Purple Emperors on Oak Sap

Emperors and Empresses feed, almost addictively, on small sugar-rich bleeds from distressed veteran oaks, especially during the second half of the flight season and in challenging weather conditions. 

Heslop called favoured trees 'Feeder Trees'. Here's a good one, from Knepp (the left-hand tree) -

The features are usually small whiteish bubbles of discharge, like this -

 Rot hole discharge, like this, are also favoured, but are much rarer -

Big runs of 'black treacle' from wounded trees are exceptionally rare, and dry up quickly. Many formed after the great storms of 1987 and 1990, after trunks twisted and broke in strong winds. Oozes from Noctule bat roosts are also good. 

Hornets, Red Admirals and Commas also visit these sap bleeds, along with a host of flies (hoverflies in particular). Watch for Hornet and Red Ad activity under the oak canopy, and watch them home in on the sap bleed. An Emperor or Empress may well be about...

However, feeding on sap runs is a high risk strategy, as Hornets readily predate Emperors. This is what happened to a large Empress at Knepp, 14/7/23 - 

This is a modern problem. I lived in East Hampshire from the mid-70s into the early 90s, and never saw a Hornet - not even in the long hot summer of 1976: they were common in and around the New Forest only. They colonised Alice Holt Forest during the mid-1990s. Likewise, they were absent from the landscape around Knepp until the mid-90s. 

Also, Heslop (lead author of Notes & Views of the Purple Emperor, published 60 years ago) doesn't mention Hornets at all, despite working the Bentley Wood area (SE Wilts, close to the New Forest) and knowing the butterfly's fondness of oak sap.

Here's a Hornet on a sap bleed -

Here's a photo of happier moments, from 14/7/23 -

Wind and Rain...

The jet stream has jumped south and is running right over the Empire, bringing wind, cloud and rain. Curse and crush it! This is an old-fashioned July...

On Wednesday, I managed to see a male in my local wood back home in Glos, then two males sparring at what is at present the only known reliable male territory in the county (near Daneway Banks, of large blue fame).

Back at Knepp on Thursday, in variable weather, I managed to see 58 Purple Emperors including 15 females. They were desperate to get going, and made the most of any sunny break. 

They were also very hungry and were sapping like mad, like these two females - 

and this torn female - 

They were getting pushed off the sap bleeds by Red Ads and Hornets. A good way to spot sap bleeds is to watch for Red Ads flying under the oak canopy, and Hornets.  The Red Ad is making a big stab at winning Butterfly of the Year...

I managed to cobble together the PE transect, for Week 4 of the season. This totalled 30, but I would have got >36 had the weather allowed. 30 is excellent for Week 4.

They are ageing fast. No good specimens were seen, though some of the females were in reasonable condition. 

The gale forecast for Saturday 15th (St Swithun's Day...) is likely to reduce Emperor numbers considerably. My guess is that the season at Knepp will end around July 25th, though it may persist a little longer at some of the 'later' sites.  

Males have stopped coming down to feed on the rides, nationally, and are now stopping flying during the mornings. 

Finally, great to hear Knepp's Purple Emperor safaris being lauded by Martha Kearney on Radio 4's Today programme this morning (6.55, 14th July). Knepp's been running them for ten glorious years... 

 

News from the North

Whereas the Purple Emperor has emerged in surprisingly good numbers down south, it seems to be having rather a shocker in the northern parts of its realm, and also in much of East of England region. It's hard to tell as smaller populations are difficult to monitor - away from central southern England, many populations are close to or below what IRP Heslop usefully termed our 'observation threshold'.

Confession: this is almost the opposite of what I thought would happen! I predicted, on this Blog, reduced numbers in the Southeast region, due to the impact of last summer's drought on sallows, eggs and young larvae, but a good year in the western and northern reaches of the Empire where there was a bit more rain last summer.

The Empire's western fringes seem fine; e.g. good numbers in Savernake Forest, despite the loss of rideside sallows. 

There also seems to be considerable disparity in the timing of the flight season. The season may only just be getting going in Notts - although the populations there may also have crashed. The first male was seen in Sherwood Forest only on Sunday July 9th, a pristine male.

Nationally, we are having a long spell of poor weather right now - cloud and wind associated with a slow-moving area of low pressure, making this an old-fashioned July. Canopy-dwelling butterflies are very hard to work in windy conditions, even when the sun appears. 

By the time the weather improves, it may be too late for many smaller populations...  Hang on in there and use whatever sunshine we get well...

Doings: Sun July 9th

Rather too windy over much of the Empire. Yet another day for leeward edges, only.

Great to see a photo on Facebook of a pristine female taken at the London Wetland centre at Barnes on July 7th. I visited the Centre in 2017 and felt it was suitable then. 

