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/