Tuesday, 27 January 2009

Winter Bat Activity

We tend to think of winter as a time when bats hibernate and won't be seen again until spring. In fact hibernation is not as simple as that: bats do awaken at times and move around. Indeed, they are sometimes seen flying in the midst of winter.

This afternoon whilst walking the dogs I spotted a Pipistrelle foraging over the River Esk. It was flying round in circles in the clockwork flight pattern typical of the genus and occasionally dropping down to catch an insect. A feature of winter bat activity is that it happens in daytime, as the higher ambient temperature means there is a greater likelihood of catching enough insect prey to offset the energy costs involved in coming out of hibernation.

I tried unsuccessfully to interest the dogs in the bat, as I have an idea it could be rather useful to have a dog trained to listen for bat calls and alert me when there's a bat nearby. Unfortunately, my pair of canine delinquents find the command "sit" quite challenging, so they aren't likely to succeed in training as bat-dogs.

When I passed by later on at dusk the bat was still hard at work hunting and seemed to be having some success, despite the ambient temperature being only 3 or 4 degrees. I have heard several suggestions as to why bats occasionally feed during the winter. It may be that individuals have been forced out of hibernation because they have failed to build sufficient fat reserves to see them through the winter, but it seems more likely that fluctuations in temperature may cause individuals to take advantage of the opportunity to forage on insects which have become active.

Different bat species have differing requirements for hibernation. Here in Scotland Myotis species, such as Daubenton's (Myotis daubentonii) or Natterer's Bats (M. nattereri) seem to be particularly exacting, hibernating below ground in caves and mines which feature a steady, low temperature, low airflow and high humidity. They usually hibernate in crevices or ledges where the microclimate may be particularly stable.

Brown Long-eared Bats (Plecotus auritus) are less exacting. When found underground they tend to hibernate on walls or hanging from the roof and are often closer to mine entrances than the Myotids.

The least exacting bats are the Pipistrelles, which are rarely found underground, instead selecting relatively exposed holes and crevices, which are more likely to be influenced by changes in the weather. Whether there are differences between the two Pipistrelles is difficult to judge. As they are impossible to differentiate without handling, they tend to be lumped together in hibernation surveys.

Last winter I wrote about a castle where a group of Pipistrelles and a Brown Long-eared were hibernating in crevices within a cellar (See "Hibernating Pipistrelles", February 2008). The castle sits atop a hill and there is a constant breeze blowing through the cellar. Unsurprisingly, no Myotids were found hibernating there.

A hibernating Pipistrelle

Carol and Nigel Terry, our local bat carers noted that a casualty Pipistrelle kept through the winter in a cold room tended to wake up and feed every 10-14 days. It may be that Pipistrelle autecology makes use of winter foraging opportunities and that they choose hibernation sites which better allow them to respond to these opportunities.

My website: David Dodds Ecology

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Sunday, 25 January 2009

Bat-workers & golf carts: be very afraid!

At this time of year there seems little for a bat-worker to do. Hibernaculum surveys are strictly limited, to avoid the risk of disturbance and there are only so many site visits one can do before running out of enthusiasm for assessing bat potential! These are the days when the mind wanders back to highlights of "real" bat work, before the onset of winter.

One such highlight last year was an autumn visit to a well-known golf and country club in the Borders to check and clean the bat boxes. A large group of bat-workers from Lothians and Borders Bat Groups assembled to go round the boxes, checking them for bats and recording the amount of droppings (an indication of how well each box has been used during the year).

I'm not entirely sure whether it shows trust or naivete, but we were allowed the use of a small fleet of golf carts in order to get round the course with our ladders. If you have never seen a conga line of golf carts, full of bat workers and equipment snaking across the landscape you have never known fear!

Fortunately we were accompanied by the course green keeper and one of his team, which probably helped curb the temptation to descend to the level of "Wacky Races". More importantly, it allowed them to see for themselves the great work they have done, making and erecting bat boxes around the course.

Annual bat box checks have several practical purposes. Firstly, the boxes can be cleaned out in readiness for the next year and any damage identified for fixing. Secondly, we have the opportunity to assess the extent to which each box has been used, providing data which shows the progress of the individual bat box scheme and, when combined with other schemes, a rough measure of how bat populations are doing locally. Thirdly and perhaps most importantly, less experienced bat group members get an opportunity to get close to live bats. Many very active bat workers (including me) started off with bats, with the thrill of seeing a Pipistrelle in a bat box.

In South East Scotland it is extremely rare to find anything other than Pipistrelles in bat boxes (with some intriguing exceptions in recent months) and this site was true to that experience. In autumn boxes tend to be used by male Pipistrelles as the base for a mating territory and it is usual to find boxes occupied by either an individual male or by a male and a harem of females. Where boxes are grouped together it is unusual to find more than one occupied, as they would lie within the same territory. The droppings however, often reveal that other boxes have been used, either earlier in the year or in differing conditions, with bats moving between boxes to find optimum temperate conditions.

The course is home to some remarkable buildings and is known to be home to roosts of Brown long-eared Bats (Plecotus auritus), Common Pipistrelles (Pipistrellus pipistrellus) and Soprano Pipistrelles (Pipistrellus pygmaeus). Best of all is a large maternity colony of Daubenton's Bats Myotis daubentonii). Although the roost was breaking up at the time of our visit, we were still able to glimpse a group of around 20 bats clustered together. I took the photograph below earlier in the year, when there were over 50 bats present, with a cluster of Nycteribia kolenatii bat-fly pupae clustered around (you can see them better in the lower picture).

