An increase in changing weather patterns is negatively affecting hazel dormouse populations that are already struggling, according to new research led by a Manchester team.
Scientists concluded that fluctuating winter temperatures – as opposed to constant cold temperatures – an increase in rainfall and denser populations of dormice are all having an impact on the survival of the species.
The study, published in Animal Conservation, which was led by Manchester Metropolitan University and supported by wildlife charity People’s Trust for Endangered Species, warns that without mitigating these factors, dormice could disappear from our woodlands altogether.
By studying long-term data gathered on 4,000 animals from four UK and one in Europe, researchers were able to investigate exactly what impact changing local weather patterns has on population growth rates, and how these interact with other factors contributing to the species’ decline.
Dr Fraser Combe, former PhD student at Manchester Metropolitan University, and lead author of the study, said: “Our results showed that increased rainfall, fluctuating winter temperatures and density dependence are all contributing to the species’ decline.
“As population density increases, a population can reach carrying capacity, resulting in more individuals competing for food and nesting sites.
“In areas where food and shelter are plentiful this is less of an issue, but lack of sympathetic woodland and hedgerow management leads to less diverse habitat.
“This, combined with increased fragmentation of habitat patches, means that the number of dormice those areas can support is lower. The plights of these populations is exacerbated by a changing climate.
“When a population is at capacity, a bad winter or a year of fluctuating and unusual weather has a stronger and more negative effect on dormouse populations than during a stable winter.
“We also found that although warmer and wetter weather impacts dormice of all ages, there were subtle differences between adults and juveniles.”
The research showed that in adult dormice, both winter survival and fecundity – which is the ability to breed successfully – were negatively impacted by increased average temperatures and higher rainfall, especially when these patterns of warm, wet weather were interspersed with cold periods.
It’s not uncommon for hibernators to wake up intermittently, but frequent waking depletes the adults’ energy reserves by the time they wake in spring, thereby hampering their breeding capacity.
A bad winter or a year of fluctuating and unusual weather has a stronger and more negative effect on dormouse populations than during a stable winter.
Juveniles were impacted both before hibernation and over winter. If juvenile dormice don’t build up enough fat reserves before winter, their chance of surviving hibernation is slim. That, combined with waking up early or more frequently and being forced to be active when they should be asleep and when there’s less food around, has serious consequences too.
But the study did offer some cause for optimism. Conservationists can help mitigate against these negative effects, giving dormice a fighting chance.
Measures such as coppicing, improving hedgerow quality and connectivity between suitable habitats, planting diverse tree species that fruit and flower in varying seasons, and host an abundance of invertebrate species, and creating plenty of scrubby edge habitat can provide more nesting sites and ensure year-round food availability.
This will help improve resilience through periods of unpredictable weather pattens, and hopefully enable dormice to better survive winter and successfully breed come spring and summer.
Nida Al-Fulaij, Conservation Research Manager, People’s Trust for Endangered Species, said: “Hazel dormouse populations have fallen by a staggering 51% since 2000, and they’re listed as vulnerable to extinction on the Red List for Britain’s Mammals 2020.
“Understanding what is driving this decline is critical, so that we can put measures in place to prevent further decline, restore populations to stable levels and ultimately stop dormice from disappearing from our woodlands and hedgerows.”
