TECHNIQUE

Release of Casualty Erinaceus europaeus - West European Hedgehog (Mammal Husbandry & Management)

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Summary Information
Type of technique Health & Management / Hedgehogs: Health & Management / Techniques:
Synonyms and Keywords N.B. This information should be read in association with Wildlife Casualty Release which contains background information together with links to the Electronic Library and Organisations (UK Contacts). The related Species pages contain similar linkages.
Description This page has been prepared for the "UK Wildlife: First Aid and Care" and "Hedgehogs: Health & Management" Wildpro volumes, and is designed for the needs of the following species: Erinaceus europaeus - West European Hedgehog

Pre-release:

  • Some carers suggest that no pre-release preparation is required if these animals have been in care for a short period of time.
  • A period of acclimatisation in an outdoor enclosure is recommended for hedgehogs which have been in care for more than a short period Some carers suggest that all hedgehogs should be given a period of acclimatisation prior to release. See: Long Term Care of Hedgehogs (Erinaceus europaeus) 
    • Acclimatisation is recommended for five days for adults which have been in care for a short time and up to two weeks for inexperienced animals and others where there may be doubt regarding the animal being ready for immediate release. (V.w56)
    • For information on overwintering juveniles see: Over-wintering Underweight Juvenile Hedgehogs (Erinaceus europaeus)

Release assessment/criteria:

  • Released mammals:

    • Must be able to recognise, catch, manipulate, consume and digest their natural diet.
    • Must be capable of normal locomotion (movement) and have sufficient fitness for sustained activity.
    • Must have adequate sensory ability (sight, smell, hearing, touch).
    • Must be of an appropriate weight for the age, sex, and time of year. 
    • Must have a satisfactory hair coat.
    • Must show appropriate wariness of humans and domestic animals.
    (P19.1.w10, P24.233.w11, J35.147.w1, D27)
  • Appropriate health checks should be carried out prior to release. A careful assessment (risk analysis) must be made as to the risks of released animals introducing novel pathogens (disease agents) into the wild population/environment.
    • These pathogens may have been acquired from domestic animals, other wildlife casualties or humans whilst the animal was in captivity.
    • The health checks should be designed to minimise the risk that pathogens posing a threat to wild populations of this or other species will be introduced into the environment when the animal is released.
    • (V.w5, V.w6, P28.2000.w1, J15.20.w3)
Hedgehog-specific criteria:
  • Hedgehogs should always be released unless disabled.
  • Hedgehogs must be able to roll up tightly, and have a full coat of prickles, when they are released.
  • Hedgehogs have a particularly high incidence of periodontal disease. A dental examination under general anaesthesia may be appropriate with cleaning and treatment as required prior to release.(B151, V.w26)
  • Consider having a blood sample evaluated for detection of problems not visible by physical examination.(B151)
  • Consider providing natural food items as part of the diet prior to release. (D78)
  • Weigh before releasing. Hedgehogs require sufficient energy (fat) reserves if they are to survive hibernation. Suggested minimum release weights are:
    • Mid-summer: 450g, to end November, 500g, to middle of December, 600g. (B151)
    • Minimum 600g (1 1/2 lb) in autumn for juveniles. (D78, B337.2.w2)
    • Note that an adult weighing only 600g would be very thin and would be unlikely to have sufficient fat reserves for hibernation. 
  • DO NOT RELEASE IF:
    • Severely disabled, unable to curl up properly or lacking a full coat of spines. 
    • Less than eight weeks old.
    • Weight is less than 600g and the hedgehog will need to hibernate soon.
    • (B337.2.w2, B337.4.w4)

Timing of release:

  • Hedgehogs should be released in the evening (at dusk or just after dark). (B151, B199, B337.2.w2, , B337.4.w4, D52, D106)

  • Mild evenings are best for release. (D106)

  • Warm damp weather is preferable in summer as more food (e.g. earthworms) will be available than during dry weather.(D78)

