Water Voles Disappear from Long Mead
On the 2nd of May four areas of watercourse at Long Mead Wildlife Site were surveyed for signs of water vole (Arvicola amphibius). In previous years there was abundant evidence of water vole presence on these watercourses, but unfortunately this year no evidence was found. The habitat is still considered to be highly suitable for water voles, suggesting that predation is the primary reason they are no longer present.
Water vole populations have seen sharp decline across Britain in recent years due to two main factors: habitat loss and predation by the invasive American mink (Neovison vison). In 2024 evidence of American mink was found at Long Mead during water vole surveys. Water voles are highly vulnerable to predation by mink, therefore it is likely that presence of mink is the primary reason that no evidence of water voles was found in 2026.
In the natural water vole population cycle, around 70% of the population do not survive the winter. During breeding season, beginning around April, water voles become fiercely territorial and spread out away from core winter territories to avoid competition. The population then rapidly expands during the breeding season and spreads out further to colonise new areas of habitat. As the surveys at Long Mead were undertaken at the beginning of the breeding season, it is possible that any remnant populations of water voles on un-surveyed watercourses may recolonise the surveyed ditches by the end of the breeding season.
Furthermore, it is suspected that water voles retreat from Long Mead to higher ground overwinter to avoid flooding. If the population has been significantly reduced by mink predation there may not yet have been need for individuals to return to establish breeding territories. Therefore, it would be beneficial to conduct further surveys at the site in September to see if a water vole population has re-established.
This could be supplemented with raft monitoring which may help to detect water vole presence at a low density. The water vole mitigation handbook provides the following advice on using rafts: “In some cases artificial latrine sites can be used to aid the survey, formed from pieces of ‘Cellotex’ or other equivalent cavity wall insulation material which is buoyant, but which unlike polystyrene, does not break up into small balls. The rafts should be approximately 60cm x 30cm, positioned within vegetation at the toe of the bank at a density of one per 10m and tethered in place.”. Placing camera traps observing rafts and ‘baiting’ rafts with food attractive to water voles such as apple can also be an effective way to detect water vole presence.
Finally, in order to protect water vole populations and allow them to permanently reestablish, it will be important to ensure that Long Mead is mink-free. The BBOWT Water Vole Recovery Project have been undertaking mink trapping in Oxfordshire, which could be an option to explore at Long Mead too.