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Monitoring rare and elusive species is critical in guiding appropriate conservation management measures. Mammalian carnivores are challenging to monitor directly, due to their generally nocturnal and solitary lifestyle, and relatively large home ranges. The European mink Mustela lutreola is a critically endangered, small, semi-aquatic carnivore and is one of the most threatened mammal species in Europe. In northern Spain, the European mink population is monitored regionally using different methods and approaches, making assessment of national population status difficult. There is an urgent need to 1) assess the efficacy of survey methods and 2) identify a standard monitoring methodology that can be deployed rapidly and inexpensively over large areas of the mink’s range. We deployed four methods—camera trapping, hair tubes, live trapping, and environmental DNA (eDNA) from water samples—to compare the probability of detecting European mink when present at 25 sampling sites within five 10 × 10 km2, and the economic cost and time required for each method. All four methods successfully detected European mink but the probability of detection varied by method. Camera trapping and hair tubes had the highest probability of detection; however, eDNA and live trapping detected mink in one 10 × 10 km2 where the latter two methods did not. For future European mink monitoring programs, we recommend a combination of at least two methods and suggest that camera traps or hair tubes are combined with live trapping or eDNA (depending on the scale and aims of the study), to gather critical information on distribution, occupancy and conservation status.

After a significant population decline during the 20th century, populations of both greater and lesser horseshoe bats have increased over recent decades in Britain and populations of lesser horseshoe bats have increased in Ireland. Vincent Wildlife Trust (VWT) acquired 37 bat reserves since the 1980s with the aim to safeguard the sites and enhance the roosting and hibernation conditions in buildings that were often derelict and sub-optimal for bats. These measures have resulted in a strong population size increase of all colonies. However, populations have also been increasing throughout Britain and Ireland as a consequence of legal protection and milder winters resulting in higher survival rates. Therefore, it is not clear whether the measures that have taken place in VWT reserves have led to a greater increase than roosts that have not benefited from the same type of management. We aimed to compare population trends of horseshoe bat roosts under VWT management and non-VWT management from 1999 to 2020 in order to assess its effectiveness. For this, we analysed population trends at sites under different management types (VWT and non-VWT) for lesser horseshoe bats in Britain and Ireland and greater horseshoe bats in Britain. Our results indicated that populations in Britain under VWT management have increased by 366% (CI 225% - 580%) for greater horseshoe bats and 188% (CI 125% - 283%) for lesser horseshoe bats. Roosts that did not benefit from the same levels of management increased respectively by 164% (CI 132% - 199%) and 51% (CI 40% - 60%). In Ireland, populations of lesser horseshoe bats in VWT managed roosts increased by 217% (CI 118% - 364%) while non-VWT managed roosts remained stable (-0.44%; CI -23% - 29%). We conclude that management actions carried out by VWT of greater and lesser horseshoe bat roosts have helped populations recover at a faster rate by securing the integrity of buildings, improving access points and by providing optimal microclimatic conditions within the buildings.

Monitoring rare and elusive species is critical in guiding appropriate conservation management measures. Mammalian carnivores are challenging to monitor directly, due to their generally nocturnal and solitary lifestyle, and relatively large home ranges. The European mink Mustela lutreola is a Critically Endangered, small, semi-aquatic carnivore and is one of the most threatened mammal species in Europe. In northern Spain, the European mink population is monitored regionally using different methods and approaches, making assessment of national population status difficult. There is an urgent need to 1) assess the efficacy of survey methods, and 2) identify a standard monitoring methodology that can be deployed rapidly and inexpensively over large areas of the mink’s range. We deployed four methods – camera trapping, hair tubes, live trapping, and environmental DNA (eDNA) from water samples – to compare the probability of detecting European mink when present at 25 sampling sites within five 10×10km squares, and the economic cost and time required for each method. All four methods successfully detected European mink but the probability of detection varied by method. Camera trapping and hair tubes had the highest probability of detection; however, eDNA and live trapping detected mink in one 10×10km square where the latter two methods did not. For future European mink monitoring programmes, we recommend a combination of at least two methods, and suggest that camera traps or hair tubes are combined with live trapping or eDNA (depending on the scale and aims of the study), to gather critical information on distribution, occupancy and conservation status.