Life after Light – Bats along Grantham Canal

It’s very nearly Halloween – what better time to introduce you to the bats which haunt Grantham Canal when darkness falls…

IMG_4159I spent several nights this September cycling along Grantham Canal with an EM3 bat detector connected to a GPS unit, recording the bats in flight between the A1 to the east and Hickling Basin to the west. Bats use echolocation to navigate and hunt and the bat detector converts this ultrasonic sound into something we can hear. The sound emitted by the detector tells you when a bat is there, often which species it is and sometimes even what it is doing.

You might imagine that this is quite a sinister place to be, surrounded by bats on a moonlit night, but there really is nothing to be afraid of! As the detector tapped and pattered away to announce their, I could see bats flying before me in the darkness. But even though I was cycling towards them, they elegantly avoided me every time, never making contact and certainly never tangling in my hair. This is one of the most enduring myths about bats but their fantastic echolocation abilities mean that they can ‘see’ and avoid obstacles on even the darkest of nights.

I recorded at least five species in September, some calls with ‘buzzes’ indicating foraging and some with ‘song flight’ where male soprano pipistrelles emit lower frequency social calls to attract mates. These are just on the edge of human hearing and can be heard without a detector – you may have heard the very high frequency chirrups if you walk outside at dusk in the autumn.

Common Pipistrelle

The Common Pipistrelle is one of the smallest but certainly the commonest bat species in the UK
The Common Pipistrelle is the smallest and the commonest UK species

The common pipistrelle is our most abundant species in the UK, and was encountered throughout the route of the canal, particularly where there are more trees as this species specialises in hunting along ‘edge’ habitat which is typically along hedges, tree lines and other landscape features.

The orange bat symbols in this map indicate the locations where common pipistrelle bats were identified. The A1 which dissects the canal is at the far eastern end with Hickling Basin marking the western extent
The orange bat symbols in this map indicate the locations where common pipistrelle bats were identified. The A1 which dissects the canal is at the far eastern end with Hickling Basin marking the western extent

Soprano Pipistrelle

The soprano pipistrelle is physically similar to the common pipistrelle but a has differences in morphology such as wing veination and face colouring with the much darker face of the common pipistrelle earning it's other name of bandit pipistrelle
The soprano pipistrelle is physically similar to the common pipistrelle but has differences in morphology such as wing veination and face colouring with the much darker face of the common pipistrelle earning it’s other name of bandit pipistrelle

The soprano pipistrelle is very similar morphologically and was not even identified as a separate species until 1992. Now they can be told apart confidently in their hand, and with fair reliability acoustically as the soprano pipistrelle calls at 55 kHz compared with the common pipipstrelle at 45 kHz. In England, the soprano pipistrelle is often found associated with water and so it was no surprise to find them along the canal. An interesting observation however is that there appears to be much more activity to the east, near to larger water bodies. Denton Reservoir lies just beside the canal towards the eastern end and is likely to be an important foraging resource for this species.

aaaa
The blue bat symbols in this map indicate the locations where soprano pipistrelle bats were identified. The A1 which dissects the canal is at the far eastern end with Hickling Basin marking the western extent

The vast majority of the recordings related to these two pipistrelle species – the other  bat species were found at much lower frequencies.

The yellow bat symbols in this map indicate the locations where Natterer's bats were identified; black represents whiskered/Brandts; purple represents brown long-eared; and green represents noctule. The A1 which dissects the canal is at the far eastern end with Hickling Basin marking the western extent
The yellow bat symbols in this map indicate the locations where Natterer’s bats were identified; black represents whiskered/Brandts; purple represents brown long-eared; and green represents noctule. The A1 which dissects the canal is at the far eastern end with Hickling Basin marking the western extent

Noctule

The noctule bat is our largest species and tends to fly high and early, often the first bat to appear around sunset and can be seen in the skies as the swifts are still on the wing. Only one noctule was heard during the transects, between Denton and Woolesthorpe and picked up again near Muston. This bat is large and the sky was light meaning I could watch it  flying my way, foraging as it flew to the west. This is a widespread species which favours roosting in trees, but numbers are generally lower than the pipistrelles.

Noctule bat - the largest UK species
Noctule bat – the largest UK species

Brown long-eared bat

Brown long-eared bat is one of our quietest but most charismatic bats. Their large ears make them quite charming to behold, and they are frequently found roosting in barns and other buildings. I only picked up a single instance of this bat, but their very quiet echolocation means they are generally under-recorded.

The brown long-eared bat is named for quite obvious reasons!
The brown long-eared bat is named for quite obvious reasons!

