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Published
Papers: Studies on Released Rehabilitated Hedgehogs |
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Wildpro Reference Code: J3.143.w1 Hedgehog rehabilitation in perspective P A Morris
BSc, PhD, School of Biological Sciences, Royal Holloway, Veterinary Record (1998) 143, 633-636 Field studies and methods Thousands
of hedgehogs are taken into care each year, mostly injured animals or
late-born young unlikely to survive hibernation. Many are returned to the
wild, but until recently there was little information about their welfare,
behaviour or survival after release. A review of three studies undertaken in
different regions of Britain, showed that the majority of 33 released adults
and juveniles adapted quickly to life in the wild despite the juveniles
having been raised in captivity. They found food readily, made nests and
rapidly learned their way about. They all lost weight initially but, after
two to three weeks, stabilised at a similar weight to wild animals. The
hedgehogs which were heaviest at release lost the greatest percentage of
their bodyweight, suggesting they had become overweight in captivity. The
hedgehogs which were known not to have survived at least six weeks after
release included three road casualties and three eaten by badgers. Although
wild hedgehogs may die in the same ways, it is possible that the released
hedgehogs' susceptibility to such dangers may be increased by their becoming
tame during captivity. However, the high survival rate suggests that the
release of rehabilitated hedgehogs back into the wild is worthwhile. Increasing
numbers of British hedgehogs (Erinaceus
europaeus) are taken
into care each year. One wildlife hospital claims to handle 3000 annually,
and a single private carer took in 171 during 1996 alone (M. Rhigini,
personal communication). The RSPCA treats over 1000 hedgehogs each year and
these represent an increasing proportion of all wildlife casualties treated
by the RSPCA (T. Thomas, personal communication), rising from 15 per cent in
1993 to 20 per cent in 1996. These animals consist of sick and injured
individuals, together with many late-born young which are too small to
survive hibernation (Morris 1984). Some of these hedgehogs die in captivity,
but survival rates are generally good and have improved steadily with the
increasing experience of wildlife carers.
Sainsbury
and others (1996) reported the veterinary findings from a sample of
rehabilitated hedgehogs after their release. The popular press used these
findings as the basis for articles highlighting the drawbacks of releasing
rehabilitated hedgehogs, suggesting that rehabilitation may be
counterproductive and perhaps even cruel (Daily Telegraph, December 2,
1995). The
aim of this paper is to collate the results from three follow-up studies of
rehabilitated hedgehogs and show how the information might easily be
misinterpreted unless the wider picture is properly understood. Thirty-three
hedgehogs were studied. They had been rescued from circumstances that would
have resulted in early death, cared for in captivity for many weeks, and
were destined for release irrespective of the follow-up study for which they
were later selected. They were fitted with a small radio transmitter (Biotrack)
and tracked by means of a direction-finding receiver. Their survival and
movements were monitored for a period of up to eight weeks, after which
battery life was exhausted and the transmitters had to be removed. Some
of the animals were adults with experience of living free in the wild, but
25 (76 per cent) were juveniles, selected particularly because they had
little or no experience of independent life. These juveniles had been taken
into care for various reasons, but were probably too young to have ever
built their own nest. Most had never lived alone, many had never found or
eaten natural prey and had not travelled beyond the confines of a cage. It
was presumed that if they could survive release, so would adults. Bodyweight Most
of the hedgehogs lost weight progressively for at least two weeks after
their release, but most had stabilised by about the third week. Data from 24
hedgehogs (two released in Suffolk, the rest in Devon or Jersey) which
survived more than 19 days after release and whose weights were monitored
regularly for up to seven weeks were combined. When they were released the
bodyweights of these individuals ranged from 560 to 1220 g (coefficient of
variation [CV] 18.2 per cent). Subsequently, all the
animals lost weight and the range of minimum weights recorded was 500 to 840
g (CV=12.3
per cent) as they approached a 'standard' mass. The maximum weight loss
recorded was 38 per cent and the majority lost at least 20 per cent in the
weeks after their release. The animals which lost most weight were those
which were heaviest at release. Several were more than 50 per cent heavier
than would be expected for wild hedgehogs of similar age, owing to generous
feeding in captivity and lack of exercise. The relationship between maximum
weight loss and weight at release was statistically significant (linear
regression, P<0.001, Fig 1). Nesting and orientation All
three studies showed that the released hedgehogs quickly adjusted to their
new surroundings and did not attempt to 'home' to a distant location by
heading off in a consistent direction. Typically, the hedgehogs travelled
