To The Batcave!

Actually, more than one bat cave.  I was with a small group doing a bat survey.  You need a bat conservator's license for this, so I was lucky to be invited along.  This is one of a small group of caves at Combe Bank.  I am carefully not saying exactly where they are, and the GPS on the photos isn't accurate either, as there was no signal inside the caves.

I was not allowed to photograph the bats, even without a flash.  Apparently you need a license for that too .. but we did see several.  Some Natterer's, a Daubenton's and a Long-eared, tucked right into tiny crevices with just noses, wingtips and ears showing.  We also saw some cave spiders, which don't need a license ...

Cave Spider, perhaps Meta merianae, at Combe Bank on 24 February 2013.

I actually have some better record shots than this, but this one, taken by torchlight, is the most atmospheric.  And quite tricky to take, with torch in one hand and large camera in the other.

There was also a beetle, some mosquitos, some woodlice and lots of Ichneumon Wasps, probably Ambyletes species, but so far unidentified.

Unidentified Ichneumon Wasp at Combe Bank, 24 February 2013.

There are several similar species and this doesn't quite match any in my rather limited insect book.

There were several of these; they are the spiders' egg-cases, well wrapped in silk and hanging by a thread from the roof of the cave.

Cave spider egg sac.  Probably Meta merianae.  Combe Bank, 24 February 2013.

And this was just one site - though there are several small caves here.  It was a very interesting day!

Noctules and Moon

The moon and a Common Noctule over Warren Avenue Playing Fields.   1 July 2012.

On just a few nights each year. our largest bats come to Warren Avenue playing fields to feed on Summer Chafers.  Swifts love these chafers too, and swoop around the trees until quite late, but soon after sunset the bats take over as chafer-depleters.

The word came from Ishpi, our local bat expert, that the Noctules had been seen, and I went the same night with my camera and a long lens.  Last year I just had my bat detector and a tiny camera, and I photographed a chafer; this year I wanted some actual bat photos.

The moon was looking very photogenic when I arrived, so I took some shots.   That proved to be useful, as I was never able to get a decent shot of the moon and a bat together.  The top photo is a cheat, put together later with Photoshop, but it doesn't represent anything that wasn't actually happening.  Here's a more honest picture:

Common Noctule, Nyctalus noctula, flying over Warren Avenue Playing Fields.  1 July 2012.

That's the best I could get.  Those bats move fast, wheeling and darting, and it's not easy to keep up with them and work the controls at the same time.

Noctules at Shortlands

Summer chafer, Amphimallon solstitiale, with wings partly extended.
Warren Road playing fields, just after sunset on 14 June 2011.

Ishpi Blatchley, a local bat expert, let me know that noctule bats had been seen feeding in recreation grounds in Shortlands. This only happens at this time of year so I went out in the evening to see what was there.

I parked at an entrance to Beckenham Place Park where there were several open fields, and a stream, the river Ravensbourne. I also found a fenced-in playing field, and across from that an unfenced one, where I saw someone entering from the far side; it was Ishpi. Two other enthusiasts arrived not long after that.

The photo on the right is once again not a bat. It is one of the insects on which they were feeding. There were hundreds of these summer chafers swarming around poplar trees along the edge of an area of rough, but mown, grass, which from the remains of white line markings is used for cricket and football and perhaps other sports. Some of the chafers were on the ground, which is where we photographed this one. The flash makes it look a light brown; it was darker to the eye in the late evening light.

Only a few minutes after sunset I heard bat sounds on my detector and saw a noctule flying straight across the field. A few minutes after that, more appeared. Soon there were four of them flying at around treetop height, moving around the open area but mostly keeping near to the trees. Their sound on the detector was different from any of the other four bat species I have seen (common and soprano pipistrelles, Daubenton's, and serotines). There were loud, low clopping sounds and at the same time a series of higher chirps, all at about 20 khz. Most of the time it wasn't easy to distinguish the sounds made by individual bats. Sometimes one would swoop low, and occasionally one would fly just overhead, making it easy to see against the sky. They seemed to move faster and flap more often than the serotines I have seen recently.

Every now and then I heard one of them make a feeding buzz, a rapid series of clicks that echolocating bats use as they close in on their prey. Twice, I saw something small fall away from a bat after it made a buzz. Were the chafers getting away, or were the bats just biting off the juicy parts and discarding the rest? They were too far away to tell.

