Right place, right time - Daubies in the moonlight

Despite owning all sorts of camera equipment, it's a given that, whenever I see something I'd really like to capture, I don't have any of them to hand. Happily the latest iphone has solved that for me. I must be honest - I bought the very latest model just as it came out, only because I needed a new phone anyway - trend-setter I ain't!

So there I was, in one of those "wow, look at that" moments and for once I had the means to capture it in my pocket. A group of around 10 Daubenton's Bats, hunting over a moonlit lake in Northumberland last week, showing their prowess at grabbing prey from the water's surface. 

Beautiful and impressive.

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The return of "one-ear"

Each winter I regularly don my hard hat, waterproofs, torches etc and deliberately choose to descend into dark, wet, muddy and essentially unpleasant places. Hardly the act of a sane adult, but then nobody's ever accused me of being one of them! Surveying underground bat hibernacula (places used by hibernating bats) provides survey data for the National Bat Monitoring Programme (NBMP), creating useful information about bat population change. I am also undertaking a long-term study of how bats vary their use of underground sites through the hibernation period.

One site I visit regularly is a tunnel in the Dumfries and Galloway hills (See "A Most Peculiar Hibernaculum", 28 February 2009). Built several hundred years ago to channel a water supply for a small village, one end is now blocked and the open entrance is less than one square metre. Inside the tunnel opens up to a sufficient height to walk upright and continues through the solid rock for 350 metres (not quite the 500m I said in 2009, but I've measured it now!).

The entrance to the tunnel - about a metre across.

 

Four years ago I was carrying out a survey in the tunnel and found a Daubentons Bat (Myotis daubentonii) that was a bit different from the others: it only had one ear. The other appeared to have been torn off. Perhaps the ear had been lost in a predator attack, or maybe the ear had been caught on a thorn in flight. Whatever the cause, most of the ear was missing, though the tragus (the inner part of the ear appeared to be intact). 

Even more interesting was the fact that this bat was carrying a ring. Unlike birds, which are ringed wholesale, bats are only rarely ringed. This is because it isn't possible to ring bats round the leg in the same ways as birds: their tail membrane extend all the way to the ankles. Instead, bat rings are actually horseshoe-shaped and fit loosely over the forearm. The are difficult to fit and the chances of the bat being later injured by the ring is greater than for birds. For this reason bats are only rung as part of specific research projects, with clearly-defined aims. 

"One-ear" - you can see the ring on her left forearm and her missing right ear.

 

So One-ear's ring number was an important piece of information, but the number extends around the forearm, making it impossible to read without disturbing the bat. I decided to leave the bat and returned four weeks later, fervently hoping it was still there (I didn't want to return more quickly, to minimise disturbance to other bats). This time I was equipped with scales and measuring calipers, so that I could measure the bat's weight and forearm length and make an informed decision as to whether, having been disturbed, it was likely to have sufficient fat reserves to complete hibernation safely (A bat carer was standing by, in case it wasn't). Happily One-ear turned out to be a female and have plenty of fat reserves to see her through the winter.

Armed with the ring number I was able to discover something of her history. She had been rung at a summer maternity roost the previous August by Sue Swift and Iain Mackie of Aberdeen University, as part of a research programme. The roost was 35km away in a straight line, but given the hilly nature of the area it's more likely she had followed valleys to the tunnel, making the journey closer to 45km.

Since then she has turned up in the tunnel as regularly as clockwork every January. Whilst it's nice to see her (and she's starting to feel like and old friend) she is also a useful source of information. Normally I can't identify individual bats within the tunnel but One-ear can be easily identified, allowing me to track some of her decisions about where to hibernate within the tunnel.

Whilst I have seen bats with all sorts of injuries, One-ear is the only one-eared bat I have encountered...until last year, when another bat turned up in the tunnel with a very similar injury, but without a ring. So when I carried out the January NBMP survey this year I had my fingers crossed and I'm happy to report that not only was "One-ear" there again, so was "Lugless"!

It's interesting to conjecture the effect that having a missing outer ear might have on an echolocating bat. It is easy to assume that, with only one fully functional ear  a bat might be unable to gain a three-dimensional image of it's surroundings. The outer part of the ear acts in a similar way to a satellite dish, reflecting sounds into the ear and normally a bat can move the ear to channel sounds from varying directions. However the survival of One-ear and now Lugless shows that they are able to make allowances for this disability and carry on navigating and hunting successfully.

Remember it is a criminal offence  in the UK and Europe to disturb roosting bats without an appropriate license. Bats in hibernation are especially vulnerable. Please don't go poking about underground, looking for bats unless you have been properly trained to do so. Not only are you running the risk of prosecution (quite rightly), your actions may be harmful to bats and underground sites can be very dangerous for the uninitiated. If you'd like to get involved join your local bat group and learn how to do it properly (and legally). 

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A Bat in the Hand....

...takes a great deal of work to achieve!

In company with a small group of people from Lothians and Scottish Borders bat groups I attempted to try out my new harp trap last night (see "The Kitchen Table Harp Trap", under February 2008).

The site was a ruined castle, set in a secluded valley in the Scottish Borders. "Ruin" is probably the wrong word, as the seventeenth century noble who set about building it never completed the job but, with massive stone walls up to 50 feet high, it really looks the part. Barrel-vaulted cellars with plenty of deep gaps and cracks in the stonework provide good roosting opportunities for bats. There are woods and a river close at hand, providing foraging opportunities for several bat speices and in the past we have trapped Natterer's Bats (Plecotus nattereri), Daubenton's (Myotis daubentonii) and Brown Long-eareds (Plecotus auritus).