It was a very successful day in terms of finding bats, recording useful data and giving people the chance to get close to bats. Best of all it was that very rare thing: a chance for bat-workers to get together in daylight!

Please note: handling or disturbing bats is a criminal offence without an appropriate licence issued by a statutory nature conservation organisation (Scottish Natural Heritage, Natural England, Countryside Council for Wales, Northern Ireland Environment Agency).

Most bat groups welcome new members and give them the opportunity to take part in events like this. To find your local bat group contact the Bat Conservation Trust

My website: David Dodds Ecology

Thursday, 8 January 2009

An 1892 Bat-worker

As an ecologist whose first degree was in history, I have always had an interest in the development of natural history. I would love to have been one of those wealthy edwardian or victorian country parsons whose lives were devoted to natural history (whilst presumably paying a curate to take care of the religious stuff!)

Last year I heard a talk about the use the Botanical Society of the British Isles makes of historical records in order to understand changes in the distribution of vascular plants. Some of their impressive database comes from the notebooks of victorian botanists and the voucher specimens they made, which are often still to be seen in herbaria. Other records are found by trawling old natural history books and drawing out biological records from descriptions of species and their distribution. Inspired by this I resolved to seek out any such data I could regarding bats in my part of Scotland.

It took a while to find a suitable source of data: bats were not recorded anything like as much as vascular plants were, botany being a "suitable" occupation for those few victorians and edwardians who had time to spare. However, I recently came across a copy of "The Mammalian Fauna of the Edinburgh District", written by William Evans in 1892. In it, Evans set out to record the distribution of mammals in Eastern Scotland between the Tay and the Tweed (a rather broad definition of "Edinburgh distict" by today's standards). He particularly wanted to record the distribution of bats and small mammals, as these were felt to be under-recorded at the time. Arguably then, Mr Evans was one of the first ever bat-workers in Scotland.

There are some fascinating distinctions between the work of this dedicated natural historian and modern bat-work, but some remarkable parallels too.

Not surprisingly, the methods used are utterly different and at times seem a little barbaric to a modern reader. In a day when bat detectors were still 6 or 7 decades away, the art of finding bats was focussed on roosts and upon seeing and catching bats in flight. Whereas today we consider it appropriate to make biological records based on seeing (or hearing) a bat and recording the salient characteristics, in an age when conservation was unheard of and probably unnecessary, the true scientist's voucher specimen was a dead animal. Evans described removing bats from roosts, catching them in flight using butterfly and fishing nets, plus some less savoury approaches. The Daubenton's Bat (then Vespertilio daubentoni, now Myotis daubentonii) seems to have come in for more of it's fair share of hasrh treatment: "During the summer of 1869 I observed a number of bats flitting above a still reach of the Esk above Penicuik, and one which I succeeded in striking down with a walking stick proved to be of this species."

Three other specimens of this species were sent to him from the Dunbar area by a contact who, rather than battering them to death with a walking stick, chose the gentlemanly approach....and shot them!

In another section Evans describes how impressed he was with the nimble flight of a Pipistrelle he watched, though his methods of evaluating this were a little rough by today's standards: "In June last I watched one for fully a quarter of an hour flying in the bright sunshine at Broomhall, near Dunfermline and was much struck with its activity and the facility with which it evaded stones and other missiles thrown at it."

Lest you think too poorly of Evans, he also described caring for live bats (probably captures, rather than the sick and injured bats the modern bat-worker might deal with), in particular a Brown Long-eared Bat given to him by the gamekeeper at Dalkeith Country Park (where there is still a Brown Long-eared roost): "It delights in scrambling about the pictures, the window-blinds and even the chairs; and often settles on the floor, where it moves with considerable rapidity (indeed, it may almost be said to run), keeping the body practically clear of the ground. A more knowing little creature I have seldom seen; and, having discovered that there is sufficient space below the room-door for it to creep through, it's endeavours to overcome obstacles placed in the way of it's escape are most persistent and amusing."

Aside from the very limited equipment Evans had available by modern standards, the victorian understanding of bat taxonomy was rather different. He describes there being 12 species of bat nationwide, whereas today we accept there are 16 or 17 (depending on your views about the Greater Mouse-eared bat's status in the British Isles). The most obvious difference is the Pipistrelle. We now know that there are three Pipistrelle species in the UK, whereas in Evan's day only one was known, the splitting of Common and Soprano Pipistrelles being still a century away.

The most surprising thing about Evan's work and the thing for which he deserves to be remembered is the fact that, despite limited taxonomic understanding and huge limitations in method and equipment, compared with today, his description of the bat fauna of the area is remarkably in tune with what we know today. He described Brown Long-eareds as "by no means rare", Daubenton's Bats as "...locally at least, not uncommon" and Pipistrelles as "undoubtedly by far the most abundant and generally distributed." Ignoring the split of the Pipistrelle species, these three are the most abundant bat species in the region today.

More impressive still is that he was remarkably accurate about the rarer species too. He described a record of Natterer's Bats from near Dalkeith (the two known roosts of that species in the Lothians today are in the Dalkeith area) and goes on to hypothesise that Whiskered Bats are likely to be present in the region too. They are, but there are only three modern records of them in the Lothians. In fact, his only shortfall was his failure to mention the Noctule, which we now know to be present in the Lothians. Whether they were present 117 years ago is a moot point, but it's only in the past decade that they have been identified in south east Scotland. Were they here in Evan's time? We'll never know.

If you're interested in helping to put historical biological records to work, try visiting http://herbariaunited.org/atHome/ This project uses on-line volunteers to transfer information from thousands of old herbarium sheets onto a modern database. It's easy to do and rather addictive!

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