The Society’s passive bat detector has been hard at work almost every night since mid-March. Left outside in members’ gardens or other secure locations it triggers automatically and records bat calls as they fly over. The use of the new Acoustic Pipeline service from the British Trust for Ornithology (BTO) has allowed the recordings to be analysed and verified much more easily. Society members have been very helpful in hosting the detector in their gardens again this year

In August there was huge excitement when our detector recorded the social calls of the extremely rare Kuhl’s pipistrelle, sparking national interest amongst bat enthusiasts and even reported in the Daily Telegraph. Over three nights in August, our bat detector was set up in the garden of a retired ChiNats member in Aldwick. Among the 1,400 records logged were 55 audio recordings that contained the social calls of Kuhl’s pipistrelle. It is likely that these would have been missed if it wasn’t for our use of the BTO’s Acoustic Pipeline. This new system identified these calls automatically as Kuhl’s Pipistrelle, and so flagged that something special had been recorded at this location, prompting an excited email from staff at the BTO.

Normally found around the Mediterranean, Kuhl’s Pipistrelle is believed to be a rare visitor to Britain with only a handful of records to date. Kuhl’s pipistrelle can easily be overlooked because it produces echolocation calls that are very similar to Nathusius’ Pipistrelle, which is commoner in the UK, but its social calls are different and diagnostic. The records have now been verified by Kuhl’s Pipistrelle expert, Neil Middleton, and accepted by the Sussex Bat Recorder, Sally-Anne Hurry.

Dr Stuart Newson, lead scientist on bat monitoring at the BTO, told us, “I am really excited by this finding. It is thought that the range of Kuhl’s pipistrelle is expanding northwards, so it is interesting to speculate whether this represents a vagrant or an establishing population”.

Kuhl’s Pipistrelle was first identified in 1817 by German naturalist Heinrich Kuhl and named after him. It is similar in size to a Common Pipistrelle with a body length 40 – 50mm (about 2 inches), wingspan 210 – 250mm (about 8 ½ – 10 inches) and weight 5g – 10g (about ¼ ounce).

A new tool for analysis and interpretation of the results from ChiNats Bat Recording Project.

The Society has agreed to subscribe to the new ‘Acoustic Pipeline’ system offered by the British Trust for Ornithology (BTO) for analysing and storing our bat recordings. The system provides the infrastructure to allow audio recordings (wav files) of bats and other creatures to be uploaded to a secure server maintained by the BTO, to be processed to find, identify and verify biological sounds, and to return results back to the Society. The cost will be about £100 per year plus a one-off cost of £300 to upload the existing records.

At the start of the ChiNats project we were fortunate to be given free access to software developed by the British Trust for Ornithology (BTO) to analyse the bat calls recorded and identify the bats. However, this is only a semi-automated process. The data from each session must be uploaded onto Ken and Linda Smith’s computer and fed into the BTO classifier programme. Each file recorded is analysed and given a suggested identification with a confidence threshold, this takes a couple of hours of computer time. In a typical night with say 1000 recordings each result must be checked manually against the threshold and accepted or rejected to compile the list of bats present through the night. This takes us another hour or two for each set of recordings.

There is also a significant issue of safe storage of the data. At present we have data for three years totalling 1800 Gigabytes stored on the ChiNats freestanding hard drive and backed up on Ken and Linda’s own free standing hard drive. (2020: 550 Gigabytes of data stored in 430,972 files; 2019: 521 GB in 384,907 files and 2018: 602GB in 540277 files).

The other advantage is that the results are shared with the National Bat Recording Scheme and shared with the Sussex Biological Records Centre. This data sharing was not possible previously.

Ken and Linda have been testing the new Acoustic Pipeline, the recordings from the bat detector can be uploaded directly into the BTO system and the results are returned within a few hours in an easily accessible form.

An update by ChiNats members, Linda and Ken Smith.

We are pleased that, despite everything, we have been able to gather lots more bat results this year.  In March when the weather turned warm enough for bats to be active, the country was in COVID-19 lockdown. So we deployed the automatic detector in our own garden in North Chichester almost every night. This has gathered vast quantities of data which we have not analysed yet (see below).

Once lockdown conditions eased, we loaned out the detector as normal in a COVID secure way. We primed the detector, members collected it and set it up in their own gardens for a few days and then returned it for analysis of the results. We recorded at ten new locations and seven repeat visits.

