What's in a city?

In modern Britain we live in a man-made landscape. Whether you look at stone walls and sheep folds on a remote hillside in Sutherland, a leafy farmscape in Devon or a built-up part of south east England, man's handiwork is there to be seen, profoundly affecting the habitats available to our wildlife and of course, our bats.

I have always found it interesting to place wildlife within the landscape: where do they live? Where do they forage or hunt? How do they move through the landscape? Where are they present or absent? Where are they threatened by predators and where do they take refuge?

We are fortunate in the 21st century to have easy access to satellite photography free of charge, via websites such as Google Earth and Bing Maps, which allow us to explore this swiftly and with a nice glass of Merlot to hand!

I thought it might be interesting to look at a random square kilometre of a major city and see what habitats useful to bats would be apparent, using one of these websites.

Here is my square kilometre. Two things instantly spring out: this is very obviously a built up area, but there are clearly green places here. Are they just amenity grassland, or more structural habitats which might they offer hunting places for bats. And are they connected, allowing bats to move through the city?

Zooming in makes some of these habitats more apparent. Here, the classic suburban wildlife habitat displays it's strength. These gardens may be individually small, but together they form a block of habitat, with trees and shrubs providing potentially good foraging habitat for generalist species, such as Common Pipistrelle (Pipistrellus pipistrellus) and Soprano Pipistrelle (Pipistrellus pygmaeus). In the south Soprano's tend to have a riparian affinity, but here in Scotland they are more numerous than the Commons and tend to use a wide variety of edge and suburban habitats.

Also in my square kilometre is another classic urban wildlife habitat: a cemetary. I recently carried out some bat surveys close to a large cemetery in East Kilbride and was delighted by the number of Foxes which emerged from it each night, to keep my survey team company. On one memorable evening two of us watched a young Fox edge up to within a few feet, grab a plastic bottle and run to a safe distance with it. Apparently unimpressed it then urinated on the bottle and stalked off!

This cemetery appears to enclose a lot of mature trees. These are likely to harbour plenty of insect prey for bats, especially if some of them are native species. Non-natives tend to be home to generalist invertebrates, but native species are also likely to offer a home to many more native invert species, for whom the tree provides more specialist niches.

Also in the square kilometre is what appears to be a public park, probably offering similar foraging habitat for bats (though not necessarily undisturbed conditions to allow Foxes to successfully breed!) So with a cemetery, a public park and plenty of mature gardens our city bats seem to be quite well-provided with foraging habitat. There are also plenty of houses and industrial buildings which seem likely to provide the potential for roosting Pips and some of the more mature trees could include holes and crevices for roosting bats too. The next question is how do the bats move between all the features? What commuting corridors are available to them?

Often lined with trees and shrubs, urban railways offer excellent wildlife corridors and this square kilometre has several. Here two cross each other and elsewhere a disused railway line has been developed into a cycleway. I'm sorry to revert to a foxy, rather than batty theme, but I was travelling on a train in Ealing which stopped at signals. Right outside the carriage window a vixen relaxed in the sun, whilst her three cubs played, completely unperturbed by the proximity of a trainload of disgruntled commuters!

Even better, within this square kilometre is the mother load: a stretch of canal. With trees, shrubs and hedges providing security for commuting bats and foraging opportunities for Soprano Pips, this is an excellent wildlife corridor. Emergent and submerged vegetation provides homes for plenty of invertebrate prey for Daubenton's Bats (Myotis daubentonii) and the smooth water is perfect for them to hunt over. Smooth water helps echolocating Daubies to pick up emergent insects on or just above the surface.

Canals without vegetation are not necessarily poor foraging places. A few years ago I surveyed the Union Canal with a team of volunteers, attempting to map foraging sites. To my surprise, the most active foraging sites were the ones with little or no vegetation, rather than those with plenty of vegetation and diverse prey species. These concrete-lined canal sections had large numbers of Chironomid midges hatching. They are amongst the first species to occupy stagnant water and the bats demonstrated that, as far as they were concerned, quantity trumped diversity!

The next time you encounter a bat, try using this method to look at the surrounding habitat. You may be surprised how much you can conclude about likely hunting locations, commuting routes and possible roost sites which the bats may use.

My website: http://www.plecotus.co.uk/

The Great Hibernaculum Hunt Revisited

A couple of times recently I've described the hibernaculum survey work I've been doing, together with several other members of Lothians Bat Group. We've been looking at potential hibernacula and sites with historical winter records of bats, in the hope of adding to our list of active hibernation sites.

The goal of all this work is to ensure that hibernacula - the most vulnerable of all bat roosts - are protected and also to to contribute as much data as possible each year to the National Bat Monitoring Programme.

(Carol Ann demonstrates how some sites are just plain awkward to access)

Having reached a stage when I've arrived at the bottom of my list of possible sites, when we're running out of winter and when frankly I've seen enough wet, muddy and claustrophobic underground places to last a lifetime, I thought it would be interesting to take stock.

