Tuesday 26 March 2024

Couthness at Merumbula

 We went to Merimbula for a little retail therapy on 25 March.  After visiting a few temples of commerce we adjourned to the Red Rocks fishing jetty to look at the red rocks, eat our lunch, check for birds and see what was going on.

The red rocks were as usual very attractive.

Eating lunch was done, involving some pepperoni mini-pizza in my case.  There were few birds around apart from an immature Australasian Gannet which landed (?? not quite the best word) came down and sat on the water.
While looking at the Gannet a young fisherperson - who had been catching baitfish - got very excited , yelling "Dad, dad.  Gget the net.  I've got a Kingie."  He had indeed hooked a lovely big kingfish, rated by another member of the (small) crowd as above 65cm, and thus a keeper.  The net arrived and was lowered into the water.  Unfortunately the Kingie got under the jetty and broke off the line.

The young fisherperson must have then spotted some waterfowl which I didn't see, proclaiming "Duck, duck" rather loudly.




Thursday 21 March 2024

Sundry bird images

 This is a collection of more or less random bird photos I have taken recently.

A Restless Flycatcher turned up at home - in fact I think there were 3 in the area, judging by the churring calls I could hear.

Great Egret and Royal Spoonbill on the Broome St Lagoon.
A trip to the Airstrip fence was fairly quiet  but a pair of Scarlet Robins was pleasant.  Possibly indicating that Summer is finished.
A close-up on the male.
And the female.
Another member of the 'Robin' family: a Jacky Winter.
2 more Royal Spoonbills from the Lagoon.
A Little Egret from Coulls Inlet, beside the Shady Gully boardwalk.
An Azure Kingfisher at the small fishing jetty at the mouth of Coulls Inlet.


Tuesday 19 March 2024

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.






Tuesday 12 March 2024

Recent heat

You may have noticed it has been somewhat hot recently.  That had led to the BoM issuing a heat wave warning over various days for most of Victoria with the warning lingering in the Mallacoota area.  

I have compiled a blogpost defining various terms that can be used as shorthand for periods of extreme weather.

Here are the temperature readings from my weather station so far in March 2023 (note this is a screengrab image not a table).

The period 2 - 4 March is close to a cool spell, but fails as it is only 3 consecutive days, with an above average maximum on the 5th (after a significantly cold morning)!

From 6 to 11 March is a hot spell, as all readings for 6 consecutive days are above the daily average, albeit 3 readings are less than 1SD above the monthly average.  Embedded in that period is a heat wave from 9 to 11 March, with three consecutive days with both readings more than 1SD above the monthly average (bold red numbers).  (Looking at BoM forecasts I am confident that the hot spell will extend over 12 March with a fair possibility that the heat wave may also extend since Meteye implies a temperature <17.3C is possible up to midnight.) 

Indeed the minimum on the 12th was above the 1SD criterion, and the maximum above the +2SD limit so the heat wave continued for a 4th day (and the hot spell for a seventh  day).  I suspect the 13th will be a warm day, so will extend the hot spell but not the heat wave.

I have used a yellow fill with orange dots to indicate the readings that are >2SD above the monthly average.  The boundary value for that criterion for minimum is 20.3C so the 11th missed out on that by 0.4C.  Had we ended with 3 days with both readings >2SD above average I think I would have added a term of "extreme heat wave".

It should be stressed that my Weather Station compiles data on calendar days and as a result can give different results to BoM which is based on a reset at 0900 hours.  Thus my WS is currently showing a minimum for 12 March of 19.4C but that may change as a change comes through later in the day.  For BoM the current low temperature (18.5C) is likely to be preserved by the 0900 reset. 

I really wish the BoM would change to a calendar day, but appreciate this would cause much turmoil where stations are still based on manual readings, some of which have very very long series (eg Timbillica has a rainfall series starting in 1909!)  While only 2 of the 96 stations shown in Latest Weather Observations for Victoria are manual, the equivalent report for Queensland lists 14 manual stations. 


Heat waves and other extreme temperature phenomena

There seems to be a need for consistent terminology to cover extended periods of extreme temperatures in either directions.  This is most evident (in Australia) with periods of extreme heat leading to BoM issuing heat wave warnings.  However the same can apply to periods of very cold weather (noting that Australia's coldest recorded temperature - I think -22C - wouldn't cause people in Canada, Russia or most of the USA  to get their gloves out of the wardrobe, let alone put them on.)

High temperatures

The BoM definition, in their Glossary, of a heat wave is "A period of abnormally hot weather lasting several days. I have in the past seen - somewhere - this expressed more precisely as "3 consecutive days of both maximum and minimum temperatures significantly above the long term mean".  The closest I have been able to locate to this definition is in a document by the Climate Council:

"In Australia, a heatwave is defined operationally as a period of at least three days where the combined effect of high temperatures and excess heat is unusual within the local climate (BoM 2012; Nairn and Fawcett 2013). Two aspects of this definition are important. First, a heatwave is defined relative to the local climate. That is, a heatwave for Hobart will occur at lower temperatures than one for Alice Springs. Second, the concept of excess heat is also important. Excess heat occurs when unusually high overnight temperatures do not provide relief from the daytime heat."

