This Autumn we launched our campaign to keep wild hedgehogs out in the wild for as long as possible. Here are some of the relevant links to research.
Climate change is affecting weather patterns and temperatures. Here in the UK, the weather is warmer now, with the UK average temperature for September 2021 at 14.7 C - this is over 2 degrees warmer than the average between 1981 and 2010 and October 2020 had minimum temperatures 0.5 degrees warmer than average. Climate summaries - Met Office.
Hedgehogs hibernate when temperatures are consistently below 5 degrees C (Reeve,1994) - that's more than 1 night of frosty windows. Until then, they are active, and eating up as much as possible.Even in hibernation, they awake every 7-11 days.
Hedgehohgs can hibernate successfully from as little as 450g (Morris, 1984), although minimum survival weights can vary by country (Jenson, 2004) . Hoglets can double their birthweight in a week and can be 6 times their birth weight by 3 weeks (Reeve, 1994). All hoglets can reach hibernation weight by 3 months old (Reeve, 1994). So smaller hoglets in September and October can be up to weight by the time the colder weather arrives.
Research shows that hedgehogs that were released from rescues in the winter at 600g had the same changes of survival as their wild counterparts (Yarnell et at, 2019). Hedgehogs were released throughout the winter, whenever temperatures were above freezing (0 deg C) for 5 nights after release and were then monitored by researchers. The findings mean rescues can safely release throughout the winter months whenever it is above these temperatures and the hedgehogs are over 600g. There is no need to rescue hedgehogs that are at this weight.
So why are we so keen to keep hedgehogs in the wild? Hedgehogs kept in captivity for long periods, can lose their survival skills (Miller, 2000) and they can experience stress in captivity (Rasmussen, 2021) - in short, it doesn't do them any good and we may be doing more harm rescuing them if they don't need it.
That doesn't mean we don't think there are times when hedgehogs need rescuing.
Any hedgehog out in the day at this time of year is likely to need to be taken to a rescue. Equally, when temperatures start to drop, smaller hedgehogs may then need extra help.
Please check local temperatures and contact your local rescue if you are concerned about a small hedgehog.
1. Reeve, N. (1994) Hedgehogs, T & A D Poyser, Ltd, London. ISBN 0-05661-081-X
2. Morris P (1984) An estimate of the minimum body weight necessary for hedgehogs (Erinaceus europaeus) to survive hibernation. J Zool Lond 203:291–294
3. Jensen AB (2004) Overwintering of European hedgehogs Erinaceus europaeus in a Danish rural area. Acta Theriol 49:145–155
4. Yarnell, R.W., Surgey, J., Grogan, A. et al. Should rehabilitated hedgehogs be released in winter? A comparison of survival, nest use and weight change in wild and rescued animals. Eur J Wildl Res 65, 6 (2019). https://doi.org/10.1007/s10344-018-1244-4
5. Rasmussen, S.L., Kalliokoski, O., Dabelsteen, T. et al. An exploratory investigation of glucocorticoids, personality and survival rates in wild and rehabilitated hedgehogs (Erinaceus europaeus) in Denmark. BMC Ecol Evo 21, 96 (2021). https://doi.org/10.1186/s12862-021-01816-7