Welcome to the summer newsletter which covers news about the survey and the highlights from the months of June, July and August.   

The main headlines for the summer months were (i) a new species for the Guernsey - Serotine and (ii) an explosion of bush crickets!

As in the previous two months, Common Pipistrelles continue to dominate and make up approximately 95% of the calls identified as coming from a species of bat. They are widespread across the island and are not discouraged by artificial light, unlike species like Grey Long-eared Bats. It is noticeable that there are more squares where long-eared bats are absent in areas like Town, the harbour, St Sampson and around the Airport, where artificial lighting is present. We have not done any formal analysis yet but will be looking at bat activity and light once we have cleaned up the data set which now numbers 405,000 bat recordings!

The Serotine records mirror what happened in Alderney. Between 1 and 14 July there were 14 square nights on which this species was recorded. In Guernsey it was first recorded on 18-31 July and we had 13 square nights on which it was recorded, plus an extra record on 17 August. It is tempting to think that the bat flew round Alderney for a couple of weeks and then flew to Guernsey, but that is probably fanciful thinking and their actual status is a bit more complicated than that!

Serotines are relatively easy to identify from their sounds. Being a ‘big’ bat (or at least much larger than a Pipistrelle!) their calls are at a much lower frequency – around 30 kHz. Like the Alderney records, there did not seem to be any particular pattern in where they occurred in Guernsey but there was possibly a concentration around the Talbots and Fauxquets Valleys. One of the first to be recorded was in an urban St Peter Port garden and since then there have been records from the north and south of the island. We have not yet had a chance to check every single record, but every record we have checked is genuine.

The classifier also identified over 100 instances of other bat species including Lesser Horseshoe bat, Greater Horseshoe bat, Soprano Pipistrelle, Brown Long-eared bat, Nathusius' pipistrelle, Brandt’s bat and Daubenton's bat. Smaller numbers of Barbastelle, Noctule, Leisler’s bat and Whiskered bat were identified by the classifier (80 records in total).  We have checked a few of these but they were odd calls of other species. We have now identified the source of many of the horseshoe bats as being a faulty detector which was putting out electrical noise that was incredibly similar frequency to the horseshoe bat! This detector has been returned to the manufacturer for replacement. It was still recording bats but was intermittently putting out this noise.

For the rarer species, we will have to wait until October when we download the remainder of the recordings from the cloud. Once your recordings have been uploaded and identified, they are put into ‘deep glacial storage’ which means that although the storage costs are much cheaper, but this comes as a cost as we have to plan further ahead as to when we can download them. We have currently pulled back 3.5 terrabytes of data from Amazon Glacier storage which takes us up to the beginning of September. It has taken over a week of solidly downloading to get this far! We will re-run all the recordings through the latest classifier and will be looking at the data over the next few weeks.

The Serotine is one of the largest bat species in Britain and measures 6-8cm in length and weighs between 15-35g. They are usually one of the first to appear in the evening, often when it is still fairly light. They can often be heard squeaking loudly just before they emerge at dusk. They have broad wings and a distinctive flight pattern with highly manoeuvrable flight in a slow flapping motion, often making short glides or steep descents.

Serotines have long, dark brown fur and a pale yellowish-brown underneath. Their wings, face and ears are dark brown or black. Juveniles have darker fur than adults.

Most of its food is caught within 2km of the roost which consists mainly of flies, moths and beetles, particularly chafers and dung beetles. They pluck insects from the ground or from vegetation and also catch prey in flight. Serotines can also eat large insects while in flight, manipulating the insect in their jaws and chewing off the hard wing-cases which are dropped to the ground. They fly at about tree-top height and are often known to feed near streetlights where moths have been attracted to the light.

Serotines make extensive use of buildings and are thought to roost in them almost all year round and therefore are hardly ever found in trees. They roost mainly in older buildings with high gables and cavity walls. As they are so building-orientated, one of their greatest threats is that they are very vulnerable to disturbance during building work and the use of toxic chemicals in remedial timber treatment.

Artificial light does not only can impact bat numbers as a recent paper has shown (click here to access it), street lighting, especially environmentally friendly LED lighting, has an enormous impact on the number of moths in the area. The abundance of moth caterpillars in hedgerows by rural roads in England was 52% lower under LED lights and 41% lower under sodium lights when compared with nearby unlit areas. We have traditionally thought of the often catastrophic global insect declines as being due to three major factors - land use change, pesticide use and climate change - but light pollution clearly plays its part. The image below from https://www.lightpollutionmap.info clearly shows the major sources of lighting on the island around St Sampson, St Peter Port and the Airport. Bat friendly street lighting is possible – in The Netherlands, using red street lighting has been shown to have less impact on bat usage and this has been trialled in the UK. Look at how dark Sark is, fully justifying its Dark Skies status.

Late summer is, to be honest, a bit of a trial for bat workers using passive recording devices to record bats. Bush crickets produce sounds in the ultrasound range and so trigger bat recorders. Some species may stridulate only during the day and part of the night, but many will also make noise throughout the whole of the night. They can be incessant so if a cricket is next to a recorder and making noises throughout the night, the SD memory card can fill up with huge amounts of bush-cricket noises!
 

We like to think of this as an advantage as we can add another group to our list of species we can monitor. On the flip side, the size of the uploads can be massive and, in Guernsey, it is fair to say that our system has struggled with some uploads. We have not seen this elsewhere and so have looked at the code we use to make it more efficient. We have identified some areas where we can make efficiency savings in the programming and expect uploads to process in about a quarter of the time. If your upload fails and returns “No Ids”, don’t worry, your recordings are safe and we will reprocess them once we download everything.

We realise we have work to do in classifying bush cricket calls. There are a lot of Dark Bush Crickets being recorded and this is a species which has not been recorded in Guernsey before. The problem seems to be that there are so many Great Green Bush-crickets being recorded that when they call over each other, they look similar to Dark Bush Cricket. We will be looking in more detail at this over the autumn and winter. Dark Bush Crickets do occur in Jersey, so we will be looking carefully at the recordings to see if we can identify genuine records. Roesel's bush-cricket and Short-winged bush-cricket tend to call mostly during the day so we would not necessarily expect to see large numbers in the data but it will be interesting to see where they are recorded from. In Guernsey there is a coastal bias in the Roesel’s distribution as might be expected as most species rich, low intensity grassland is in coastal areas. However, it is encouraging to see this species in a few areas inland as well.

We only ‘turned on’ the bush cricket classifier on 1 July which is around when they start to stridulate, hence we do not show figures for June.

The number of uploads for August is lower than for June and July and we expect more records to come in as some people have left memory cards for us to upload. We will update the figures at the end of the season.

If you haven’t already done so, please book your detector slot for the second survey of your selected square for this season as soon as possible. We still have lots of availability in October at all of our Bat Centres.

Our survey period is only running until the end of October so don't miss out! 
 

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