several hundred metres in a night, comparable with distances travelled by
wild hedgehogs (Morris 1988) despite their previous confinement. They built
nests successfully and repeatedly found their way back to them again after a
night's foraging. Most re-used a previous nest (sometimes over 200 m away)
after an absence of more than two days, indicating an ability to orientate
in a new habitat. In
all three studies, after a week or more of consistent behaviour, some
hedgehogs undertook sudden, long distance movements away from the release
area. In Suffolk, half the animals travelled at least 2 km from the release
area and never returned. Two swam across the River Stour. In Devon, one
travelled 2 km then established a new regular pattern of movements, two
others dispersed 0.5 km before settling down. In the Jersey study, of the
eight animals located six weeks after release, two were still within 20 m of
the release garden, one was more than 250 m away and a ninth hedgehog was
later found alive 5.2 km from the release point. Survival and predation Pre-release cages and acclimatisation None
of the hedgehogs released in the Devon study returned to eat the food left
for them in the pre-release cages. Social behaviour
A
consistent feature of these studies was weight loss, and the large
percentage of bodyweight lost by some of the animals may, suggest that they
were unable to find sufficient food and were starving. However, the
significant (P<0.001) relationship between bodyweight at release and
maximum weight loss, indicates that these animals were shedding excess
weight put on in captivity. During
the Devon study, the nights became very wet and cold, with temperatures
around 0°C, posing an additional challenge to survival, because
invertebrates are less active in the cold. Heavy rain also threatens the
ability of homoeotherms to maintain body temperature, especially if dry
nesting sites cannot be located. It was for this reason that the animals had
not been released even earlier in the year. Some had sustained small bite
wounds in captivity (Sainsbury and others 1996), but in every case these
healed quickly after release and several of the affected animals survived
until the end of the study. There is no evidence that these minor wounds
represented a significant hazard, although it would have been better had the
animals not received them. For this reason, it seems wise to cage the
animals individually, particularly males in the breeding season, before they
are released. A
regular change of nest site is normal in wild hedgehogs, especially among
males (Reeve and Morris 1985). The released hedgehogs repeatedly found their
way back to the nests they had built and most re-used a previous nest at
least once, indicating an ability to orientate in a new habitat. Similar
results were obtained in a study of three hedgehogs released in Yorkshire
(Morris and others 1993b). Although
none of the release studies showed a consistent pattern suggestive of
'homing', several of the hedgehogs disappeared from the study areas, having
travelled considerable distances. In Jersey, at least one moved over 5 km,
and four of the Suffolk animals were last seen over 2 km from the release
point. Although these animals were 'lost' from the study, their dispersal
suggests that they had sufficient stamina to travel significant distances
and were thus probably healthy. In
Cheshire, 22 rehabilitated hedgehogs were released into a wood and radio
tracked, but all of them departed to nearby villages within two weeks (Key
1997). A similar result was obtained when hedgehogs were released into a
woodland in Surrey (N. J. Reeve, personal communication). Dispersal may be a
response to being moved to an unfamiliar type of habitat, suggesting that
hedgehogs should be released in the habitat to which they were accustomed
(Morris and others 1993a). However, in Jersey there was no statistically
significant difference between the behaviour of animals released close to
where they had first been captured and of those unfamiliar with the release
site (Morris 1997). All the animals in that study were juveniles, and were
perhaps not old enough to have become fixed in their behaviour towards their
home site before being taken into captivity. Thirty
of the 33 hedgehogs It has been argued that hedgehogs should not be released into areas frequented by badgers because of the likelihood of predation. However, the most recent published distribution map (Arnold 1993) shows that badgers are present throughout Wales and most of southern England. They occur in all but two of the 10 km grid squares between Land's End and central Wiltshire. Avoiding them, at least in the south west, is not a realistic option. Where badgers are scarce, it is often because the habitat is unsuitable, and it is frequently inadequate for hedgehogs too. Similarly, avoiding traffic is
unrealistic. Hedgehogs can travel up to 3 km in a night (Morris 1988), and
few suitable areas in the lowlands are more than 3 km from a road. The road
deaths in these studies
occurred on tiny lanes, used by very few vehicles per night. In all cases,
wild hedgehogs were already present at the release sites, irrespective of
badgers or road traffic. Drowning
is a common cause of death in hedgehogs, not because they cannot swim, but
usually because they fall into water and cannot climb steep smooth surfaces
to escape. Such mishaps are likely to occur irrespective of the animal's
