Scotch Argus and Sun

[Jack Harrison]

It has been the received wisdom for donkey’s years that Scotch Argus doesn’t fly unless it is sunny. The might have originated with South (1905) or Ford (1945) but has repeated ever since. This is not my experience so I decided to do some tests to day.

I recently bought a light meter (not a photographic model) that measures levels in Lux
Tacklife LM01 for £10
https://www.amazon.co.uk/Tacklife-LM01- ... 911&sr=1-8

Nobody would claim that this is a precision instrument but it is reasonable to make comparisons in different situations.

Scotch Argus is widespread and abundant in this area. I went to my guaranteed spot just three miles away.
In that small clearing, I counted as many as 15 in view at a time. Males going over but plenty of new females.

The sky looked like this – cloud and sun - perfect for my observations.

Not actually where I did my survey but even so there were Scotch Argus in the foreground grass.

Data (no discernible difference behaviour male and female)

Full bright sun = 125,000 Lux (for the scientists, equates to about 1,000 watts per square metre)

125,000 to 45,000 lux butterflies active even though at 45,000 sun obscured enough to prevent shadows

45,000 to 33,000 basking wings open

30,000 lux and below no activity as they simply vanished even where previously noted basking.

When full sun returned, no activity for about a minute then full activity.

I would be the last t clam that this is a very rigorous investigation but it gives some pointers.

A similar study of other species would be worthwhile. In particular, I am intersected in Guy Padfield’s lux reading in the clear sunny skies of mid-winter Switzerland when the temperatures are scarcely above zero. Light level might be in some instances more important that actual temperature.

I presume you are now all going to buy ten quid light meters.

Jack

[Tony Moore]

I presume you are now all going to buy ten quid light meters.

Nah! I just usually look at the sky...

Tony M.

[Jack Harrison]

Thanks for such a constructive input.

jack

[CallumMac]

Interesting stuff Jack. I hadn't heard that about Scotch Argus before. My own experience of this species, from visits to the Speyside region, the Pitlochry area, and the west Highlands sites around Oban, is that it will fly in decent numbers without sunshine, so long as the air is sufficiently warm (I reckon 16-17 degC is just about enough) and/or humid. Perhaps in much of Scotland it takes a bit of sunshine to get the temperature up to these levels? The thing that really seems to get them hunkered down is either a cooling breeze or a cooling rain shower that drops the temperature below 16. However, when the sun does come out, it quickly becomes clear that the numbers that were flying in the "warm/humid but overcast" conditions are but a fraction of the true numbers present.

Incidentally, the same seems to be true of Speckled Woods in the historic Oban population, and to a lesser extent some of the other species I've seen there (Peacocks, Green-veined Whites). I've recorded large numbers of SWs at Shian Wood in conditions which it would not be worth getting out of bed for, if at a site in the English population! To me that suggests local adaptation in west Scottish populations to allow flight in sub-optimal conditions, presumably because there is no guarantee that there will be a nice sunny day during the short life-span of a butterfly. There is plenty more evidence that the Oban population is totally unique. They happily fly - and display territorial behaviour - in open damp meadows; they will nectar at ground level on heather(!); and when brought back to the lab, they roost at the base of their flight cages (perching on the side, about 1 inch from the floor), unlike individuals from every other population which roost on the ceiling of the cage (INCLUDING the Speyside population, which to me casts significant doubt on their origin!).

[Katrina]

Very interesting Jack and CallumMac.
On my very limited experience of one holiday to Speyside I would agree that they don’t fly in cool breeze.

[Jack Harrison]

I have been running a Davis weather station for some years
You can see it here (the humidity and dewpoint sensors are faulty so ignore those)
https://www.wunderground.com/personal-w ... UNITEDK534

On days when there is sun and rapidly passing clouds, the temperature hardly changes when the sun goes in. Equally, it doesn’t rise rapidly when the sun reappears. So my observations about the behaviour of Scotch Argus (and I am sure the same applies to other species) suggest that solar radiation is much more important than trivial changes in temperature (wings in effect solar panels).

It is well known that flighty species like Orange Tips are devils to photograph when there is continual sun. My technique (when younger and more agile) was to observe where the butterfly landed as a passing cloud approached. I would home in on it and then when the sun came out again, there was about 30 seconds of photo opportunity as it responded to the brighter conditions. There were even a few precious seconds when it opened its wings before flying off again.

