Grantham Ecology

There was a report last month of the first greater horseshoe bat recorded in Ireland*. Ireland is missing a number of species which are common on the mainland; most famously snakes but also woodpeckers and the noctule bat amongst others. Perhaps, like woodpeckers which are increasingly recorded, the greater horseshoe might be about to establish itself but it seems more likely to be an individual who is lost, blown over from the mainland perhaps. This is one of the rarest species of bat in the UK and its range is restricted to the south-west of England and the south of Wales. The reason for this range is largely climatic, partly related to landscape features and perhaps also linked to the availability of suitable roosting sites, particuarly for hibernation*.

This species, surprisingly, turns up in the biological data records around Grantham – the National Biodiversity Network (NBN) has a recording of this bat just beside Melton Mowbray, some 10 miles to the west of Grantham and a good 100 miles from the tip of its normal range. The site of the record was once a mine, now home to bats – principally myotis species such as Natterer’s bats – which gather in mating roosts in the autumn and then hibernate through the winter. The members of the Leicestershire and Rutland Bat Group, who monitor the site, got quite a surprise when they found that, alongside the usual small, crevice roosting myotis bats was a large, free hanging greater horseshoe who had settled beside them for the winter. Most of our UK bat species, contrary to popular depiction, actually roost sideways, face up or face down in holes, cracks or crevices. The only two species who you will always find in the  classic upside-down bat-hang pose are the two members of the Rhinalophus genus, the greater and the lesser horseshoe. The greater horseshoe in this mine therefore stuck out like a sore thumb, hanging by its weak back legs, wings wrapped tight like a cape around a bat the size of a small pear. Where this species spent the remainder of the year is unknown, but for several years it returned to this winter roosting site although it has now been absent for some 20 years.

It could be that this individual was part of a colony within the species’ normal range and made an exceptional commute to cooler winter climes, or even is a member of a hitherto unknown northern colony but it is much more likely that he became lost or separated from his usual range, perhaps due to bad weather or the destruction of a roost, and was simply making the best of his new situation and continuing to lead a horseshoe lifestyle as best he could, admittedly without the company of his kin. Herein lies the long-term problem, without a mate he was never going to establish a new population. This is the difference between the range of a species and the tolerance of individuals; it may well be quite possible for a bat to exist outside of their normal range for a period of time but it is a different matter to expect a population to survive and thrive. Horseshoe bats are relatively long lived for such small mammals; they are known to reach 30 years*. The disappearance of this individual after only a few may be due to old age or migration to a more suitable habitat. But it could be that the winters were a little too cold, the landscape was a little too fragmented, the range of suitable roosting sites was too lacking to suit the year-round changes in conditions.

This is why we must conserve species where thrive, rather than assume they will be fine whilst numbers are still good and concentrate conservation around the edges. Greater horseshoe bats used to be much more abundant within their range in the UK as little as a century ago – a Victorian naturalist suggested they be counted in their roosts by the square yard as the individuals were too numerous and densely packed to count each. I wonder if they would believe tgat now a roost of 20 bats could be considered large. The parallels can be drawn with other species which are common but declining; starlings still seem to be everywhere but there are only 20% the number there were 32 years ago* and a continued decline of this magnitude could soon see them relegated to a rarity alongside the horseshoe bat. Many species of butterfly, including the meadow brown, have undergone similar population drops in recent years.

The great crested newt often receives a bad press for holding up development and the economics-uber-alles mantra of the current government has led them to conclude that we should opt out of the European level protection afforded such species. It is true that, compared to species such as the horseshoe bats, stone curlews, pine martins and the large blue butterfly, the great crested newt is not exceptionally rare in this country. But on an European level, it is, and that is why it is so important to take care of it here, where it is in its range and where it can flourish if care is taken to safeguard its habitat.

We often can not see the big picture if we simply look out of the window and extrapolate to the rest of the county, or country, or continent. You would never expect to see a greater horseshoe bat foraging through woodland on the edges of Grantham. Similarly, you would never expect to see the day when starlings, brown hares or meadow browns were extinct in the UK but the recent State of Nature report indicates startling declines in the populations of a wide range of native UK species. Never say never.