Wildwood Trust is a project situated on the edge of the Forest of Blean, in Kent. Wildwood’s aim is to use the facilities in the woodland and animal collection to ‘support practical conservation projects in the wild.’ There are over three hundred animals, many of which are endangered, taking part in conservation projects, and living in semi natural enclosures. The woodland is managed by coppice rotation, a process that takes place every 20 years where trees such as silver birch and sweet chestnut are cut to ground level and then shoots allowed to regrow. This is an essential habitat for the hazel dormouse.
The wood is a centre for captive breeding and reintroduction for native endangered species such as hazel dormice and this example will be used in this report to explain these issues.
The Hazel Dormouse
The Hazel Dormouse is native to the countryside of Britain, predominantly southern England (see figure 2), living in woodland areas and environments rich in coppice. The mice are an arboreal species; spending the majority of their life in trees or bushes and only living on ground level during winter hibernation. The mice are considered a ‘flagship species’ chosen to represent an environmental cause and raise support subsequently benefitting other species contained in the ecosystem.
The populations of dormice were shown to have disappeared from seven counties in England by The UK Mammal Society Dormouse Survey in 1984. The decline has been caused by human destruction of their woodland habitat through development, climate change and pressure from other species. Grey squirrels were introduced into England and ate the nuts that the dormice fed on whilst they hibernated. Climatic change caused warmer winters resulting in the early awakening of the dormice from hibernation, before the ripening of their food, and wetter summers stopped the dormice from foraging.
Dormice are listed on The World Conservation Union (IUCN) Red List of Threatened Species and are protected by law, under Schedule 5 of the Wildlife and Countryside Act, 1981. This act prevents the killing, injuring, disturbing or trapping of the dormouse. It also makes it illegal to possess or control the animal, damage its shelter and sell or buy the dormice without a licence.
Captive breeding is the reproduction of animals in confinement under controlled conditions to be released into the wild. This is important for conservation of threatened species and is an example of ex situ (out of the natural habitat) conservation, but it raises implications. Captive breeding has taken place at Wildwood for dormice as part of the national dormouse captive breeding and reintroduction programme.
The dormice are housed in an enclosure made of a wooden frame and mesh covering. Unlike other rodents theirs is a short breeding season having 1-2 small litters of 4-7 offspring. The young stay with the mother for 6-8 weeks, making it unlikely for more than one litter a year. In each enclosure the nest boxes are kept 1.5m off the ground with protection from water and predators, water and food are hung on the side of the cage and the floor is covered with leaves and soil. After hibernation the enclosure is filled with branches of vegetation to provide 3D space for the animals to use. This provides the ideal conditions for breeding with no stressful food finding. One enclosure can hold up to three individuals either two females and one male or one breeding pair and their offspring, under one year of age, and will be kept in the same groupings over winter. Adult males must be placed separately as they are territorial and will fight.
Where do the breeding mice come from?
In November nest boxes are checked and, if permission is granted from Natural England, wild dormice weighing less than 15g can be taken. As these mice are underweight they have less chance of surviving winter hibernation and can be kept indoors during this period in heated nest boxes. Other dormice are orphaned or given into rescue centres and vets. The Common Dormouse Captive Breeders Group (CDCBG) chooses which individuals breed and how many are bred annually, which also helps to prevent inbreeding.
The Paignton zoo studbook keeper gives each captive born dormouse a stud book number, and their breeder will allocate each mouse a local ID number.
When animals reproduce genes are passed from parents to offspring. Genetic variation is the natural differences of individuals, across a population. A characteristic that will give dormice a disadvantage, for example short teeth, could prevent them from opening nuts, so if food was in short supply these mice would die and longer teethed mice would thrive. This would cause the gene for longer teeth to become more common, which is the basis of natural selection. Natural selection, was a theory of Charles Darwin, in which better adapted animals would have more chance of survival, so becoming more predominant.
Wildwood would like to preserve biodiversity which is the huge variation found within and between species and ecosystems on Earth.
Offspring that are created from the same sets of genes will have similar genes to each other. Inbreeding is the breeding of animals that share more genes than the average population, they are related in some way. If inbreeding takes place the genes of their young will come from a very selective gene pool, making particular genes more predominant within a species. Inbreeding can lead to deformities and mutations as well as problems with immune systems and an increase in genetic diseases. ‘Inbreeding tends to reduce the number of alleles in a population’, from source 1.
A studbook for dormice was created in 2006 to keep track of mice kept by members of the CDCBG. The studbook limits inbreeding and keeps breeding to first generation or wild caught animals. Breeders can use the studbook to selectively breed, mixing mice from different collections and different families. This will stop related mice from dominating the gene pool creating healthier mice and preserving genetic diversity.
Future developments could include implantation of embryos and in vitro fertilisation (IVF) of the dormice. Selective breeding could be improved and gradually undesirable characteristics or weaknesses bred out. Cloning could be developed.
Captive breeding raises many ethical, environmental, social and economic issues.
* There are various ethical issues that need consideration with regard to captive breeding. Animals have to be removed from their natural environment and put into captivity virtually locking them up and many people feel that there should not be any interference with nature in this way even to avoid extinction. It could be the case that genetic diversity has already declined to the point where it is irreversible.