I can't comment about the effect of wind on fly/no fly. Although Scotch Argus is widespread here, I tend to observe in sheltered habitats (such as in top photo above). Very little wind here at the moment, but when windy, will look observe in another of my morr open hotspots, Findhorn Valley. However, I'm going away on Monday for three days and the Scotch Argus season will be almost over by the time I get back

Jack

[David M]

Interesting findings, Jack. I wonder whether the same is true for Mountain Ringlet?

[Tony Moore]

I wonder whether the same is true for Mountain Ringlet?

A couple of years ago I spent a morning at Irton Fell. It was warm (19/20/C) with very light cloud cover and, despite fairly vigorous searching, there was not an MR to be seen. At about 1. pm, the cloud lifted and the sun shone. Within ten minutes you couldn't move for MRs - dozens in the air at once. It clouded over again at about 2 pm and they vanished...

Tony M.

[David M]

Thanks, Tony. Seems epiphron is more dependent on sunshine than aethiops.

[MikeOxon]

This is not my experience so I decided to do some tests to day.

As a retired physicist, I applaud your desire to collect experimental data. I was pleased to note that you also considered the effects of other factors, such as air temperature.

I feel that it is interesting that two of our most successful groups of butterflies use different 'strategies' to make use of solar radiation. The 'Browns' have dark wings, which presumably are good absorbers of energy from the sun, whereas the 'Whites' have wings that are remarkably efficient solar reflectors. It appears that Whites use their wings to reflect the radiation onto the body, where the all-important flight muscles are located. There must be interesting research studies that could be carried out on these processes. I know that the wings of Whites have already been studied as a possible means for improving the efficiency of solar panels - ref: https://www.nature.com/articles/srep12267

As a sideline, your results show just how much solar energy reaches the earth's surface. My wife uses one of those light meters, similar to yours, to measure light levels in the greenhouse, and I have used it to measure light levels in our living rooms under artificial (LED) lighting. In our kitchen, which has 'bright' daylight-white lighting, the light levels are around 180 lux (lumens per sq. metre) - compare that with sunlight! - and yet the room seems 'bright' Our LED reading-lights achieve a similar intensity on our books. There's a useful article about 'sunlight' on Wikipedia, which points out that the light level from solar radiation as far out as the orbit of Pluto is comparable to what we have in our living rooms!

Mike

[Jack Harrison]

I'm currently watching England hammer India at cricket. (Is it PC to refer to India as an inferior team?)
Umpire checked light lever with a meter - it seemed to the same £9.97 model (made in China!) that I recently purchased and used for my Scotch Argus investigation.

Jack

[David M]

Enjoyed the cricket myself, Jack.

Are they really using the same light meters?

[Jack Harrison]

It (at the cricket) certainly appeared to be the same meter but of course can't be sure although I did replay a few times to check.

I am going off this morning to the west coast to complete the missing (for me) section of the North Coast 500

If the weather forecasts are correct (rain, cloud, dull - dreich) my light readings might be negative

PS. Looking better this Monday morning but wet tomorrow

Jack

[David M]

I am going off this morning to the west coast to complete the missing (for me) section of the North Coast 500NC500.jpgIf the weather forecasts are correct (rain, cloud, dull - dreich) my light readings might be negative

Good luck with that, Jack.

Any chance of a few panoramics along the way?

[Jack Harrison]

I am back from that outing. No panoramas as it was (as expected) Dreich with a capital D. Pictures taken inside cloud aren't very interesting.

Didn't see a single butterfly although a few dragonflies (large and unidentified). Nice flocks of Ravens but the highlight (low light) was midges by the million. Stepping out of the car was quite a challenge.

The scenery is (presumably) spectacular. I will go again but not sure the best time of year. One road sign said "Normally impassable in winter". April might be optimum when if nothing else, fewer cars on the single track roads.

I wonder if there is anyone left in Germany at the moment? Germans seem to have taken over West Scotland. But the influx gave some entertainment. At the table next to me in the B & B were two German bikers. For breakfast, they were offered Fried Egg, Poached Egg, Scrambled Egg, Boiled Egg (soft or hard), Omelette, Bacon, Tomatoes, Mushrooms, Sausages, Black Pudding..... The only word they seemed to understand was 'Sausage' so the poor chaps had to have sausages whether they liked them or not. Good job there wasn't the option of round sausages, square sausages, Lorne sausages otherwise they would still be there.

The previous day there was a different German family. The lady managed to send her Orange Juice flying over the table. "Oh mein Gott".
She was not amused but husband thought it as funny as I did.

Jack

[Jack Harrison]

A brief moment of brightness at Loch Maree.

Lots of these youngsters.

Jack