Trapping bats is enjoyable, but there needs to be a valid scientific reason to interrupt the bats in their normal activity. On this occasion bats were to be rung as part of a long-running study of bats using sites of this type in the Scottish Borders. In addition, I was planning to remove parasite specimens as part of my studies into their distribution and host associations.

Two harp traps were put in place: mine and a slightly larger one, each covering the entrance to one of the cellars. There is an art to siting a harp trap: it needs to cover as much of the entrance as possible and gaps need to be filled as far as possible, to prevent bats flying round the trap. A tarpaulin, some leafy twigs and an old coat were pressed into service around my trap:

It was quite cold, dipping as low as 5 degrees centigrade after sunset and bat activity wasn't high, apart from the large numbers of Soprano Pipistrelles (Pipistrellus pygmaeus) dispersing from their roost in a nearby farmhouse. Nonetheless, we caught four male Daubenton's, all of which emerged from one of the cellars. Frustratingly, it wasn't the cellar which had my trap at the entrance!

Two of the bats were recaptures and had been rung on previous visits to the site, but the other two were new and, as well as being weighed and having their forearm length measured, each had a tiny numbered aluminium ring slid onto it's forearm.

None of the bats had many parasites. This is often the case in spring, especially with adult males, which usually carry a lower parasite burden than females and juveniles. They are able to move between roosts to avoid parasite accumulation, whereas the females and juveniles are together in the maternity roost for several weeks each year, often with many other bats. I like to think that juvenile bats may also have similar personal hygiene issues to many human teenagers!

The picture above shows the fouth bat to be caught, who caught my interest as he had a tromiculid mite larva in his ear. The Trombiculidae are a large family of mites, including members of the genus Leptotrombidia, which parasitise bats for part of their life-cycle. Their larvae hatch within a bat roost, climb onto a bat and attach themselves, often in the bat's ear or on the forearm. There they take a meal, before dropping off the bat to become predators of other small arthropods within the roost during their nymph and adult phases.

I was particularly interested, as there are very few records of these parasites on British bats, partly because records of any bat parasites are rare and partially because they can be difficult to remove. Fortunately, this bat was quite placid and, with Carol-Ann (the "bat whisperer") holding him, I was able to paint the mite with a little isopropyl alcohol using a very fine brush, to make it release it's grip, and then remove it with fine soft forceps.

Once home I checked and have been unable to find any records of a trombiculid mite on a Daubenton's bat in the UK (unless anyone reading this knows better?), although that doesn't necessarily make it a rare species: probably just an under-recorded one. It will probably be a while before I am able to positively identify it to species: there are no field guides!

I haven't mounted the mite yet, but here's a rough and ready picture taken at x120. The larvae are usually a distinctive orange colour when seen on a bat. With their mouthparts buried in the bat, they look like tiny orange jelly beans.

As for the harp trap, it is still waiting to be christened with it's first bat. Watch this space...

Please note, trapping and handling bats without proper equipment, training and experience can be very harmful. Furthermore, in the UK it is illegal to do so without appropriate licences from Scottish Natural Heritage, Natural England, the Countryside Council for Wales or the Environment and Hritage Service in Northern Ireland.

If you're interested in getting involved in working with bats, the best starting point is your local bat group: http://www.bats.org.uk/bat_group.php

A checklist of mites found on British bats can be downloaded here: http://www.nhm.ac.uk/hosted_sites/acarology/saas/saasp/2003/saasp14.pdf

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Is spring springing yet?

When does Spring start? According to the Met Office, spring starts on 1 March, although the traditional start is the vernal equinox, on the night of 21/22 March. Here we are in mid April, so surely spring has started?

From a wildlife point of view, spring activity starts when the prevailing weather conditions permit, so in truth it's quite a variable thing, not just in terms of date, but geographically. The south of England is likely to experience signs of spring one or two weeks before they appear here in Scotland.

With some members of Lothians Bat Group, I went to Edinburgh's Blackford Pond after sunset, one evening last week. If you live in Edinburgh this is a great place to see large numbers of Daubenton's Bats (Myotis daubentonii) and Soprano Pipistrelles (Pipistrellus pygmaeus) in the summer, and the group usually run a bat walk there every year. On this occasion we wanted to see if there were the first signs of bats emerging from hibernation yet.

With an ambient temperature after sunset of just 2.5 degrees celsius, it was questionable whether we'd see any bats at all, but what was probably a lone Soprano Pipistrelle passed by a couple of times and we watched one, and later two Daubenton's Bats feeding on the pond. There was very little food for them, so they were having to range over the whole of this large pond, to find enough flying insects to eat (they looked to be small Sedge Flies). With such a low temperature, it's possible that these few bats were some of last year's juveniles, desperate for food after the long months of hibernation.

So is it spring? Well, not really from a bat point of view, as it seems like the main population are still in hibernation. The graph below shows the night-time temperatures at the Gogarmor meteorological station, to the west of Edinburgh, since the start of April. As you can see, there was a brief peak of warmer temperatures at the start of the month, but it has been quite cold at night since then.

Having said that, there are other signs of spring. As we walked around Blackford Pond, we had to tread carefully to avoid a large number of toads, commuting towards the pond, in order to mate?

Since then I have also seen some discarded eggshell from what must be a very optimistic bird and last weekend, I watched a group of Brown Hares (Lepus europaeus), boxing and chasing each other: the so-called "mad march hare" behaviour, associated with the onset of the breeding season. This behaviour actually continues through to September, but is far more noticeable just now, whilst the grass is short.

Hopefully we'll get a spell of warmer weather soon, and we'll start to see more bat activity, as the adults move out of their hibernation sites and the move towards maternity roosts commences, ready for the breeding season around June. My bat detectors are charged up and ready...

My website: plecotus.co.uk