Threat to rare Barbastelle bat population at Lark Rise Farm

The proposed East West Rail line poses a severe threat to one of the UK's rarest mammal species - the Barbastelle bat (Barbastella barbastellus) – that has been identified as present in the Westfield area of Lark Rise Farm, where a proposed railway line will cut directly across nature-friendly farmland.  

Recent acoustic monitoring has revealed critical bat activity patterns that demonstrate the railway will intersect a key foraging corridor between the Special Area of Conservation at Eversden and Wimpole Woods and active hunting grounds at Westfield. This represents a potentially catastrophic impact on a species with very few known maternity colonies in the UK. 

The Barbastelle bat (below) is classified as one of the UK's rarest mammals by the Joint Nature Conservation Committee (JNCC). The species has an extremely limited distribution, with few known maternity roost sites across the entire country. This makes every active colony of exceptional conservation value and legally protected under both UK and European legislation. 

 The JNCC acknowledges that "Barbastelle ecology is relatively poorly known," making the protection of known active areas even more critical. The species is "likely to have been significantly under-recorded within its range," suggesting that documented populations may represent only a fraction of actual numbers, emphasising the importance of protecting all known sites and surrounding land. 

The recent acoustic monitoring at Westfield by the CRT has revealed exceptional biodiversity. Using the British Trust for Ornithology's (BTO) Acoustic Pipeline software for species identification, up to eight bat species were recorded, demonstrating the site's importance as a multi-species habitat. 

Common Pipistrelles were in abundance, indicating rich insect prey availability and the confirmed Barbastelle presence was recorded to the east of the proposed railway alignment, bringing the species into a direct collision course with an active railway line.  

The Bourn Brook, a tributary of the River Cam, provides a natural navigation and foraging corridor connecting these areas. Other bat species recorded were Brown long-eared, Daubenton’s, Leisler’s, Noctule, Serotine, and Soprano Pipistrelle.  

Eversden and Wimpole Woods is designated as a Special Area of Conservation (SAC) specifically for its Barbastelle bat colony. The JNCC site description confirms it is a 'summer maternity roost where female bats gather to give birth and rear young'.  

Detection equipment was used in November 2024 and May and August 2025, with Barbastelles visiting the site on each occasion. This suggests that Westfield functions as part of an essential ecological feeding corridor throughout their active months, including seasons when it will be dark during busy times on the railway.

Barbastelle maternity roost sites are located 4km  west of the proposed railway at Eversden and Wimpole Woods, and active foraging areas with recorded Barbastelle presence are located east of the proposed railway at Westfield. Barbastelle bats can forage up to 10 kilometres from their roosting sites. This places Westfield well within the active foraging range of the Eversden and Wimpole Woods SAC, making it integral to the colony's health.  

The proposed East West Rail alignment creates a lethal barrier exactly where it will cause maximum impact with the maternity roosts located to the west of the railway. Regular movement between these areas is necessary for colony survival, but if the East-West Rail route is constructed, it will create a high risk of train collision. 

Given the rarity of Barbastelle maternity colonies in the UK, even a small number of casualties could have severe population-level consequences such as loss of breeding females to collision and disruption of foraging patterns. Habitat fragmentation could isolate the colony from essential resources. 

The connection between Westfield and the Eversden and Wimpole Woods SAC means that impacts at Westfield could constitute damage to a European-designated protected site. This triggers the highest level of environmental protection under UK and international law. Barbastelle bats are protected under the Wildlife and Countryside Act 1981. Any project that could harm this species requires comprehensive assessment and mitigation that may not be technically feasible given the collision risk scenario. 

Regulatory authorities have a legal duty to ensure that infrastructure projects do not threaten the survival of rare species populations. The evidence from Westfield suggests this duty cannot be fulfilled with the current railway alignment. 

Standard railway mitigation measures are inadequate for addressing Barbastelle collision risk. Bat bridges or tunnels cannot accommodate 10km foraging ranges and habitat creation elsewhere cannot replace established foraging territories.

The CRT asked East West Rail to see the design of their bat crossing points at a meeting in January, but were told they had not been designed at the time. 

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Published: September 2025