Including surveys of exisiting hibernacula, both in the Lothians and in Dumfries and Galloway, in the past three months I have surveyed:

• 6 limestone mines
• 1 copper mine
• 7 lime kilns (one of them flooded to about half an inch higher than my waders!)
• 2 tunnels
• 4 castles
• 2 soutterains
• 1 WW2 underground bunker
• 2 pill-boxes
• 3 air-raid shelters

Out of all those sites, the following records were made:

• 16 Natterer's Bats (Myotis nattereri)
• 5 Daubenton's Bats (Myotis daubentonii)
• 1 Unidentified myotis bat (Myotis sp.)
• 6 Brown Long-eared Bats (Plecotus auritus)
• 16 Pipistrelles (Pipistrellus sp.)

(Two Natterer's Bats hibernating in a cave roof crevice )

The frustration is that all the bats were in the sites where we expected to find them. In other words: no, we haven't found any new hibernacula! That said, there are several sites which have strong potential and will be revisited next year. The disappointing result is probably only to be expected. Bats are extremely discerning about sites they use for hibernation: their requirements regarding temperature, humidity, constancy of both and lack of disturbance are very precise. That is exactly why it is so important to find and protect these sites.

(A Daubenton's Bat hibernating in a gap within the wall of an underground stone bothy)

So, after many days of clambering about in thick gooey mud, with chilly water running down my neck, was it all worth it? Well, yes it was. Nigel, Carol Ann, Rachel, Stuart, David, Natalie, Freda, Max, Peter and all the other bat group members I've surveyed with are great company and there's a real feeling of doing something valuable for conservation, even if it's only to strike a site off the list.

Those sites in which we didn't find any bats often produced other compensations. Amongst other things, I've seen four different Barn Owl (Tyto alba) roosts, more Roe Deer (Capreolus capreolus) than you can shake a stick at and some rather attractive grey slugs with a cream stripe (species, anyone?). Plus, loads of fascinating human history: from 3,000 year-old soutterains, through 600 year old castles to World War II bunkers and pill-boxes.

Oh, and I've got through enough Persil to sink a ship....

(Nigel, looking intrepid in a copper mine)

Please remember that hibernating bats are extremely vulnerable to disturbance. Carrying out hibernaculum surveys requires a roost visitor's licence with a specific endorsement. Entering a hibernaculum and disturbing hibernating bats is a criminal offence. Many hibernation sites are also extremely dangerous. If you are interested in doing this type of survey work contact your local bat group, who can help you to get involved legally and without risk of harming the bats or you.

Find your local bat group: http://www.bats.org.uk/batgroups/batgroups_list.asp

More information on the NBMP: http://www.bats.org.uk/nbmp/index.asp

Lothians Bat Group: http://plecotus.co.uk/page_1204624452640.html

My Website: plecotus.co.uk

Hibernating Pipistrelles

Today I spent a very pleasant couple of hours wandering through a semi-ruined castle with members of Lothians Bat group. We were there to look for hibernating bats, which occupy crevices and cracks in the decaying stonework. The most popular spot is in the deep, barrel-vaulted ceilings, which in other old buildings are often used for summer or autumn roosting.


To understand why they are so popular with bats, look at the schematic below. In a typical medieval building, arches and ceilings are built from stone blocks arranged into a curve, so that each is supported by the one outside of it. Above this, the infill is usually made of rubble. Over the years the mortar tends to fall out of the gaps between the stone blocks. As long misguided perfectionists don't repoint the stonework, this creates crevices, some of which may extend into spaces within the rubble fill, creating sometimes quite large bat havens. The downside for us is that surveying these buildings quickly causes a sore neck, from peering upwards, pointing a light into the crevices!


What is particularly interesting about the site we visited today is that, not only is it used by hibernating Brown Long-eared Bats (Plecotus auritus), two of which we saw, it is also used by Pipistrelles (Pipistrellus sp.). Remarkably little is known about the hibernating behaviour of Pipistrelle bats: they are rarely found in the mines and caves where larger British bat species are found hibernating. It is generally assumed that they hibernate individually in small crevices in trees or buildings and are probably more tolerant of fluctutations in temperature and humidity. So it was nice to find at least twelve of them here.

Unfortunately, it isn't possible to say whether they were Soprano Pipistrelles (Pipistrellus pygmaeus) or Common Pipistrelles (Pipistrellus pipistrellus): the physical distinctions are difficult enough with a bat in the hand! However, a braver bat-worker than I might note the dark muzzles and wonder if they might be commons.

Click on the picture below to see a larger version of it and you'll see the brown splodge in the centre resolve into a Pipistrelle's face.

The following two pictures show two groups of bats, sharing crevices. I have no idea how many are hiding behind the mortar in the first picture, but the crevice in the second contained seven bats.

My website: plecotus.co.uk