A chafer must be quite a substantial catch for a bat. It would probably be too big for one of the little pipistrelles — I saw one of those too — but the bigger noctules had no trouble. After about half an hour there was only one noctule left, so perhaps the others had had their fill, or they might have gone on to feed somewhere else.

Bats, Beetles, Bug

My bat-watching station, 1 June 2011.

This was another attempt to locate the roosting site for the Serotine bats that feed around Hayes. Again, there are no photos of bats. And again, we didn't find what we were after.

We met at the car park on West Wickham Common. I looked at the surrounding trees when I arrived, and found a late instar nymph of a forest bug, a type of shield bug. I'll post a photo when the adults appear. But on to bats. We spread out along Croydon Road and environs, and watched for Serotines.

I was halfway down a hill, with a good view of a clearing at the edge of the treeline, and a house we thought might be a candidate. But although Serotines were heard and seen, they did not seem to come from there. In fact they always seem to turn up first in the woods, which is very puzzling, as they are not known to roost in trees.

There was lots of wildlife. As it grew dark, moths and mosquito-like insects flew all around me. I recognised a white plume moth. One of the other sort bit me on the thumb .. and suddenly I saw something flying overhead. It was a big beetle, a cockchafer. I saw another later on.

This time I got a good view of some bats. A Serotine flew over my clearing and came back several times, swooping and catching insects, quite low and clearly visible against the sky. I also saw at least one Pipistrelle. I hope they were eating the creature that had just bitten me.

I watched the big bat flying around for about ten minutes. Some of the other also got a glimpse, but not such a good view. However, we are still no closer to working out where they came from.

Where Are The Serotines?

Part of my bat-watching zone.  13 May 2011.

Unlike my last bat post, this one has a photograph. Are there any bats in it? There are not.

Serotine bats have been seen in the neighbourhood of Hayes. They like to roost in old buildings, but no-one has found where these come from. Last night, a dozen people surrounded a large building in Hayes.

It seemed a likely candidate. They had been seen in the woods nearby, as well as other woods a mile or so away. Other likely buildings have already been checked out, with no results.

Organised by Ishpi Blatchley, a local bat expert, we started to assemble half an hour before sunset. Ishpi split us up to surround the building, and we watched, and listened on our detectors. I was covering the aspect of the building in the photograph. We saw no serotines. One of us saw a pipistrelle, which we weren't looking for.

Planes flew past a gibbous moon. Bats didn't. We waited until well after sunset, when any bats would definitely have flown out to eat. Our target building was eliminated as a serotine roost.

Serotines are twice as big as the common pipistrelles. My route back home took me through the wood behind the building. I heard pipistrelles as I walked along, and suddenly I saw two serotines flying and feeding along the edge of the trees. They were echolocating at 27 kiloherz, a loud popping call like a giant pipistrelle on my heterodyning detector. Another of the group joined me and we watched them cruising back and forth, snapping up insects, sometimes swooping just above our heads.

Where are they coming from? We could see houses nearby. Less likely, but that will be the next investigation.

Crackle and Pop

The thing about bat walks is that there are no photos. They take place after sunset, and torches and flashes are discouraged because they ruin peoples' night vision. But they are wonderful.

The walk on 16th April was in Kelsey Park, Beckenham. It was organised by the Friends of the park and led by Ishpi Blatchley, a local lichen and bat expert. The park is closed at night, so we were locked in for the duration of the walk.

Ishpi gave her usual talk about bats, their nature and habits, and we wandered around listening on heterodyning bat detectors for their supersonic echolocating calls. At first we heard the commonest British bats, common pipistrelles, and saw some against the sky flitting across clearings. When we came to an outlook over one of the lakes, we saw and heard a soprano pipistrelle, a little scarcer than common pips. Pipistrelles make a call that sounds like a fast series of hollow pops, very distinctive when you are familiar with it; at around 45 kilohertz for common pips, and 55 for the sopranos.

The real treat came when we approached the big lake. Not only was the air like bat soup, with pipistrelles flocking around the lake margin, but we heard one of the bigger bats, possibly a Leisler's or a Serotine. It was calling at about 27 khz, slower and louder than the pips. It circled around several times, but no-one got a reliable sighting. Ishpi recorded it and should be able to identify it later from an analysis of the recording.

This lake is a great place to see Daubenton's bats. These creatures are specialised to feed over water. They zoomed around the lake just above water level, and as they turned, followed by a guide's torch beam (strictly pointed away from us at low level) we could see their white bellies. They have big hairy feet with which they can catch insects, but they were too far away for us to see this detail.