This butterfly is Everywhere, albeit in low numbers: Look (up, leeward) and Thou Shalt Find...  

A good count in Savernake Forest by Dave Law: 15 sightings along Three Oak Hills Drive including two groundings (suggesting it's still relatively early in the flight season there - Sav's a 'late' site), with six males active in the Dead Beech Glade (halfway up 3OHD on the E side, a much better site than The Column where everyone goes...).  

I saw five at a new site on the edge of Swindon-where-the-shadows-lie, then retired home to watch the glorious end of the Headingley Test Match...

We're still getting rather mixed messages from Fermyn Woods, Northants, with many visitors being rather disappointed. Odd that no aberrations have been reported from there, in a midsummer in which a few 'Black Admirals' and aberrant Silver-washed Fritillaries are being seen, plus a nice aberrant Comma in the West Midlands yesterday.  

In fact, numbers seem rather disappointing north of the Thames generally, with the exception of the Oxfordshire / Bernwood area.  

Low pressure is forecast for this week, which will make things difficult.

Finally, I'm pleasantly surprised by how few sallows died in last summers heatwaves and drought. Here's one from outside Knepp's main area -

 

Sat July 8th

A cloudy - but, at last, calm - day, punctuated by a hour's worth of thundery rain around midday. It was supposed to clear up nicely from 2pm, but glimmered and glowered instead. Emperors were nicely active during the glimmers.

At Knepp, the Purple Emperor season is starting to age, as testified by this old boy, struggling to feed amongst the wet grasses, albeit  after doubtless playing a prominent role in the Partygate scandal -  

He'd been to visit the ecology students' compost loos - 

But I was shown a photo of a near-pristine male, who'd probably emerged there yesterday, saw a couple of freshly emerged females, and the males are still avidly searching the sallow stands for females. All this indicates that the Knepp season is far from ending - they'll be good for a couple of weeks BUT DON'T VISIT KNEPP AFTER JULY 23rd, they'll be over - and they've stopped feeding from the track surfaces.  

I'm heading back to Glos and Wilts for a few days.

Doings: Fri July 7th

 Knepp. Neil counted 141 there yesterday, finishing at 7.30pm after a good evening flight, including 18 females - 7 of them involved in tumbledown rejection flights with males, and serial violence against Bullfinch, Great Splatted Woodpecker, Wood Pigeon, Chiffchaff and assorted titmice.

I was there too, but didn't do so well and saw virtually no violence. Males were assiduously searching the sallow fields for females during the morning, which suggests that females are still emerging there. They will stop doing this very soon though, and start taking the mornings off. Be warned. And the males have already stopped descending to feed on the tracks. 

Neil and I both walked the Knepp PE transect, 15 mins apart. He and his brother totalled 52 (the third highest count on record, and best after 2018) - but with two counting; I totalled only 43 (one counter) but under-recorded towards the end, as they suddenly conked out in the heat at 3pm.

A lot of feeding on sap runs. Look out for aggregations around veteran oaks, then spot Red Ads and Hornets visiting the small sap bleeds. At one sap run, we had three females perched close by, plus at least two males in the air close by - all had been booted off the sap bleeds by Hornets.

I've no idea what goes on in the mind of the Empress - 

Elsewhere, Rev John Woolmer saw only 8 in 4 hours in the main Fermyn Woods block, 9.30-2pm, and met others who had had similar experiences. His conclusion is that the FC's felling of rideside sallows has adversely impacted on the PE, but maybe the season is more advanced there than we think and the males are stopping descending to the rides? However, Fiona Barclay fared much better, counting 12 in 45 mins.

Great that Ian Surnam turned up PE at Coleorton Hall near Ashby de la Zouch in Leics. This is where Coleridge & Wordsworth had their spectacular bust up...

Nationally, the butterfly is now AT PEAK, and seems to be having a very good year nearly everywhere - the exception seems to be the East of England area and much of the region north of the Thames. 

Sighting at Southrey Wood

Had an enjoyable hour or so in the company of Richard Smyth at Southrey Wood today, which is part of the Bardney Limewoods National Nature Reserve, located in central Lincolnshire. This is a wood that I have searched and searched and searched for Purple Emperor on many previous occasions, not only this year, but in the preceding two years as well. All prior attempts to find Purple Emperor there have been fruitless, but today we recorded one male, which was low down, only a foot off of the ground, probing a Small-leaved Lime Tilia cordata tree, which was covered in a sticky residue.

The photo shows that the butterfly is extremely fresh, but the left hindwing has curled up on the inner edge near to the body.

My thanks to Richard for making it a very memorable day!