I recently completed three days of small mammal (mammals under 50g) surveying in collaboration with BTCV and Bury Council in order to gain some firsthand experience in the processes involved in ecological surveys.
The three days were composed of multiple activities including; cleaning, preparing and placing traps, collecting and recording specimen details, and completing a one day course in small mammal ID and ecology.
My first experience in this activity was in baiting and placing the traps. For this particular survey, 25 Longworth traps were used. This number is considered the minimum sample size required to collect representative data. Moreover Longworth traps are considered the most reliable tool for sampling small mammals. To prepare the traps a large fistful of straw is packed into the holding area of the trap before adding some form of food for potential captives. Whilst dried fruit and seed is a suitable source for the omnivorous mice and voles, casters (fly pupae) are required to nourish shrews due to them being obligate insectivores.
Prepared traps were placed across 4 sections of Phillips park at a ratio of 2:1:1:1. Within each area the traps were placed an even distance apart, and always along linear landmarks such as hedges and logs, preferred routes and refuges for small mammals.
The traps were set the evening before the first day of the survey and were subsequently checked each morning, early afternoon and evening over which the survey spanned. It was vital that we checked the traps regularly as small mammals have a very high metabolism. Shrews for example may need to eat their own body weight in food every 24 hours. Unchecked traps, especially in cold conditions, could quickly result in specimen death.
After inspection, traps that had not been triggered were simply placed back in their previous location. In the cases of successful traps, the animals inside were removed for analysis, and the traps themselves were re-set with new bait and bedding. With small mammals being nocturnal, the majority of successful trappings were recorded in morning surveys.
Caught specimens had their species, sex, weight and location recorded before release at their capture site. To obtain this data it was necessary to handle the animals, and we were taught a pretty successful approach for doing this. Triggered traps were emptied into a see-through plastic bag and nest material was removed to leave the mammals alone. From this stage, the animal was guided into one corner of the bag and grabbed firmly with one hand, to prevent it struggling. Using our other hand, we were taught to reach into the bag and gently lift the animal by pinching the loose skin on the back of its neck. This technique, if done correctly causes the animal to become rigid, making it easy to identify its sex and species. Animals were weighed within their plastic bag using hanging scales with the weight of the bag being subsequently deducted. Throughout the survey, surgical gloves were worn for hygiene purposes and also to offer some protection from potential bites.
During the survey both shrews and mice were caught, however unfortunately no voles. During the days in which I helped out only wood mice were caught which was a bit disappointing. Nevertheless there were plenty of the critters, giving me ample practice at handling and sexing the animals.
This particular species (woodmouse), one of the 10 small mammals native to Britain, has a number of characteristics through which it can be identified.
As with all mice, this species is characterised by a relatively long (equal or more than body length) thin, tail. Characteristics of the wood-mouse include a predominantly brown fur coat with a white underbody. On close inspection a small, coloured throat patch is also evident (see photo above). This yellowy throat patch should not be mistaken for the more extensive yellow throats of the similar yellow-necked mouse.
Overall, I feel I learned a lot from this course, my first real experience of animal surveying. Having the opportunity to learn more about the native species in Britain, not something my degree particularly focused on, as well as getting hands on experience with animal handling and identification, I believe, has been invaluable. I look forward to completing similar courses soon, and hope also to complete other animal surveys with local groups.