health or previous life in captivity. Nevertheless, despite all these
difficulties, survival among rehabilitated hedgehogs was very high,
compared, for example, with the minimal success of oiled seabirds after they
have been cleaned and released (Schmidt 1997). A
probable risk factor is that the released hedgehogs were accustomed to being
handled. Many had been captive almost since birth and were quite tame. They
were insufficiently wary of ‘attack’ and several barely bothered to roll
up when caught for weighing each night. Tameness may increase the danger
posed by badgers and road traffic. It would therefore seem wise to
discourage tameness in animals intended for release. The
assertion that rehabilitated animals should be released in urban areas
because they will be safer there remains unsubstantiated. It may be true in
respect of predation by badgers (although badgers are common in
some suburban areas), but avoiding one hazard may simply increase
exposure to another. In the studies reviewed here, as many hedgehogs were
lost to motor traffic as to predators, despite the relative quietness of the
country lanes in the three study areas. The lanes were also narrow, slowing
the few vehicles present after dark. In urban areas, traffic will be
heavier, and persist late into the night, almost certainly increasing the
risk of accidental death. Studies
of dormice (Muscardinus avellanarius) highlight
the benefit of 'soft release' methods involving use of pre-release cages in
which the animals can become accustomed to their new environment before
release (Bright and Morris 1994). Some rehabilitators also take considerable
trouble to accustom hedgehogs to the release site before they are freed, and
provide supplementary food afterwards. There was no evidence that the
provision of food or acclimatisation to the release site through the use of
pre-release cages had any beneficial effect. A similar result was obtained
in Yorkshire (Morris and others 1993b) where none of the three released
hedgehogs returned to feed at a bowl of dog food put out for them for
several nights, despite their continuing weight losses. Nevertheless, soft
release techniques which reduce the abruptness of the transition from
captivity to the wild are unlikely to be harmful. One
of the Devon hedgehogs had defective teeth, which led to assertions that it
should not have been released without 'effective veterinary treatment'.
However, dental anomalies (including missing teeth) were found in 39 of 77
wild E europaeus (Brockie 1964) and the hedgehog released in Devon showed
no evidence of progressive weight loss that might have been expected if it
had been hampered by dental deficiencies. It lost a maximum of 21 per cent
of its weight at release, then regained much of it, and maintained its
weight stable for three weeks at 81 to 90 per cent of the initial weight,
until it was killed by a badger. The
popularity of hedgehogs ensures that relevant press stories are widely
read, and misleading reports and comments may have significant negative
effects. Articles in the press following the publication of the paper by
Sainsbury and others (1996) caused confusion among animal carers and dismay
concerning the validity of hedgehog rehabilitation. Animal careers became
concerned that dog food may be a dangerously inappropriate diet for
hedgehogs because press reporting emphasised a comment by Sainsbury and
others (1996) that eating soft dog food may lead to an accumulation of
tartar on the teeth. Claims that hedgehogs had contracted lungworm while in
care as a result of being fed on a diet of dog food instead of earthworms
were particularly misleading. In fact, earthworms are a natural source of
lungworm, Capillaria erinacei, common
in wild hedgehogs (Romashov 1980). These
studies have clearly demonstrated that released hedgehogs, even
inexperienced juveniles, coped well with life in the wild, found food,
nested normally and integrated well with resident wild hedgehogs, often in
spite of bad weather and other adverse factors. The rehabilitation of
hedgehogs is therefore a justifiable use of resources to the extent that
full integration into the wild is an achievable aim. There is no evidence
that welfare is significantly at risk, except from accidents to which all
hedgehogs are exposed. However, captive hedgehogs should not be encouraged
to become tame and unwary of potential dangers. Substantial weight loss is
to be expected after they are released, but this appears to be a natural
readjustment to weight gain in captivity. The author thanks Hugh Warwick and Louisa Gammidge for field assistance in Devon, despite inclement weather. Susan Sharafi and Kathy Meakin assisted in Suffolk; Dru Burdon, Kim Matthews, Susan Sharafi and Ruth Temple in Jersey. Mary Morris provided valuable assistance with data analysis, and Tony Sainsbury kindly read a draft of this paper. The continued support of the British Hedgehog Preservation Society is gratefully acknowledged, as is help provided by 'Pro-Igel' of Switzerland. The author is especially grateful to the RSPCA for support, and to Pete and Jean Swanston for allowing access to their farm. Arnold
H R (1993) Atlas of Mammals in Britain.
London, HMSO.
p 145 Bright
P W & Morris P A (1994)
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A W, Cunningham A A, Morris P A, Kirkwood J K & MacGregor S K (1 996) Veterinary Record 138,
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