Needs Ore Bat Survey 2021

Static bat recorders were set up at various places around the reserve – the Wardens Hut at Needs Ore Point, Black Water Hide, Pullen Hide, the fence line near Mary Monts Bungalow, the Viewing Gate overlooking the Flooded Fields, Shore Hide, Stagg’s Wood and Gravelly Marsh. I also set up a detector at Lepe.

More than 30,000 individual bat calls were detected during the nine month recording period (March to October). Software was used to interrogate the .wav files and initial automatic identifications were suggested by the software.

Where I have given a total of recordings for each species (e.g. Soprano pipistrelle 19,192) this is based on the automatic identifications suggested by the software. The auto ID is not 100% reliable, it’s not feasible to manually check these identifications but these auto ID totals do give a good idea of the abundance of different bat species across the reserve.

For the rarer species these automatic identifications were manually checked and discussed with the County Recorder, Nik Knight.

Eleven species of bat were recorded on the reserve including rarities Greater horseshoe bat, Barbastelle, Nathusius’ pipistrelle, Leisler’s bat and the intriguing possibility that Grey Long-eared bats are also here. Another three myotis species of bat were also recorded but are too difficult to separate on call alone.

Soprano pipistrelle

The two commonest bat species found in the UK are Common and Soprano pipistrelle. Pipistrelles appear fast and jerky in flight as they dodge about pursuing small insects which the bats catch and eat on the wing. A single pipistrelle can consume up to 3,000 insects in one night! They generally emerge from their roost around 20 minutes after sunset and fly 2-10m above ground level searching for their insect prey, which they catch and eat on the wing by ‘aerial hawking’.

Populations of pipistrelles have declined dramatically in the last few decades, partly as a result of modern agricultural practices.

Soprano pipistrelle is the commonest species of bat at Needs Ore with more than twice as many recordings (19,192) as the Common pipistrelle (7,443). This may well be because Soprano pipistrelles prefer wetland habitats including lakes and rivers as well as woodland edges, tree lines and hedgerows.

Soprano pipistrelles were recorded regularly from all of the detectors.

Common and Soprano pipistrelle were only identified as separate species in the 1990s. With a bat detector the peak intensity of the call is around 55kHz for Soprano pipistrelle and 45kHz for Common pipistrelle.

Soprano pipistrelle, frequency line shown at 55kHz

Common pipistrelle

The second most common species of bat at Needs Ore with 7,443 recordings spread across all of the bat detectors.  

Compared to the Soprano pipistrelle they are more generalist feeders found in a wide range of habitats comprising woodland, hedgerows, grassland and farmland.

The peak intensity of the call is around 45kHz.

Common pipistrelle, frequency line shown at 45kHz

Nathusius’ pipistrelle

Nathusius’ pipistrelle is a rare bat in the UK.

It is a migratory species with the first confirmed record of Nathusius’ pipistrelle at Needs Ore flying past the Warden’s Hut on 9th April, six minutes later the same bat was recorded off the car park at Lepe, that’s 28kph for the 3km. They migrate back to their breeding areas in Latvia using this stretch of the coastline.

There were 30 recordings with most during the peak migration period of August to October (bats heading west) and with most recordings from the Warden’s Hut at Needs Ore Point reflecting their migration route along the coastline.

Echolocation calls of Nathusius’ pipistrelle are similar to those of the other pipistrelles, however, the peak intensity of the call is lower than the other two pipistrelle species (see above) at about 38kHz.

Nathusius’ pipistrelle, frequency line shown at 38kHz

Noctule

The Noctule is the largest British species and is usually the first bat to appear in the evening, sometimes even before sunset. They have a characteristic powerful, direct flight on narrow pointed wings. They fly in the open, often well above tree-top level, with repeated steep dives when chasing insects. Noctule bats can fly at 50kph.

The Noctule is still a relatively widespread species in much of England and Wales but has declined owing to modern intensive agricultural practices resulting in the loss of suitable feeding habitat such as permanent pasture and woodland edge/hedgerows.

The recording software suggested 1,606 recordings during the survey period making it the third most common species at Needs Ore. Noctules were regularly recorded from all of the detectors.

They echo locate with a characteristic alternating of two call types with peak frequencies of 24kHz and 19kHz.

Noctule

Serotine

Closely related to the Noctule the Serotine is one of Britain’s largest bat species and usually one of the first to appear in the evening, often emerging in good light. The serotine is far less common than the Noctule. 27 recordings were made mainly from around Black Water Hide and Shore Hide.

The spectrogram below was made near the Viewing Gate and in open situations like this the peak frequency is around 25kHz, unlike the Noctule it does not produce alternating calls of two frequencies.

Serotine, frequency line shown at 25kHz

Leisler’s bat

Very similar to Noctule but slightly smaller. Rare in the UK.

There were 455 Leisler’s bat recordings made during the survey with the bulk of the recordings from around Black Water Hide. This number significantly over estimates the population here as they are very difficult to separate from Noctule and Serotine by call and a good number of the auto identifications are probably incorrect and likely refer to Noctules.

Nevertheless it is possible to confirm Leisler’s bat with a long enough recording to show a clear alternation between two call types peaking at 27kHz and 23kHz, which are above those for Noctule.

