Four years of listening to Sark's nights

On the night of 30 July 2022, a bat detector on Sark logged 3,755 echolocation recordings of Common Pipistrelle. That is one species, on one night, on one small island. It was the busiest night for the species in four years of listening, and Common Pipistrelle finished those four years as Sark’s most recorded bat by far.

How the survey worked

The listening was the Bailiwick Bat Survey, run by the British Trust for Ornithology and funded by the States of Guernsey, across four seasons from 2021 to 2024. More than 200 volunteers across the Bailiwick borrowed static acoustic detectors from hosting centres and left each one out for at least four consecutive nights in its own square of 500 by 500 metres. On Sark, the detectors were hosted by La Société Sercquaise. The Bailiwick-wide effort came to 2,364 locations, 9,426 detector nights and 16,192,045 triggered recordings, 4,019,529 of them identified as bats.

Eight species of bat

Sark’s own list from those seasons holds eight named species: Common Pipistrelle, Kuhl’s Pipistrelle, Nathusius’ Pipistrelle, Soprano Pipistrelle, Grey Long-eared Bat, Brown Long-eared Bat, Natterer’s Bat and Leisler’s Bat. The report judges Soprano Pipistrelle and Brown Long-eared Bat probably not resident here. The scale held to the end: in the 2024 season, Common Pipistrelle logged 24,415 call sequences on Sark across two detector nights.

The long-eared bats of La Seigneurie gardens

Grey Long-eared Bat, the third most recorded bat in the Bailiwick, appeared on Sark in every season, peaking at 93 recordings in one night on 3 October 2021 in La Seigneurie gardens. The more suggestive detail sits in its social calls. The species’ D-type calls, the kind often associated with proximity to a roost, were heard from only two islands in the whole Bailiwick, Guernsey and Sark.

A first for Sark at Derrible Head

On 11 October 2023, a detector near Derrible Head caught a Leisler’s Bat, the first ever noted on Sark. The species was new for the whole Bailiwick during the survey, with no earlier records anywhere in the islands, and Sark’s detectors found it again on 28 July and 19 October 2024. The report reads it as a rare but regular migrant to the islands, arriving mainly in autumn.

The bat with no agreed name

One identification stayed open. A large bat was recorded 11 times at a single Sark location over the nights of 7 to 9 September 2023. Two experts judged those calls probably a Parti-coloured Bat, a vagrant to the Channel Islands. A third thought them more likely a Serotine together with a Leisler’s Bat. The identification stands in the record as undetermined: something large crossed one spot on Sark across three September nights, and it has still not been named.

Two records no other island has

The detectors identify other sound producing animals besides bats, and two of those animals were logged only on Sark of all the islands surveyed, in all four seasons: the Black Rat and the Lesser White-toothed Shrew. Brown Rat never appeared in Sark’s data at all. In the 2024 season the Black Rat, Sark’s only rat and one of the rarest mammals in the British Isles, was picked up 29 times, all on Sark and none on Jersey, Guernsey or Alderney. The survey’s first season report also made the first attempt anywhere to describe how the Lesser White-toothed Shrew can be identified by sound.

Why it matters when you visit

There is no street lighting anywhere on Sark, and in January 2011 the island became the world’s first Dark Sky Island, designated by the International Dark-Sky Association. Both facts are about the sky. The four years of recordings fill in what moves beneath it. Walk out after dark here and the stars take your attention first, but the survey says the night around you is busy: pipistrelles logged thousands of times in a single night, long-eared bats in La Seigneurie gardens, a rat and a shrew found on no other island surveyed, and possibly one large bat with no agreed identity. Sark’s dark, quiet nights belong to these animals too, and for four years somebody kept count. The species tables and Sark’s numbers in full are on our bats page, and the Getting to Sark guide covers the journey to the island.