  • It has been suggested that hedgehogs should not be released between mid-December and mid-April. (B151)
  • If releasing in winter then mild weather is best; a time without snow and without severe frost must be chosen. (D78)
  • Hedgehogs may be better overwintered in a safe area with appropriate hibernation facilities than released in winter when finding an appropriate place may be difficult.
    • It has been suggested that overwintered animals becoming active before late March and weighing more than 700g should be fed only minimally, encouraging resumption of hibernation. This reduces the risk that they will become sexually active too early and become restless in captivity, as well as reducing the risk of obesity. (J147.3.w1)
  • In spring hedgehogs should not be released until wild hedgehogs in the area are known to be active and invertebrate prey items (e.g. worms, slugs, beetles) are active at night. (J147.3.w1)
  • DO NOT RELEASE in frosty or drought conditions, when the ground is very hard, or when it is very wet and the released animal may have problems finding dry bedding to make its nest. (B337.2.w2, , B337.4.w4)

Selecting a release site:

  • If the site of origin is known and is suitable (NOT e.g. a main road), the hedgehog should be released back to the same place. (D106)
  • In suitable habitat as suggested by the presence of other hedgehogs.
    • e.g. in deciduous woodland or with access to 10 or more gardens.
    • Pastureland, moist deciduous woodland, large cemeteries and areas with gardens are good sites. (D78)
    • The area must provide suitable nesting materials (fallen leaves) and sites for nest construction (hedges, brambles or similar). (D78)
    • Avoid repeated releases at the same site. (B337.2.w2)
    • Releasing back into the area of origin reduced the risk of the hedgehog encountering a new disease, or of introducing a disease into the release area which was not there previously
  • Release sites should be of a similar habitat type to that in which the individual was found e.g. suburban hedgehog released back to suburban not rural area.(V.w5)
  • Away from major roads (e.g. "A" and "B" roads) and busy railway lines as far as possible.
  • (B151, B156.7.w7, B224, B337.2.w2, B337.4.w4, B337.4.w4, D78, D106)
  • If a lactating female is presented as a casualty but its condition is not serious, release at the site of origin within 24 hours has been suggested so that the female may return to her litter.(B151)
  • The site of release should be recorded clearly (e.g. street name and house number, Ordnance Survey map reference if possible).
  • For release of a litter of hand-reared hedgehogs it has been suggested that the chance of most of the animals immediately dispersing may be reduced if only one individual is released at any one site. (B337.2.w2)
  • UNSUITABLE sites include:
    • There are no other hedgehogs present: there will be a reason why apparently suitable habitat is not actually suitable.
    • There is already a very heavy hedgehog population.
    • Gardens in the vicinity are known to contain dangerous dogs, use molluscicides or have ponds without hedgehog escape ladders present.
    • A badger colony or other predators are known to be nearby. 
    • It is fully enclosed (e.g. a walled garden) and the hedgehog cannot easily leave, as there may be insufficient food available.
    • An island, as this may not provide enough food and introduced hedgehogs on islands can upset the natural balance of life on the island. 
    • The ground is waterlogged or likely to become so in winter. (D78)
  • (B151, B156.7.w7, B224, B337.2.w2, , B337.4.w4, B337.4.w4, D78, D106)

Type of release:

Hard release:

  • Hard release techniques are normally used for adult hedgehogs.
  • Release in the evening.
  • Release under a hedge for cover.
  • May be released via a suitable nest box (or e.g. a sack of hay), leaving the box for use by the hedgehog.
  • May be marked prior to release, using methods such as paint, shrink-fitted plastic tubing, or ear tag.
  • (B151, B199, D78, D106)

Soft release:

  • For hand-reared juveniles supplementary food should be provided following release; this may also be provided for adults.
  • A box with suitable bedding should be left at the release site providing shelter for the hedgehog.
  • Release at dusk to give the hedgehog the whole night for exploring and finding food.
  • Continue providing food until the hedgehog stops returning (individual marking e.g. with coloured markers on spines is required to identify that the hedgehog eating the food is the one just released).
  • Food can be protected from cats by being offered under an upturned plastic box, weighted with a stone or brick and with a hole in one side sufficiently large for the hedgehog to enter and leave comfortably.
  • (B337.2.w2, B337.4.w4, D52, D78, D106)

Monitoring after Release:

In order to allow monitoring after release the hedgehog needs to be marked, for example by paining spines with quick-drying non-toxic paint, sticking coloured beads to the spines, or using ear tags.(B337.4.w4)

Results of Release Studies:

Several studies have been carried out regarding post-release survival and/or behaviour of hedgehogs. Very useful data has been obtained from radio-tracking studies. Data has also been obtained from sightings of hedgehogs marked prior to release. (P37.2.w1)