Leisler’s bat, frequency lines shown at 27kHz and 23kHz

Myotis species

The myotis genus of bats are very difficult to identify in the field. While it is possible to identify Daubenton’s bats and Natterer’s bats from echo location calls (see the next two species) it is more difficult to identify other myotis bats. There were many recordings which were auto identified as Bechstein’s, Whiskered or Brandt’s bats but these are best recorded as myotis species given how difficult they are to separate.

Daubenton’s bat

Also known as the water bat it has a steady flight, often within a few centimetres of the water surface where they take insects, sometimes directly from the water surface using their large feet as a scoop. Daubenton’s bat is fairly widespread up to northern Scotland.

There were 352 recordings making it the fourth most abundant bat on the reserve although there is the distinct possibility that some of these records may be other myotis bats. A positive identification of Daubenton’s is best confirmed by seeing the bat flying low over the water catching their insect prey. A classic echolocation includes a rapidly descending frequency modulation sweep from 81kHz to 29kHz.

Records were mainly from the water bodies at Black Water and Pullen.

Daubenton’s bat, frequency lines shown at 29kHz and 81kHz

Natterer’s bat

Natterer’s bats have a slow to medium flight, sometimes over water, but it is more often associated with woodland habitats. Much of the prey is taken from foliage and includes many flightless or day-flying insects. Sometimes larger prey is taken to a feeding perch

Natterer’s bat is one of the myotis bats and so identification needs to be made with caution. Natterer’s bats can usually be confirmed by the very low end frequency down to 20kHz and the high start frequency of 100kHz plus.

74 Natterer’s bat recordings were made from all areas of the reserve.

Natterer’s bat, frequency line shown at 20kHz

Barbastelle

The barbastelle is very rare, found in southern and central England and Wales. Very few breeding sites are currently known in the UK. They prefer pastoral landscapes with deciduous woodland, wet meadows and water bodies, such as woodland streams and rivers.

The first record for Needs Ore was an individual recorded from Pullen Hide on 26th June. The same individual (or possibly a small number of other Barbastelles) were subsequently recorded along Warren Lane in the early autumn with the main concentration being around Shore Hide. 

The spectrogram shows the frequency modulation sweep from 44kHz to 29kHz in around 4.5ms. The records have been confirmed by the County Recorder.

Barbastelle, frequency lines shown at 30kHz and 40kHz

Greater horseshoe bat

The highlight of the year was a Greater horseshoe bat recording flying past the Warden’s Hut at 11:30pm on the 19th September. This is a significant record for Hampshire and has been confirmed by the County Recorder.

The Greater horseshoe bat has shown a marked decline and it is rare in Britain confined to the South West and South Wales. It is estimated that the number of Greater horseshoe bats has declined by over 90% in the last 100 years.

The echo location is pretty unmistakable with calls at around 85kHz with a characteristic hoop shape and similar shaped harmonics at half the frequency, 42.5kHz.

Greater horseshoe bat

Brown long-eared bat

Brown long-eared bats are gleaners, often flying slowly amongst foliage, picking insects off leaves and bark. They are known as ‘whispering bats’ because their echolocation sounds are very quiet. The difficulty in picking up these quiet echolocation calls may account for the relatively low number of recordings (49). You typically need to be within 5m of the bat to get anything useable.

Brown long-eared bats were recorded from all areas of the reserve but less so from the more open areas.

Their echolocation calls include two harmonics, the first a sweep from 55kHz to 24kHz and the second a sweep down to around 51kHz.

Brown long-eared bat, frequency line shown at 24kHz and 51kHz

possible Grey long-eared bat

Perhaps the most intriguing record is the possibility that we have Grey long-eared bats at Needs Ore. This species is very rare found only in a few places in southern England.

There were 40 recordings which the auto identification software recorded as Grey long-eared bats. They are very difficult to distinguish from the more common Brown long-eared bat and no doubt most of these recordings will be the commoner species. However, several of my recordings were considered by others to be probable Grey long-eared bats, including the recording below, but given the rarity best recorded as a plecotus species.

Their echolocation calls are slightly lower than Brown long-eared bat (although there is overlap) and also include two harmonics, the first a sweep from 45kHz to 21kHz and the second a sweep down to around 44kHz.

Grey long-eared bat, frequency line shown at 21kHz and 44kHz

The County Recorder has commented that as “Grey long-eared bats are so rare we have to be very cautious. However, we have DNA evidence from droppings recovered from roosts near Lepe so it is possible. Over the years we have had 6 verified records of GLE from the south of the New Forest from Ringwood to Lepe, although two of those were the same ringed bat taken into care on dates 5 years apart!”

If I can build up a substantial database of likely Grey long-eared bat calls then the County Recorder has said that he may commission some trapping to collect DNA, make in the hand measurements or to collect droppings if they can be found.

Chris Button, Natural England Voluntary Warden February 2022

6 thoughts on “Needs Ore Bat Survey 2021

  1. Great to hear of so many varieties of bats at NO! what a great effort and so interesting.

  2. This is brilliant Chris. Just goes to show what’s out there. Hope you can keep going with this and get permission to trap.

    1. thanks Andy, this season I’m concentrating the detectors in areas I suspect Grey long-eared are present and hopefully will get enough good data to get the county recorder involved.

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