Wing Tilting Habit of White Letter Hairstreaks

[Devon Dave]

Being fortunate enough to live near a site where the road level rises to a point at the upper Canopy height of a large Elm tree, I have been observing the behaviour of a small colony of White Letter Hairstreaks from a position not normally afforded to most.
From this vantage point characteristic habits can be studied throughout the day when the sun is out or it is at least warm if not overcast.
One thing that has intrigued me most is that most observed specimens have a noticeable habit of tilting their closed wings at an angle of 45 to almost 90 degrees to their body length whilst resting on leaves. Sometimes the closed wings are lying flat on the leaf a horizontal plane. They seem to do this regularly as a norm and my feelings are it is a signalling posture to either to attracted a possible mate as a courtship display , or warn off others that this is their territory.
But whatever the reason it is a trait I have not observed in other species to date, but I may be wrong and it is a common practice.
I have included some photos to demonstrate this wing tilt posture just for the records of those interested.

[jenks]

Hi Dave,
"One thing that has intrigued me most is that most observed specimens have a noticeable habit of tilting their closed wings at an angle of 45 to almost 90 degrees to their body length whilst resting on leaves. Sometimes the closed wings are lying flat on the leaf a horizontal plane. They seem to do this regularly as a norm and my feelings are it is a signalling posture to either to attracted a possible mate as a courtship display , or warn off others that this is their territory".

I`ve always assumed this angling is done to obtain the greatest amount of sun, and therefore heat, on their wings but maybe I`m wrong.

I saw 2 WLH spiralling and jousting above the canopy and another 1 sitting on a leaf in the canopy in the Elms at the Tongwynlais site shown in David M`s recent posting, on 9 July. Photographing not possible, cricked neck was the only result of my sighting.

Jenks.

[Devon Dave]

Hi Jenks ,
and thank you for your reply. You probably are correct its to capture the sun, but on some days I have observed this wing tilt it has been extremely overcast and also when the sun does come out it is not always a tilt in the direction of the sun. That's why I thought it may be a signalling motion. However it is of course just another interesting habit open for discussion. I will revisit the site over the next few days as we are forecast for a lot more sun and clear blue skies and try and note the direction of tilt in respect to the suns positioning more accurately. I will report my findings in a week or two.
Kindest regards,
Devon Dave.

[Pauline]

Hi Dave

I have photos of all the (British) Hairstreaks (except Brown) adopting this position and like Jenks my feeling is that it is connected to best posture for absorbtion of warmth. It seems to be something they do on a regular basis.Territorial displays and courtship have quite different body language.

[Devon Dave]

Many thanks indeed for that information Pauline, in which case I will drop my idea that this is a signalling gesture and go with the sun angle warmth related posture.
Congrats on your photographic achievements, I just need the Black Hairstreak now.
Dave.