More Bats

 On the evening of 8 February we noticed a very large flyout of Grey-headed Flying Foxes from the camp at Mullet Creek.  This was against a very overcast sky.  Movement was well underway when we first saw them at 1930 hours and continued until at least 2000 hours when it got too dark to see them from home.  

On the 9th it was too hot during the day to get out and about so we decided to walk down to Mullet Creek to see the flyout. We got there about 1925 hours and although we could see a few bats flying around in the trees but none heading across the Lake.  A White-bellied Sea-Eagle passed by but didn't show any interest in attacking the bats.

A few Pacific Black Ducks were paddling around in the Lake.

At 1941 hours -  at least 10 minutes later than the previous night - a few bats seemed to be getting in the air.  The sky was much clearer this evening.  The initial photos were taken from a small jetty, about 100m towards Karbeethong Jetty, looking across towards the mouth of Mullet Creek.

By 19:42:38 a good number of bats were in the air.

This was 19:47:40 which I think was the densest flyout.

This photo was taken looking more up the track to the Adobe apartments: the street light is just visible in the bottom right.

We left at 18:55:18.  The numbers in the air had dropped somewhat but it was getting quite dark.  There were still plenty of bats in the trees along Lakeside Drive: I don't think these would be babies, expecting them to be in the middle of the camp rather than the edge.

A zoomed view of part of this group.

Looking back as we headed for home at 19:58:26.

Looking from home it is difficult to pick the direction of the flight path.  From out position at water level this was more obvious and varied as the event progressed.  

We were standing at the point marked as Karbeethong Jetty (wrongly, the Jetty is about 200m upstream, marked as on Google Earth as houseboat hire).  The camp is marked - very approximately - with green lines.  At the start of the flyout the bats were going in the yellow direction which would take them towards Harrison's Channel.  By the time of the 19:47 image this had swung round to the blue line heading for Howe Flat, and just before we left it had move further to the pink line towards Fairhaven.

Compared to other nights we have watched from here they seemed to be going quite high.  Frances saw a few dip into the water to cool off but rather less than on other occasions.

I rode down to Mullet Creek on the morning of the 10th and took the following snaps to give an idea of the density of the camp at present.  Not every tree was this full, but many were.  I didn't go right into the camp, as whatever they fed on last night did not share properties with Imodium (they must have found some fig trees).

On the evening of the 10th I watched from the school bus parking lot, which gave a rather different feel to the occasion.

The first few appeared at 1948.

The horde was underway by 1953.

After a very hot day rather more were taking a dip to cool down.

On the 13th and 14th the weather was cooler and overcast in the evening.  On the 14th heading along Lakeside Drive Frances noted that the bats were in trees between the bus stop and the gate to the East of Mullet Creek, indicating that the camp was still increasing in size.  Coming back home around 1700 hours we noticed these 'extra' bats still present.  On both dates the flyout started much earlier (~1910 hours) and stayed lower, heading towards Fairhaven rather than the Howe.  On the morning of the 15th (~0515 hours) there were bat calls coming from the Angophora grove close to our house.  By 0630 they had moved on - presumably back to the camp.

On the 16th the weather had been very pleasant with much less cloud than other recent days.  I first noticed bats flying out at around 19:28.  They were flying very high.  The photos to follow were all taken from home.

The numbers in flight grew considerably.  

I have counted the bats in this image, putting a coloured dot beside each bat, and changing colours for each 100.  My total count is 561 bats.  Earlier in the season I counted 155 bats in a similar image: on the same day a scientist from DEECA did a more rigorous count (and estimated from the area of the camp) coming to 25,000 bats.  Applying the ratio of my two photo counts gives 

(25000 * 561)/155 = 90,484

As I am fairly sure that there were more bats flying below tree line by this time which were not counted and, compared to the time of the scientific count, more bats flying out the back to the Miners Track area, I am happy to say there are conservatively around 90,000 bats in the colony.  At the time of the scientific estimate I did a shonky estimate based on how long it took a bat to cross the camera field of view and duration of flyout arriving at ~15,000 bats.  Using that as the base I arrive at a current estimate of 55,000 in the camp.

I have not attempted to measure the total size of the camp but compared to the size it was when counted scientifically there are many more bats visible along Lakeside Drive and the extent along that road is longer than I ever recall seeing in the past.

By 1945 hours - light fading fast - many more bats were flying low to the water but they were still going out in good numbers.

The flyout on the 17th was pretty standard.  My only image shows the eucalypt - presumably bloodwood (Corymbia gummifera) ....

.. on the far side of Bottom Lake.

The weather on the 18th was ordinary, verging on average.  By 1900 hours it was very drizzly and the bats didn't flyout until about 1925 by which time the light was very poor.

By 1948 it was close to dark, but the bats were still flying out.  Unusually quite a number of them were coming over our house and I tried to get a photo as they came near the moon, shining through the clouds.  Failed

On 20 March the wind was very strong from the SW and the sky somewhat overcast.  Flyout didn't start until 1925 and most of the bats were flying low towards Fairhaven.  A few - many less than the previous evenings - were going high and heading towards Dead Finish.

The situation on March 21 was interesting to say the least.  The sky was clear after a relatively cold day, but flyout didn't start until 1925.  Numbers also seemed low and the bats were initially at least all flying low, towards Fairhaven. By 1940 a few were flying higher, towards Dead Finish, but a higher than usual proportion seemed to turning back towards the Miners Track.

A quite large flyout close to darkness on both 24th and 25th.  On the morning of 26th the bats were very noisy in the Angophoras near home from about 0600 onwards.  There were also a lot flying past, going back to the camp.  That seemed to have ended by about 0645.

On 27th Frances walked to Bucklands and noticed that there were many bats close to - possibly on branches hanging over - Lakeside Drive. 

She also commented that at Karbeethong Jetty the bats could not be heard, but assisted by a SW wind they could be smelt.  (We have recently noticed a faint smell on Angophora Drive early in the morning.)

On 31 March from about 1917 hours, when Frances noticed the first flyout, the whole sky is full of bats. Some crossing the Lake but a much higher than usual proportion heading towards the town area. I think the camp is still full. (I didn't get out until close to 1930 hours when it was too dark to take photographs.) The other end of this was a very large fly in past our house on 1 April until about 0645: there are often a few fly past, stopping for a feed and a squabble in the Angophoras, but this was several thousands.

The flyout on the evening of 4 April was unbelievable: the biggest I have ever seen.  Starting about 1910 looking out from our deck the entire sky was full of bats flying in all directions.  It seemed that many were heading out across the Lake and then turning back.  Very unusually, a modest proportion were overflying our roof: they usually go across the Lake (with the precise path varying between Lakeside Drive and the Narrows according to how they feel) or basically up/above the gullies of Mullet and Two Mile Creeks.  Still going at 1930 by when it was too dark to see.

On 23 April a researcher from DEECA counted the camp.  He first measured the extent of the camp (6.23Ha) and then counted the flyout: although they started after twilight a full moon was providing light and he thought his count of bats going across the Lake was good.  His estimate was 66,000 bats: this is 8-13% of the Australian population of the species.

28 April comment on FB: Still a lotta bats in the camp. BIG fly out starting about 1745 hours: many of them going out low over the Inlet then turning back and higher and towards Genoa Rd/Miners Track etc. An inspection earlier in the day suggested camp about the same area but possibly slightly less dense. On the 29th the bats were calling as they flew back over our house from about 0530. When daylight arrived ~0600 a few were visible flying back.