The call is usually repeated every few seconds. This fascinating species can migrate up to one kilometre to its breeding sites. It is also a burrowing species, commonly popping up in suburban gardens and sandpits where you may glimpse it foraging on the surface after rain.
Lastly, we come to frogs that alert us to the autumn rain Melbourne often experiences. One of the more common species you may come across is the Victorian Smooth Froglet (Geocrinia victoriana). I’ve recorded Victorian Smooth Froglets at Yarra Bend Park in Kew, and in the outer-eastern suburbs. The male frogs can be heard from low-lying areas within gullies, at the edge of wetlands and waterways (such as among moist leaf litter) that will flood after rain. They are a secretive species, and need an inquisitive ear to seek out their lovely and very distinctive call. Their song consists of a long, harsh first note, followed by a long series of short, rapidly repeated musical notes – ‘wa-a-a-a-a-ark pip-pip-pip-pip-pip-pip...’.
Not all frogs are “pond breeders”. The Victorian Smooth Froglet is an exception to the rule and is referred to as a terrestrial breeder for their curious and intriguing reproductive habit. Within a low-lying moist area, the male calls from a shallow burrow and the female will lay her eggs in the burrow on land, not in the water. Much of the development is done within the egg capsule. Once the rain floods their burrow, the tadpoles can emerge and complete their metamorphosis in free-standing water. Males will often call prior to or at the onset of a heavy rain event throughout March to May. The other not-so-common terrestrial breeders that call in autumn are the elusive Southern Toadlet (Pseudophyryne semimarmorata) and Bibron’s Toadlet (Pseudophryne bibronii); they have very similar double-note calls with an inflection on the second note – ‘ri-rick’.
So, next time you want to ask Siri what the weather will be like, perhaps take a walk outside in your local park and see if the frogs are calling. They may be telling you in their own lovely, melodic way to take an umbrella to work today.
You can investigate other pond-breeding frogs in Melbourne that may alert you to the onset of rain throughout the year. Take a look at frogs.org.au and the Melbourne Water Frog Census. You can also download the Melbourne Water Frog Census app or check out the recently launched Australia-wide Frog ID app. Both apps encourage citizens to record frog calls, so scientists can have a greater understanding of frogs around Australia and track their populations over time.
Christina Renowden has had an affinity for nature since she was a child. Over the years this love of nature has morphed into one role or another, including studying conservation ecology, researching urban frogs, and working as a consultant zoologist. She is now a mother of two and the founder of Leap into Nature. Since 2014, Leap into Nature has been creating and presenting a range of nature-based and environmental education programs for young people. Christina is excited to begin a Master of Environment in July 2018 at the University of Melbourne and is currently the Vice President on the committee of management for Environment Education Victoria.
Banner image courtesy of Rowan Mott.