Three bat roosts were found. Large numbers of Soprano Pipistrelles were detected emerging from the roof of a house in the Summersdale area.  Another large Soprano Pip roost was recorded at a farm building at Appuldram, with thousands of encounters over the three nights. A Common Pip roost was found by us in an old farmhouse at Chilgrove.

Jim Bagley investigated the impact of ‘bat friendly’ red streetlights installed in Hanger Drive, a new development on the old airfield at Tangmere, for four nights between 21-25 August. The analysis confirmed 249 recordings of calls of Common Pipistrelle bats. The chart shows the number of Common Pipistrelle calls through each night. Note, the number of calls does not equate to the number of bats, as an individual bat may fly near the detector many times, but there were clearly good numbers of bats visiting the garden throughout the night of 23/24^th when the weather was warm with no rain. As well as the Common Pips, other less common species visited the garden.

·         The very similar Soprano Pipistrelle visited on two nights. One or more Noctule Bats were recorded each night at around 8:30-9:00 pm.    On 23/24 there were records of a rare Barbastelle at 9:31pm, a Serotine at 11:46 and a Brown Long-eared bat at 11:30 and12:50.

The MacFarlane family used the detector to compare the number of bats in their two Bognor gardens through the night. You can see in the chart below that most of the bats were seen between 9:00-11:00pm but a few were around all night. The numbers were similar, Julia and Bruce (blue bars) had a total of 94 and Heather (orange bars) had 106, mostly Common Pipistrelles (about80%) with a few Soprano Pips and Serotines each night.

The bat detector also records the temperature through the night. This is nicely illustrated in the results from the Hamblin Centre in Bosham (thanks to Kim Fleming for organising). The number of bat encounters in each hour period through the night on left axis (blue bars); temperature, ^oC, on right axis (orange line).

In the autumn, the detector helped with a project for the pupils at Seaford College. They borrowed the detector and placed it at two different locations where they are planning to carry out habitat restoration in the grounds. The students analysed the full ‘raw’ results in a series of spread sheets . There were 7333 recordings logged over the two nights, Noise 1170; Birds 146; Bats 3051 and Crickets 2965.  Our analysis showed they had nine different species of bat at the site. The most numerous were Soprano Pips but also included Barbastelle, Serotine, Nathusius' Pip, Common Pip, Brown Long-eared and possibly Daubenton's, Whiskered, Natterer's bats. The recordings of crickets possibly included six species, calling all night, Speckled bush-cricket and Dark bush-cricket, and small numbers of possible registrations of Long-winged conehead, Grey bush cricket, Roesel’s bush-cricket and Great green bush cricket. There was also one call from a Wood Mouse.  The Seaford college students plan to borrow the detector again, after they have completed the restoration work, to monitor any differences.

2019 Bat recording in and around the Chichester area using an automatic bat detector

The project to record bats flying at night in the Chichester area has been very successful so far and has continued through 2019.

A summary of the results for 2018 is available on the legacy projects page of the ChiNats website.

For 2019, Ken and Linda Smith continued to co-ordinate the arrangements for deploying the detector and downloading and analysing the results of each recording session. As well as giving all members the chance to record bats in their own gardens, we have used the detector on the Medmerry grasshopper survey (not very successfully) and the immediate bat detector at Northwood and Chichester Canal Field Outings.

If you would like to host the detector for a couple of nights in your garden or other suitable location please get in touch with project co-ordinators, Linda and Ken Smith, email kenandlindasmith@gmail.com or see their bat project webpage at www.woodpecker-network.org.uk/index.php/news/38- bat-monitoring-in-chichester-area

Project co-ordinators - Ken and Linda Smith.

2018 Bat Monitoring

The project to record bats flying at night in the Chichester area has been very successful so far and will continue in 2019.
The automatic detector has a microphone sensitive to the range of frequencies of calls made by bats when flying and feeding. The recorder is active all night, every time it is triggered by a bat call it records for 5 seconds. All recordings are stored on a little memory card and we have some clever software to analyse the data and match the calls with the different species of bats. Because the detector is vigilant all night, it gives much more comprehensive results than a hand-held device.
From April to October 2018, the bat detector was placed in 51 different locations in Chichester and the surrounding area (within an approximate eight-mile radius of the city) mostly in ChiNats members’ gardens from Nutbourne to Chilgrove to Slindon to Selsea. It has successfully recorded for a total of 160 nights collecting over 75,000 bat records involving at least 10 different bat species. Records of the less common species will need to be reviewed by a bat expert, but we are confident that bats are found everywhere.
The provisional results so far