Jim Foster, ARC’s Conservation Director, investigates our milder winters and what they mean for the UK's frogs, toads, newts, snakes and lizards.

The recent cold snap affecting much of Britain has taken some by surprise, yet these chilly conditions were the norm, historically speaking. As I write this, there are snow showers in many parts of Britain and overnight temperatures will often hit minus 5C. We have become used to milder weather over the winter months in recent years, as climate change takes hold, and so these icy spells feel unusual. Indeed, the forecast predicts much milder, wetter conditions as we move into the third week of January, with minimum night temperatures climbing to 10C in some areas.

What do these changing weather patterns mean for amphibians and reptiles? These animals generally take a long rest over winter, often finding places underground to hibernate, tucked up well away from freezing conditions. As the climate warms, however, we are noticing changes in behaviour. Milder weather can tempt amphibians and reptiles out of their winter quarters, and most years ARC receives reports of newts in ponds in January, apparently in full breeding condition – something unthinkable when I was first studying amphibians. Snakes and lizards, too, sometimes make an appearance when the winter sun is strong enough, much earlier than the spring emergence discussed in standard text books. There is now good evidence that emergence from hibernation and breeding are shifting to earlier in the year, presumably in response to our changing climate.

At ARC, we are investigating the implications of these changes in behaviour. One obvious consequence is that some habitat works taking place over winter now carry a higher risk of harming animals. Previously, it was fairly safe to assume that amphibians and reptiles would be out of harm’s way if you carried out habitat improvements from November to February. Whilst this remains a useful guide, there does seem to be an increasing chance that animals will be active, and therefore at some risk, under certain circumstances. Some amphibian workers have wondered if the traditional survey season should be extended so that searches start earlier, and this is likely to become more pressing as the climate warms.

When animals are active over winter, they use energy to some extent and it has been shown that for some species like the common toad, this may affect their subsequent body condition and survival. There may be a particular problem for amphibians, which would normally feed on invertebrates in spring and summer, as these would be scarce over winter even with a degree of warming. For great crested newts, one study showed that fewer individual newts survived following milder, wetter winters, although the precise reasons are not fully understood.

Interestingly, it is often sudden shifts in weather that trigger activity. With the abrupt shift to milder evenings next week, it’s likely that amphibians in parts of southern England will emerge from hibernation and start spawning. Reacting to weather changes like this makes biological sense, though a more extreme climate can pose risks. Spawn laid early in the season can freeze if there is a subsequent cold snap, or may fall victim to fungal infection. Recent research by ARC Trustee Rebecca Turner showed that adders in Cornwall emerge from hibernation earlier as a result of milder winters but then face an increased risk of encountering ground frosts. Researchers use the term “climate trap” for these unfortunate circumstances.

There are many other implications of evolving winter conditions. We have identified, for example, that the longer “growing season” for plants means that habitats now require more management intensity, and that some invasive non-native species and diseases may get a toe-hold whereas in the past they’d have been excluded by extreme cold. ARC will be reporting on these issues and more later this year, as we think that climate change has wide-ranging consequences not just for how the animals behave, but also how conservation should operate.

If you’re lucky enough to have amphibians in your garden pond, I hope the above doesn’t cause too much alarm. As a society, we certainly need to take more action on climate change, but warming does not mean that your frogs, toads and newts are about to disappear entirely. You can help by providing them with good quality habitat, and by submitting records of the animals to our monitoring programmes. The latter, in particular, will help us keep track of changes in their behaviour, which in turn helps with planning conservation action.

  

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Selected scientific references

Beebee, T. J. C. (2018). Climate change and British wildlife (Vol. 6). Bloomsbury Publishing.

Griffiths, R. A., Sewell, D., & McCrea, R. S. (2010). Dynamics of a declining amphibian metapopulation: survival, dispersal and the impact of climate. Biological Conservation, 143(2), 485-491.

Reading, C., & Jofré, G. (2023). The relationship between temperature, growth rate and body condition of Bufo bufo toadlets prior to their first hibernation. Amphibia-Reptilia, 1(aop), 1-12.

Reading, C. J., & Clarke, R. T. (1995). The effects of density, rainfall and environmental temperature on body condition and fecundity in the common toad, Bufo bufo. Oecologia, 102, 453-459.

Turner, R. K., & Maclean, I. M. (2022). Microclimate‐driven trends in spring‐emergence phenology in a temperate reptile (Vipera berus): Evidence for a potential “climate trap”?. Ecology and Evolution, 12(2), e8623.

Walker, G., Fairclough, B., & Paterson, E. (2019). Winter presence of adult male palmate newts (Lissotriton helveticus) in a pond in Scotland. herpetological Bulletin, 149, 24-27.