We're making this appeal to highlight the slim margins of fat reserves mammals rely on compared to people's average Christmas intake. It's estimated the average person's calorie consumption on Christmas Day alone is enough to sustain 166 bats, 39 dormice or six hedgehogs through hibernation.
It takes wildlife all summer to fatten up for winter – gaining just 4g in some species of bat – on their usual diet of insects. Lowering their body temperature and heartbeat during hibernation, mammals use very little energy throughout the winter months, with 80-90% of their fat reserves used to wake up when the temperature is warm enough. If disturbed, most won't have enough energy stored to re-enter hibernation and make it through to spring.