For the past few weeks I have been lucky enough to re-visit the University of Brighton where I undertook my undergraduate degree, to assist with a project on the European hedgehog (Erinaceus europaeus). A current student of Ecology and Biogeography and ex-classmate of mine, Christina Kimbrough is undertaking her dissertation on the survival of hedgehogs post-rehabilitation. The Royal Society for the Prevention of Cruelty to Animals (RSPCA) initiated the study in response to the numbers of hedgehogs bought in for rehabilitation. Although you may think most hedgehogs bought into the RSPCA may be the injured soldiers back from battle with England’s roads, actually a lot of hedgehogs are bought in because they aren’t gaining enough weight for hibernation. They are so common in fact, the RSPCA have gone to the lengths of abbreviating a term for them, ‘TSTH’ meaning ‘Too Small To Hibernate’. Usually TSTH’s are taken in over winter and rehabilitated for release in spring, however there are more hedgehogs than pens to keep them in and money to feed them with. To help reduce such costs, there have been attempts to hibernate hedgehogs in captivity as well as releasing them into the wild once in hibernation. However the former still costs way too much and the latter is currently being looked into at the University of Reading (see http://www.rspca.org.uk/ImageLocator/LocateAsset?asset=document&assetId=1232728996691&mode=prd). Although the final outcome of the study is yet to be defined, its intention is to look into speeding up the process of rehabilitation and releasing hedgehogs in late autumn to see if they are able to adjust and enter hibernation in the wild.
So based on current research what are their chances of survival? Well several studies have actually shown that hedgehogs do very well after rehabilitation and even orphaned hedgehogs that have been in captivity for a long time can quickly adapt to life in the wild. However this is based on studies where hedgehogs were released in spring, not in autumn when they are about to enter hibernation. At this time, hedgehogs should have a good chance of survival if they manage to adjust to their surroundings quickly and find a place to hibernate before loosing too much weight. But this part is crucial. The loss of weight threatens them the most as many studies show that on release, hedgehogs loose weight initially but regain it once they have adjusted to their new environment. Releasing them at this time of the year means that there will be fewer foods available and so the hedgehogs will need to find a safe place to hibernate quickly before their reserves decline. I didn’t have the knowledge to ask this when I was working with Christina, however I expect that a key feature of this study will be to release hedgehogs above the minimum weight (450g) so that they are compensated if weight loss should occur. For more information on this see ‘The new hedgehog book’ by Pat Morris (ISBN: 9781873580714).
I must admit I was a little jealous of Christina when I found out about her project, as not only did she get to handle the species she was studying (my dissertation was spent on my hands and knees searching for hazelnuts gnawed by dormice without the slightest chance of even seeing one), but she got to play around with some awesome radio tracking equipment courtesy of the RSPCA! The equipment used to track the hedgehogs included a radio transmitter, receiver and aerial. The transmitter is the piece you attach to the hedgehog; the receiver is the tool used to tune into frequencies and listen to them and the aerial is used to catch the signal. Christina was kind enough to invite me along to see the transmitter being fitted to the hedgehog, which I will now make an attempt to recall. Firstly, the hedgehog was secured into a position by holding it firmly in one place, then a small patch of its spines were trimmed along the vertebral line on its dorsal side (see pictures below). You have to be careful that the hedgehog doesn’t erect its spines at this point so that the patch isn’t lost! Meanwhile the glue to attach the transmitter was being prepared which was some sort of dental acrylic that I quickly caught whiff of, a very potent smell and Christina quite rightly pointed out its similarity to the smell of a nail salon. The glue was then smoothed onto the bottom of the transmitter, which was then placed onto the freshly trimmed patch of spines and held firmly for a few minutes whilst it dried. The hedgehog was then ready for release, which was undertaken at a site not too far from the University in open grassland with woodland adjacent to it-perfect for hedgehogs.
When it came to tracking the hedgehogs, a tracking team would head out to the release site with the receiver and aerial and tune into a particular transmitter (each transmitter had its own frequency so you can track more than one hedgehog). The aerial is then attached to the receiver and held up horizontally to catch the signal. It is a good idea to start of with a 360-degree turn to begin with and listen out for the beeps, which tell you where the signal is. Once a signal is located you can ‘home’ in on it by steadily moving the aerial until you get the strongest signal, or the loudest beeps. This is then repeated so you have a signal from several different directions to enable triangulation, and Christina recommends 3 for this. Although triangulation is prone to error it is often the only method you can use in scrubby terrain, especially when hedgehogs are burrowed under trees finding places to hibernate. It is always a good idea to brush up on your tracking skills before going out as there are many things to consider when using the equipment. I would discuss them here but I’ve realized that this article is getting rather long, but you can find a good guide on the Biotrack website (http://www.biotrack.co.uk/), as well as information on some of the equipment. Biotrack also mention that you can download a programme called Ranges8 to analyse tracking data with, and after a quick browse of the site I found out there is a demo version free of charge which is perfect for mucking around with if you’re interested (http://www.anatrack.com/home.php)!
Swiftly moving on before I delve to deeply into the subject, the main idea of the project is that the radio tracking equipment can be used to track the movements of the hedgehogs so that Christina is able to keep track of how they are doing through the winter and see how many survive until spring. With any hope, the hedgehogs will do well, although we would be naïve to expect them all to survive! Unfortunately Christina was unable to capture any wild hedgehogs to use in comparison but the study will at least be a starting point and Christina is even thinking about using it as a pilot study in preparation for an MRes or PhD, which could be interesting. I also plan to carry on helping out with the study so I promise to write another article on it if the data reveals any surprises.