How animals survive the baking Bunuru (summer) heat, which is becoming increasingly harsher each year, never ceases to amaze me. Humans rely on staying cool at the pool, beach or inside with the air-conditioner on, but our wildlife has evolved a variety of strategies to cope with the harsh conditions. Often the trick to keeping alive involves going underground.
Above is an image I took earlier this year of a wetland that I have been revegetating for over 10 years. As you can see here - it's not very wet! However, recent Djeran rains (which have signalled an unusually 'good' start to this El Niño year), have begun to moisten the soil of Perth Hills creeks, and even allowed some wetlands (including the one above) to begin filling up. The liquid messages have reached our subterranean residents and informed them about the new season of life emerging up top. While checking the water levels of my dam over the past few days, and delighting at how fresh and clean the water is, I've noticed one particularly beautiful animal emerging from beneath the softened clay and becoming active: Booyi, the Noongar word for the Oblong Turtle (Chelodina colliei).
Being so close to the water made me notice a cloudy section between the cracks, where something had disturbed the mud, and I then spotted a second turtle! This one was still mostly buried beneath a large lump of clay, with only the shape of one side of its shell being visible.
|An active Booyi swims past one that is still well buried beneath the mud (shown by the arrow).|
Looking to the opposite bank I then spotted a third turtle attempting to hide between cracks in the mud. As you can see below, this turtle was a little less camouflaged than the previous one: its red-brown stain tells us this individual has come from deep beneath a part of the dam with different coloured mud.
The turtle eventually disappeared deeper, and I noticed it had apparently excavated a small cavity beneath the cracked lump of clay (to its left in the above photo). Oblong Turtles are known to aestivate (go into a state of metabolic 'dormancy') during summer months, and I considered this might even be where this turtle had spent the long summer, when the dam was dry. And after the first rains, perhaps these muddy underwater 'caves' are suitable daytime hiding places while the dam's water is very shallow, and not covering the rocks, logs and reed beds which will offer protection once the water level rises?
I began searching the dam more thoroughly and spotted one more Booyi. This individual was in a very unusual position, hiding on its side in a large crack in the clay, a very well-concealed spot. Before I moved closer to photograph it, I noticed the turtle's eye was closed (or maybe both - I could only see one!), a possible indicator the animal was brumating (a term used to describe dormant behaviour triggered by cold temperatures, the 'opposite' to aestivating).
The water might have initially brought them out, but with only small patches of low autumn sun hitting the water, these solar-powered animals swim a fine line between stop and go!
It's not only adult turtles that find refuge below ground. You can read more about how the young of this species start their lives in this news post. In the meantime, I will observe the movements of the adult Booyi to see if they remain present in the shallow, clear water, and if their activity increases when the dam fills up and the daily temperatures increase. An interest in natural history means there is no such thing as boredom!