Hazel dormouse numbers show a small recent rise after long decline

What you need to know

• The recent improvement is modest beside the long-term loss. LBC reports an almost 10% increase from 2020 to 2025, but says the monitored population remains 59.4% below its 2000 level. 2
• The figures should be read as a trend in monitored sites, not an estimate of every dormouse in Britain. PTES’s 2023 report describes its index as relative abundance at those sites. 3
• PTES monitoring commentary records estimated overwinter mortality of 31% in 2024/25, which it describes as unusually low, alongside high spring litter numbers. These observations may help explain the recent signal, but do not establish its cause. 1
• Warmer, drier spring and summer conditions could have improved food availability and breeding opportunities, according to LBC’s reporting. The same coverage notes that prolonged drought and variable winters could also have adverse effects. 2
• Habitat availability and management remain important pressures in the UK government’s assessment. Sources also identify habitat management and connectivity as important, so a short-term rise does not remove the need to address those pressures. 412

Why this matters

The change offers a reason to examine whether conditions for dormice are improving, without mistaking a recent uptick for recovery. Clear interpretation matters because the long-term trend remains sharply negative and the role of weather is unsettled. 234

What happens next

PTES says more data are needed to assess any link between weather and dormouse survival. The reporting also leaves open how the recent increase was calculated and how it relates to an earlier estimate of a 70% decline from 2000 to 2022. 123

What we know

• LBC reports an almost 10% rise in the monitored population between 2020 and 2025. 2
• The 2023 PTES report recorded a 70% decline in its monitored index from 2000 to 2022. 3
• The government assessment describes the hazel dormouse population as continuing to decline overall, with habitat among the pressures. 4

What we don't know

• The reporting does not explain how the 59.4% long-term decline figure relates methodologically to the earlier 70% estimate. 23
• The sources do not establish whether warmer, drier seasons caused the recent increase or distinguish their effects from habitat, food supply, breeding and winter survival. 12
• The available reporting does not specify the methods, confidence intervals or site coverage behind the 2020–2025 increase, or how well established woodland monitoring represents other habitats. 23

Read the reporting

This WildNews briefing synthesises and summarises reporting from the sources below. WildNews did not produce the original reporting. Learn more about how we use AI