 My operational definition of a heat wave has had the following elements":

  1. At least three days duration;
  2. The days should be consecutive
  3. Both minimum and maximum must be high;
  4. "significant" means greater than 1 standard deviation above the long-term term mean for the month.
I usually record daily extremes in a spreadsheet, in which I use colour codes to indicate the status of the minima and maxima.  The graphic below shows the situation for the period 0000hrs 14 Sept to 0900hrs on 19 Sept

Blue is below the daily mean for that extreme, orange is above the daily mean for that extreme.  Text in bold red is >1SD above monthly mean (not shown below, but bold yellow is >1SD below monthly mean).  The horizontal hatching means >2 SD above!  A code of 1 is a summarising indicator showing both measures above the daily mean.
So for the 6 day period concerned (and by 0900 on 19/9 the maximum is already 27.7 and thus >2SD above the monthly mean) we have 4 days which satisfy most of the criteria.  However days 3 and 5 only have 1 extreme more than 1SD above the monthly mean, so we do not three consecutive days meeting the other three criteria.  So it hasn't been a heat wave according to my rules.  

This seems a bit 'odd', especially noting that the maximum on 18/9 only missed being 'significantly high' by 0.3C.  It can be overcome by some semantics!  I will define another term "hot spell" to refer to:
  • a period of  consecutive days in which both minimum and maximum temperature are above the average temperature for the day, and 
  • a majority of the days  are more than 1 SD  above the long term monthly average, which allows for a few readings to be 'warm' rather than 'hot'; and
  • the period lasts at least 4 days (chosen to make it a little tougher than a 3 day run).
Going back to mid September 2023 here is another clip, showing final results.  The readings with horizontal black lines indicate reading >2SD above the long term mean.
There is not a heat wave  in this period as a few readings fail the 'significance' criterion.  However the period from 14 to 20 September is 7 days with both readings above the daily averages and 11/14 (79%)  readings more than 1 SD above the monthly average.  This counts as a 7 day hot spell.

I will also define a hot day as a day in which both extremes are more than 1 SD above the long term monthly average (for example 25 September).  This would allow the definition of a heat wave to become "3 or more consecutive hot days" but I am happy to stick with the more wordy definition which spells out the elements.  

I will also for completeness define: 
  • a warm day as a day with both readings above the daily average but one or both by less than 1SD;  and 
  • a warm spell as a period of at least 4 consecutive days with both readings above the daily averages but less than half more than 1 SD above.
Note that a heat wave can be embedded within a hot spell (or even a warm spell).  For example, in the example above, if the minimum on 16/9 had been 11.4C that would have given a 4 day heat wave within the 7 day hot spell.

Low temperatures

These are the equivalents to the periods above but going low rather than high.  In the second table image above both results for 23 September are filled blue (below daily average) with yellow text indicating >1SD below the monthly average.  As it's both readings, that is a cold day.
  • Cool day: both readings < daily average;
  • Cold day: both readings more than 1SD below the monthly average.
  • Cool spell: at least 4 consecutive days with both readings <daily average, and <50% of readings more than 1SD below the monthly average.
  • Cold spell: at least 4 consecutive days with both readings <daily average, and >50% of readings more than 1SD below the monthly average.
  • Cold snap: At least 3 consecutive days with both readings more than 1SD below the monthly average




A trip to Eden

 We had to take the Mazda to Kings Smash Repairs in Eden as a result of my efforts.  A pretty pleasant drive although there was lots of smoke haze from Habitat Reduction Burns.

The smoke was evident at the lookout over the Bay so we decided not to do a walk there, but to go to Cocora Beach and try the walk to Quarantine Bay.  At the beach the pontoon was well endowed with a range of species of Cormorants.
The holey rock was looking photogenic.
As the walk emerged on to Quarantine Bay Road we came across a boat trailer graveyard.
There were several people cleaning fish and throwing scraps - in some cases quite large items to the team of cormorants, pelicans and stingrays below the tables.  This guy was hand-feeding a very large stingray - I suspect an Eagle Ray.  However, experts on iNaturalist have identified them as Bathytoshia brevicaudata Smooth Stingray (also known as Short-tailed Stingray).

There were 2 rays present.
4 Sooty Oystercatchers watched on!
In a few centuries people will be mining this breakwater for Pelican and Cormorant guano!
At times the competition for food got a little vigorous.

Sometime the eyes hold more than the gullet!
So you have to retreat to shred your meal in peace.
The walk back was a bit of a slog going up 47m to a ridge line!