  • Studies involving colour-coded pvc tubing on spines have shown survivorship up to five years in Dresden. (P37.2.w1)
  • On Jersey (Channel Islands, UK) hedgehogs have been marked with ear tags prior to release and monitored on an ad-hoc basis by chance sightings of hedgehogs in the wild (alive or dead) and by re-admission to the rescue centre at a later date. Survival of at least five years has been recorded. (V.w56)
  • A pilot study involved four hedgehogs fitted with radio transmitters and released into an area known to provide good hedgehog habitat (Malham in Yorkshire, UK). The release took place during dry weather when food availability may not have been optimal. One male became lethargic after release and died just six days after release; the reasons for the death were unclear. The other animals showed an ability to build and return to nests, travelled distances comparable with wild hedgehogs in similar (woodland) habitat (females (no. 225 and 255) about 500m per night, over about three hectares, male (no. 275) average 795 m per night, over about six hectares). The range used did not increase greatly after the first seven nights although some new areas were explored. All three were observed foraging and locating natural food, however the male lost 100g (compared to weight of 1kg 24 hours post release) while the females lost 6% of 760g (no. 225) and 35% of 685g (no.255) respectively. None of the hedgehogs used dog food provided at the release site. The male was observed courting wild females and spent a considerable amount of time in this activity. When after 13 nights the females were moved more than 0.5 km to sheep pasture, their nightly travels increased. Female no. 225 moved back, overnight in unfamiliar territory, to near her previous location and when moved again returned once more, directly to her original nest. Female no. 255 wandered more and was last seen in a small plantation area, with a male hedgehog. (P13.3.w1)
  • Eight rehabilitated adult hedgehogs were released onto farmland, in an area known to support hedgehogs, in warm dry weather (not sufficiently dry to cause food shortages). The hedgehogs were monitored closely for the first three weeks then four weeks later were followed up. One animal became ill and died, possibly indicating premature release. One animal became entangled (transmitter caught on grass and brambles) and was fly-stuck, but was rescued, cleaned and re-released. The hedgehogs tended to lose a little weight initially then maintain or gain weight slightly. By the end of the first three weeks seven animals were still alive. Normal behaviours were noted such as courting, nest building, returning to a previously used nest and establishing a home range. There were no aggressive interactions noted with resident hedgehogs. Most scattered from the release site. At least six were still alive after five weeks. At least three were still alive after seven weeks and had gained weight. and a probably three others were reported by members of the public at sites 2- 4km from the release site. By eight weeks in addition to the one which died from illness one had drowned and another been killed by a car; one was known to be still alive and four were unaccounted for; it was considered unlikely all were dead. (J147.2.w1)
  • Twelve juvenile hedgehogs, with little or no experience of life in the wild before being rescued, were released in pasture land in Devon and monitored nightly for five weeks. Six were "hard released" and six "soft released" after five nights in small cages at the edges of the fields. Three made dispersal movements after several nights. Substantial weight loss (e.g. 20-30%) occurred initially, particularly in the heaviest (overweight) animals; weights stabilised after about one month. Animals rapidly learnt their way about the area, foraged effectively on natural foods, built nests and returned to them and interacted with other hedgehogs. Three females were found to be pregnant 26-49 days after release. One animal was euthanased after 17 days due to illness, three were predated by badgers after surviving for five weeks and two was killed by cars after five days and four weeks respectively. Four were known to survive to the end of the study and two until their radios were lost after three and four weeks. The study was interpreted as showing that juveniles without previous experience could survive after release. The hedgehogs did not show regular use of the pre-release cages after release. (J147.3.w1)
    • Pre-release health checks in these animals revealed problems of periodontal disease and bite injuries from other hedgehogs. The animal euthanased 17 days after release had parasitic bronchitis, verminous gastroenteritis and chronic interstitial nephritis. One animal had died while anaesthetised prior to release; it was found to have chronic lung abscessation, bronchopneumonia and chronic low-grade myocarditis. The hedgehog killed by a car four weeks after release had shown weight loss; on necropsy it lacked subcutaneous or abdominal fat and its stomach was empty; failure to thrive may have increased its chance of being run over. Animals were overweight prior to release; this may give a "buffer" during the period after release when learning to forage effectively. There was no evidence that the release caused adverse effects in the local wild hedgehog population. (J3.138.w2)