* There could be a case for protection to encourage breeding in the wild, by in situ methods of conservation, within the environment. However, captive breeding is used to retain species and improve numbers and is easier to manage.
* Selective breeding increases genetic variation and produces healthier populations also preventing inbreeding. This reduces deformities and mutations but should humans interfere with natural reproduction? Inbreeding would sometimes naturally occur and if the population was kept large enough this would not often happen.
Visitors pay an entrance fee at Wildwood and this money goes towards the captive breeding scheme. However, they do not see the programme taking place as they would disturb the dormice and interfere with hibernation and reproduction.
It could be that unless the programme continues indefinitely a lot of investment may be lost if the numbers continue to decline.
Using dormice from different collections to breed may spread diseases to other populations of dormice.
Reintroduction is releasing captive born animals into a particular environment to which they were once native and where they will be free from human supervision. Normally these populations experienced decline due to human intervention and will only succeed if the cause of the decline has been overcome. The reintroduction is considered successful if the animal has fully integrated into the local population and survived with no further aid or interaction from humans. Reintroduction projects must follow guidelines set out by the IUCN and Wildwood has released dormice back into their natural habitats. They use a soft release program, gradually using less human intervention.
Seven weeks before release the litters are health screened at the Zoological Society and released if they pass the tests. Reintroduction is limited to once a year as criteria for suitable sites are extensive and complicated. The population densities are less than 10 adults per hectare in their best environments.
What does the health screening test for?
The health screening takes place to check the animals do not have any disease that could be passed onto wild populations.
Scientists test for:
* pathogenic bacteria
* Tapeworms (cestodes)
* Roundworms (strongyles)
The condition of the dormice’s coat, skin, face, genitals, feet and incisor teeth are checked and their weight should be between 18-24g for summer re-introduction. 8mm Pet-ID microchips are fitted in the dormice under anaesthetic for identification in the future.
Where is a dormouse released?
An ideal site for the dormice…
be an old wood with different layers of vegetation,
already have a dormouse community (males may kill new dormice)
have lots of undergrowth,
have less than 100 nest boxes in the woodland.
have deciduous trees,
Place males less than 100m apart, as they are territorial.
have coppicing taking place regularly,
Have related dormice close by to stop inbreeding
have fruiting hazel,
Be at least 20 hectares,
have a site management plan.
Figure 4: Table showing an ideal site for dormouse reintroduction.
How Wildwood release their dormice
1. Natural England is informed.
2. Pre-release cages made of wire are attached to a group of hazel trees.
3. 2-3 nest boxes placed in each cage, with a male and two females so there is more of a chance of the animals staying together.
4.Dormice then live in these whilst they acclimatise to the surroundings.
5. For 2-3 weeks humans supply fresh food everyday, during the day so the dormice are not disturbed. Also leafy branches are placed above pens to provide shade and protection from predators.
6. One week to 10 days into the three week period, a hole, less than 3cm2 is made in the top corner of the cage. The mice can then explore the area and there cage can not be invaded by birds or squirrels.
7. The frequency of feeding is reduced gradually until mid-September, when the animals should have found their own food supplies.
8. The nest boxes are checked until October, where weights and number of offspring are recorded.
9. Dormice are left to hibernate.
10. Monitoring begins in May.
Figure 5: Stages of reintroduction
What is monitored and when does it take place?
A long term monitoring plan should be made before any reintroduction, so that the species will successfully survive in a wild environment. After release nest boxes are checked by trained and licensed volunteers, who record numbers, sex, weight, breeding condition and offspring.
The volunteers monitor the nest once a month from April to October, between the 15th and 25th of each month. Data should be collected before midday so torpid dormice can be seen, and a National Dormouse Monitoring Programme Record From must be completed.
Conditions of release
* Winter cleaning of empty boxes.
* Dormice are released in June to prepare for hibernation.
There is an ethical duty for reintroduction because humans destroyed the dormice’s natural habitat and caused the population decline so they should restore the population. However, should animals be returned to the wild when there are still outstanding issues that led to the original decline?
Microchips are put into the necks of the released dormice which are approximately a tenth of their body length. Anaesthetic is risky for small animals and interferes with their natural state. The chips are considered important for monitoring the dormice to help with the programme. They could be eaten by a predator in the food chain and the microchip would be affecting natural processes.
If the reintroduction is not successful and the mice die this could be due to human error and animals may have suffered as a result of this.
The scheme is expensive as the release is labour intensive, with staff needed to survey the area before and after release. This diverts resources from much more cost-effective ecosystem and habitat conservation measures.
The health screening is expensive and microchips costs ï¿½8 per mouse on top of anaesthetic and vetinary bills.
The nest boxes and cages used can intrude on the natural woodland, with the possibility of dormice causing a shortage of food for the other animals in the ecosystem.
Some behaviour in genetically inherited but some is learnt from adults and experience. Captive bred animals do not gain this knowledge and are at a disadvantage when reintroduced. The mice might lose their ability to create their own nests.
The reintroduced dormice could cause a problem to the local residents.