There is a fundamental problem here in that as soon as a hibernating hedgehog is picked up it will start to arouse. Assuming that you are not going to pick it up how do you plan to measure energy consumption? As always the welfare of the hedgehog is the major concern. I am assuming that you are considering non-invasive methods?

No, I do not want to wake up or transfer the hedgehogs. Maybe one can build a box that is accepted by the hedgehog as a winter nest and that can be made airtight by closings and can be connected to a calorimeter by tubes? Or maybe there are experiences with activity logger and weight measurements? Of course, I want to work non-invasively in any case, therefore heart rate records or other physiologic measurements are probably not possible ...

If an artificial nest box is an option, then this is relatively straight forward for indirect calorimetry. If using a pull mode configuration (i.e. measuring excurrent flow rate) the box does not even have to be perfectly sealed. If providing nesting material, make sure it is not rotting, a "compost heap" can have a quite high metabolic rate on its own. Especially, when comparing it to a hibernating animal.

That is great to hear that you will be working non-invasively with the hedgehogs Anne. As Thomas says, if you can use an artificial nest box this should work well. I have been running York (UK) Hedgehog Rescue Centre for the past 25 years and have often had hedgehogs hibernating, both in the garden and in hutches, while they were being monitored prior to release back to the wild. One thing you could do, to monitor the times when the hedgehog emerges from hibernation, which I am sure you know that they do intermittently - this being known as periodic arousal - is to set up a camera to record these times. You mention recording weight changes. I think this is a good idea. If you are able to have a system set up whereby any weight changes are automatically monitored that would be the best approach. Regarding making the nest box airtight, this is not a good idea as the hedgehog needs a ventilated nest. I'm sure that if you can monitor weight changes this should help a great deal. I have been looking at weight changes both prior to, during, and following hibernation and looking at the triggers involved. It would be interesting to see what results emerge from your study. I wish you the best of luck with it.

@Toni, with a continuous weight measurement that samples at a high enough sample rate, arousals will be easy to detect from the weight record (=> no stable weight as the animal moves). Metabolic rate increases should also help to time periodic arousal. A camera is likely optional.

With an open flow (flow through) system, ventilation will be provided by the gas analysis system. The nest is probably better ventilated than under natural conditions anyway.

@Anne, if you want some local respirometry help, Stefan Hetz at HU (Animal Physiology) may be a great resource (incl. workshop for the boxes) too.

Thank you Toni and Thomas for your really helpful information!