Daubenton's bats call at about 40 kilohertz and make more of a crackling sound on the detector, almost sounding like radio interference with the pipistrelles, which of course were calling at the same time. Tuning into bat calls is very like tuning an old-fashioned long wave radio; they are both heterodyning devices.

Since first going on a bat walk last year I have become much more aware of their presence. And pipistrelles are easy to find. Last week I was standing on my balcony at night watching my cat wander around my tiny garden, and three of them flew less than two metres over my head; first one, then two more. Magic.

Geology at High Elms

Paul Rainey crumbling a piece of Seaford Chalk

Wherever I have lived, if there has been a garden the soil has seemed mostly to consist of clay. I had a vague image of the earth as consisting of rock, with clay on top. Even though I knew quite well that there were many other sorts of environment, in practice it always came back to clay.

Much of my current locality is chalk or gravel. How does this affect my current garden? Not at all, because the house was built on an old railway yard, and if I dig down a foot through the clay I find coke.

On Sunday there was a geology walk around High Elms Country Park and its immediate neighbourhood towards Farnborough, led by Paul Rainey of the Ravensbourne Geological Society. This area is almost all on chalk. You can see chalk very close to the surface; nearby, I have seen it turfed out of a badger's sett, and here it can be seen in road cuttings.

There is another way to see what is near the surface in woodlands in the south of England. All the woods have many trees that were toppled during the Great Storm of 1987, when winds of hurricane strength blew down an estimated 15 million trees. I got that number from Wikipedia, but I remember that night well. When those trees were pushed over, their root balls were tilted up and they brought with them all the attached soil. That soil is still mostly there and gives you a very good idea of what's under the topsoil, without having to dig.

Flint Lodge, the gatehouse to High Elms, showing flint in the walls

The top photo shows Paul Rainey crumbling a piece of chalk from one such root ball. Like all experts, Paul could read more from his surroundings than those less knowledgeable. Chalk, being a rock, albeit a weak one, can support more of a slope than clay or gravel. We were on Seaford chalk, and elsewhere on the estate is a layer of Lewes chalk, which is stronger and supports steeper slopes.

Chalk, of course, is full of flints. The Blackheath gravel layer of the nearby Hayes, Keston and West Wickham commons consists of small black flint pebbles, created where a sea has broken up larger flints and rolled them around. There were many such pebbles on the surface as we walked, which must have come downhill from elsewhere, as there is no gravel layer here.

Flints were a valuable resource in the stone age, and in more recent times they were used to surface walls, for protection or decoration. The area is full of houses and churches that demonstrate this. The second photo shows Flint Lodge, the gatehouse of the High Elms estate, which demonstrates this in name and in fact. The white border around the broken edges shows that these flints were freshly dig for this use. That border is usually weathered off on flints taken from the surface.

A chalk pit in High Elms Country Park

At the top of the slope is a playing field attached to Farnborough Village. Here, there is a layer of Thanet sand. Sand, chalk, flint, gravel .. it's easy to see that this whole area was once a sea-bed.

The various soils and rocks in this area have in the past been used as resources by the locals. The playing fields at Farnborough were once a sand pit. The gravel at Keston Common was a local resource. And here in High Elms Country Park is a chalk pit.

It goes down about 30 feet and branches out into three short excavations. This is where chalk was excavated to put on the fields, though just why the fields weren't already chalky enough I do not know. Chalk was taken from deep down because that nearer the surface was only good for paths and roads, not for the fields. This pit is now a home to bats; I wasn't able to find out what type.

(Added later: I have since heard from Ishpi Blatchey, a local bat expert, who wrote: "The ... dene hole .. is a bat hibernation site - not used in the summer as it is too cold for maternity roosts. Brown long eared, Daubenton's, and Natterer's bats are regularly seen there in winter by licensed bat workers who monitor the site for the National Bat Monitoring Programme." Here is a note of one of Ishpi's bat walks.)

As you can see, it rained during this walk ...

Here are some random images.

Cut ivy stems on a felled treetrunk near High Elms

Ivy can be quite substantial, and can be considered as a workable wood in itself.

Last Autumn's fallen leaves with signs of tar spot fungus

The edge of the field was full of leaves like this.

Weathered gate ball at The Clock House, High Elms

This was one of the decorative balls on the gateposts of The Clock House. I don't think it will last much longer. One good frost should split it apart. In fact, I can't see how it is still holding together.