Saturday, 30 January 2016

The bats of Karbeethong

In my posts about our recent trip to Mallacoota I mentioned the colony of Grey-headed Fruit Bats a few times.  Some close-up photos are in the later parts of an earlier post, while my best images of the flock in flight are here.  I thought it might be interesting to record what we observed, based around some images snipped from Google Earth.

This first images shows the 'suburb' of Karbeethong - about 5 km along the Inlet from the town of Mallacoota, with the green dot giving the position of the bat colony.
There are two clues to the existence of the colony shown below.  The first is the calls of the bats as they communicate with each other.  These are clearly audible to humans within the yellow lines.  That is what first alerted us to the existence of the colony.  A second clue is the sharp aroma of bat guano which can be detected by my crummy honker within the brown lines.
When we first observed them, in early 2015, we saw them from the house, streaming out in the evening basically as shown by the black arrows
That was also the story in the most recent sightings.  They seemed to emerge as dusk settled, for the first few evenings at about 2035.  It seemed to take about 10 minutes for the colony to empty out.

On our last evening it was very overcast and thus getting dark somewhat earlier.  The bats were swarming by 2010.  However, rather than heading straight out up or across the Inlet, for several minutes they appeared to circle as if unsure what to do.
At this stage the airspace was pretty crowded.  This led to quite a few of bats clipping the power lines as they circled (and the utility company has put hangers on the lines to enables flying beasties a chance of seeing them).  This was revealed more by 'tings' coming from tensioning devices close to the poles than actually seeing a strike.

By about 2025 things seemed to have settled down and, while some were still circling, others were flying off.  As I had gone down the hill to get some photos I was able to notice that as well as the torrent heading NNW there was also a good number heading SSW.
 This suggests to me that there were two feeding areas more or less as shown here.
I presume that there were a lot of Angophora floribunda flowering in those areas as I am advised that is a popular food resource for the bats.

A final comment is to note that Tammy is not at all happy to go anywhere near the colony.  Whether it is:
  • the noise - I can imagine she'd pick up a lot of the high-frequency echolocation calls as well as those audible to humans; or 
  • the smell - she mainly hunts by nose so is presumably pretty sensitive in the stink department;
which she doesn't like isn't clear.

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