  • A study involving eight rehabilitated hedgehogs released into a reserve found that six of the hedgehogs were lost within a week, mainly or totally due to predation by foxes. This study showed that the site, although apparently suitable habitat, was not an appropriate release site. A different site was then chosen and further radio-tracking studies found that all hedgehogs which were successfully tracked survived for the two-month period of the study. (N6.33.w1)
Appropriate Use (?)
  • Hedgehogs should always be released unless permanently disabled by injury, in which case sheltered accommodation may be appropriate: See: Long Term Care of Hedgehogs (Erinaceus europaeus)
  • Hard release is most appropriate for animals which have been held in captivity for only a short time, for adult animals and for animals being released back into their own territory.
  • Soft release with provision of supplementary food is most suitable for hand-reared juveniles.
  • The individual animal must, at the time of release, be healthy, have a reasonable level of fitness and be able to fend for itself in the wild.
Notes
  • This nocturnal/crepuscular species should be released at night.
  • Release should preferably take place during a period of fine weather.
  • Hedgehog rehabilitators may find it useful to keep a list of individuals who are prepared to release hedgehogs in their garden or nearby, and to provide food following release. (D52)
Complications/ Limitations / Risk
  • Hedgehogs have a particularly high incidence of periodontal disease. A dental examination under general anaesthesia, with cleaning and treatment as required, may be appropriate prior to release.(V.w26)
  • Hedgehogs should not be kept as pets.
  • Hedgehogs are unlikely to survive if underweight at the time of release. Such individuals may need to be kept in warm conditions and not hibernated. See: Over-wintering Underweight Juvenile Hedgehogs (Erinaceus europaeus)
  • Hedgehogs may be better overwintered in a safe area with appropriate hibernation facilities than released in winter when finding an appropriate place may be difficult.
  • Enclosed or walled gardens which the hedgehog cannot easily leave are not suitable as release sites as they will not contain sufficient food for the hedgehog. However such sites may be suitable for disabled hedgehogs requiring long term care, or as a "half way" habitat prior to release. See: Long Term Care of Hedgehogs (Erinaceus europaeus)
  • Islands which do not have hedgehogs living on them already are not suitable release sites: the habitat may not be appropriate, food may not be sufficient and the hedgehog may adversely affect other species already living on the island. 
  • Released animals may be at risk of contracting disease if there is an ongoing disease problem in the wild population at the time of release.
  • The wild population may be at risk from novel pathogens (disease agents) carried by a rehabilitated animal. These pathogens may pose the greatest threat to free-ranging populations if the animal is to be released at a site distant from its original location therefore increasing the likelihood of spread of disease. It is important to remember that the casualty wild animal may have acquired disease from domestic animals, other wildlife casualties or humans whilst in captivity. 
Equipment / Chemicals required and Suppliers
Expertise level / Ease of Use
  • No particular expertise required.
Cost/ Availability
  • Soft release may involve a considerable time investment.
  • Soft release may be expensive in terms of construction of appropriate temporary accommodation at the release site.
  • Costs of appropriate health screening.
Legal and Ethical Considerations
  • The potential risks to the individual being released and to the wild population into which it is being released (also to domestic animals) must be considered before release is undertaken.
  • The potential risk to humans and pets from habituated/tame individuals must be considered.
  • An offence may be committed under Section 1 of the Abandonment of Animals Act 1960 if a released rehabilitated animal does not have a reasonable chance of survival (i.e. a chance similar to its non-rehabilitated peers). 
    • This may include release at an unsuitable site, in the wrong territory, unfit, not having learned to hunt, at the wrong time of year etc. 
  • (J35.147.w1, B156.21.w21, B223, W5.Jan01)
  • If releasing not onto your own land make sure that the owner has granted permission for you to release. (B337.2.w2, , B337.4.w4)
  • Check that no studies are underway (e.g. on a nature reserve) which your release may interfere with. (B337.2.w2, , B337.4.w4)
  • N.B. Information on this page should be read in association with Wildlife Casualty Release (with special reference to UK Wildlife) which contains background information on release considerations for all species.
  • See: Wildlife Casualty Legislation (with special reference to UK Wildlife) for further information on relevant legislation.
Author Debra Bourne (V.w5)
Referee Becki Lawson (V.w26); Suzanne I. Boardman (V.w6); Kay Bullen (V.w45); Dru Burdon (V.w56)
References

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