Myotis bats

The myotis bats are considered to be some of the most difficult to identify from sound alone. Daubenton’s bats are the myotis species most frequently associated with water as they specialise in flying low over still waters and taking insects on the wing or from the water’s surface. Natterer’s bat is another myotis species and some of the calls recorded along the canal in September are characteristic of this species. Whiskered and Brandt’s bats are the other two myotis species which are likely to be present in this part of the country. These two bats are very similar to one another and are difficult to separate even in the hand. Some of the calls have the characteristics of one (or both) of these two species. Whilst these species are not commonly associated with aquatic habitats, the canal also boasts hedgerows, copses and grass bank margins which provide great terrestrial habitat as well.

A Daubenton's bat - the myotis species most frequently associated with water. The myotis bats are larger than the pipistrelles but not as big as the noctule.
A Daubenton’s bat – the myotis species most frequently associated with water. The myotis bats are larger than the pipistrelles but not as big as the noctule.

I encountered a whole host of other species whilst cycling along in the afterglow of sunset including barn owls, tawny owls, hares fleeing down the towpath and badgers snuffling in the hedgerows. The canal is stunning in the daytime but at night it comes alive with a whole host of new species – a walk around sunset might reveal creatures which you would not normally be privileged enough  to watch.

Sunset along Grantham Canal

If you are looking to commission bat surveys in the Midlands area, check out Landscape Science Consultancy’s website here!

Advertisements

Robin’s pincushion

Have you spotted the tufts of green and red fibrous tendrils sprouting from dogrose? These are known correctly as a Bedeguar Gall but are known to many by the colloquial name Robin’s Pincushion.

Bedeguar Gall or Robin's Pincushion
Bedeguar Gall or Robin’s Pincushion

They are a type of gall – this is commonly defined as an abnormal plant growth caused by some foreign agent (such as a fungus, a mite or a wasp) which provides both food and shelter for the organism. In this case, the mechanism is a chemically induced distortion of unopened axillary or terminal leaf buds by a tiny wasp which has the latin name Dipoloepis rosae. The species name – the second of the two latin names – is rosae which refers to the intimate relationship between the wasp and the rose.

The female wasp lays her eggs on the rose and, a week later, the larvae hatch and induce the formation of the gall. The gall provides food for up to 60 larvae as they grow throughout the summer, passing through various ‘instar’ forms or life stages. Inside the centre of the gall is a woody core with chambers where the larvae spend the winter in pupal form and then begin emerging as adults in May, continuing through to August. The wasps are tiny – only 3-4mm across – and most are female.

Bedeguar Gall or Robin's PincushionThe galls are more common on plants under ‘stressed’ conditions such as those growing in waterlogged soil or with poor nutrients, however the presence of the galls does not appear to have a significant impact on the plants.

These photographs were taken on Beacon Hill behind Grantham where many of the rose plants have been visited by the wasp, but they can be seen in hedgerows and scrub patches throughout the country.

 

Hibernating drone flies

It’s autumn and those creatures which hibernate through the winter are beginning to make their preparations. The squirrels are out burying nuts to tide them through, the bats are fattening up on insects to see them through torpor and those invertebrates which sleep the winter away are looking for safe places to stay.

A likely indicator of a hibernating insect is an early appearance in the spring. This is true of the brimstone butterflies which, for many, heralds the start of spring, and also the rather ungainly named drone fly. This is actually a hoverfly – Eristalis tenax – which is named not for the sound it makes in flight but for its similarity to a honey worker bee, a drone. These flies can often be seen early in the springtime, taking advantage of the first available nectar sources such as the lesser celandine pictured below.

Drone fly - Eristalis tenax - on a lesser celendine
Drone fly – Eristalis tenax – on a lesser celendine

We visited Tattershall Castle last weekend – a National Trust property out near Lincoln – and spotted several of these drone flies investigating crevices and cavities in the roof of the kitchen at the ground floor of the castle. You descend here down a small flight of steps and this movement below the ground will appeal to the hoverflies – conditions tend to be more stable and remain above freezing when you are beneath the ground level. Stability of conditions is often as important as suitable temperatures – a stable environment means less false signals that spring is here and emerging from hibernation too soon is never a good idea!

Drone fly investigating a hibernation site at Tattershall Castle
Drone fly investigating a hibernation site at Tattershall Castle

The hoverflies were not alone – tattered small tortoiseshells and red admiral butterflies were also checking up and down the walls for a safe place to roost for the winter whilst herald moths were already settled and looking set to sleep until spring.