Abstract

The main reasons for the delivery of 168 wild hedgehogs to an animal home in York, England, were investigated between 1998 and 2000. All the animals were subsequently treated at the author's hedgehog sanctuary. Of these 61% were nestlings, 25% juveniles, and 14% adults. Nestlings showed a significantly male-biased sex ratio (m:f =1.5:1), while juveniles and adults did not. However, there was significant bias (1.4:1) for all age categories combined. The degree of bias did not differ between the age categories, suggesting equal mortality in the two sexes. For all individuals combined, the most common ailments were malnutrition (27% of the animals) and dehydration (15%), while ticks (Ixodes hexagonus) (14%), nematodes (Crenosoma striatum) (11%), ringworm (4%) and sarcoptic mange (6%) also occurred regularly.

Road accidents and other injuries each affected 4%. Nestlings suffered primarily from nest disturbance, bite wounds from domestic animals, prolonged absence of the mother, and accidental entrapment. The overall survival rate was 94% and 84%, 48 hours and 20 days after admission respectively. Most nestlings (74%), juveniles (55%) and adults (58%) survived and were released back to the wild. Anthropogenic factors appear to contribute substantially to the incidence of injury and misfortune in all age groups and emphasise the need for measures directed at maintaining hedgehog populations.

Introduction

Recent population estimates (The Mammal Society 1999) of the British hedgehog (Erinaceus europaeus) indicate that the hedgehog is on the decline in England, Scotland and Wales. As the species has so far managed to survive for millions of years, early forms of the spiny hedgehog being distinct 26-38 million years ago (Reeve 1994), signs of its demise are worrying in the extreme.

The hedgehog is susceptible to a range of diseases and can sustain various injuries in suburban areas. It is also host to many intestinal parasites (Boag & Fowler 1968, Smith 1968, Majeed et al. 1989, Keymer et al. 1991). Although it is commonly reported that the most common cause of death of the hedgehog in Britain is road traffic casualties (Stocker 1987), hedgehogs can also die from many other causes (Smith 1968, Stocker 1987, Keymer et al. 1991, Reeve 1994, Sykes & Durrant 1995, Reeve & Huijser 1999, Robinson & Routh 1999).

The removal of hedgerows and small woodland fragments in agricultural areas has caused hedgehog populations to decline locally or regionally (Huijser 1999), while the mere presence of humans, with their garden ponds and strimmers, adds to the death toll each year (Reeve & Huijser 1999). However, there are many benefits to be gained by hedgehogs living in close proximity to humans, such as supplementary food, and shelter in rural and suburban outbuildings. Huijser (1999) considers that traffic mortality is unlikely to be the primary cause of a decline in hedgehog numbers, but that the way humans manage the landscape has far greater effects on the survival probability of hedgehog populations.

This study was conducted in order to shed further light on the reasons for population decline in the British hedgehog and, in so doing, to hopefully help reverse this trend. Specifically, data were collected to determine the number of hedgehogs that were heavily burdened with parasites, suffered myiasis, leg breaks, eye infections, hypothermia and other ailments, and were hit by cars. The study seeks to determine the impact of these ailments and injuries on the survival rates of hedgehogs presented initially at an animal home in York, England, then taken to the author's sanctuary, over a three year period. The animal home was run under the supervision of the Royal Society for the Prevention of Cruelty to Animals (RSPCA).

The study also attempts to establish whether seasonal variation exists in terms of different age categories arriving for treatment; whether the sex ratio differs significantly from a 1:1 null hypothesis for each category of nestlings, juveniles and adults and for all groups pooled; whether the relative survival of males and females is significantly different across the age classes, and across all categories pooled, and whether there are significant differences in survival (with the sexes combined) for the three age groups.

Material and methods

SOURCES OF DATA

For the past five years a rehabilitation programme for hedgehogs has been run at a sanctuary in York, solely by the author. The greater majority of the hedgehogs (90%, n-168, 1998-2000) presented at York RSPCA were taken to the sanctuary for the purpose of rehabilitation and eventual return of the survivors back to the wild. Records kept during the study period enabled a detailed analysis of the types of ailments and injuries that afflict displaced animals. Displaced, in this instance, refers to any hedgehog found in an exposed position in daylight hours, such behaviour often bringing it to the attention of the public. With rare exceptions, when a juvenile might appear intermittently during daylight hours due to scarcity of food in the vicinity, it is extremely rare for hedgehogs to be spotted out and about between the hours of dawn and dusk. Increased public awareness has led to a greater number of hedgehogs being taken to the RSPCA.

CODING OF AILMENTS AND INJURIES

As the aim of this study was to examine the reasons why hedgehogs had been found out in the open (displaced), and in need of treatment, their detailed assessment on arrival was crucial. All animals were weighed on arrival and assessed for signs of injury or ailment using the following categories:
1. Ringworm - Flaking or crusting of the skin, with some spine loss, accompanied by microscopic examination of skin scrapings, allowed determination of this disease (Bunnell 2000).
2. Sarcoptic mange - Often accompanying ringworm, this disease presents as tiny white flakes or dust visible amongst the spines (Sykes & Durrant 1995). The flakes are produced by the Sarcoptes mite (Sarcoptes spp.) burrowing beneath the epidermis of the skin. Mites are occasionally visible with the naked eye, and certainly by examination of skin scrapings using a light microscope (Reeve 1994). As mite infestation predisposes the hedgehog to a secondary bacterial infection, mange is often accompanied by an unpleasant smell.
3. Demodectic mange - As with sarcoptic mange, this type is also caused by a mite, in this case Demodex erinacei, which lives in the follicles of the hair or spines, resulting in hair and spine loss. Heavy infestation can lead to massive spine loss and baldness.
4. Puncture wounds - These are not always visible on initial examination as they can be obscured by the spines. Their presence often becomes evident when the resulting bacterial infection causes an abscess to form which then bursts. The presence of pus then reveals the puncture points.
5. Abscesses - These are usually present in animals that have received wounds by being attacked by a dog (or, less commonly, a cat).
6. Ticks (Ixodes hexagonus) - These external parasites are commonly present in animals that have been ill for some time and suggest a poorer prognosis. In very sick animals their removal is dealt with by the application of a safe oil (Bunnell 2001a).
7. Crenosoma striatum - This nematode is a type of lung worm.
8. Capillaria spp. - This nematode is also a lung worm.
9. Hymenolepis erinacei - This is a tape worm specific to the hedgehog and is generally detected by the presence of white segments in the faeces. Microscopic examination of faecal smears may reveal the presence of segments and eggs.
10. Isospora spp. - This internal parasite is a protozoan, infection with which is usually subclinical (Robinson & Routh 1999). However, heavy infestation can result in distinct changes to the faeces (Sykes & Durrant 1995) which appear green, watery or jelly-like, and blood-stained. Clinical signs also include weight loss.
11. Escherichia coli - This bacterium produces a watery brown diarrhoea which responds rapidly to antibiotic treatment, confirming the initial diagnosis.
12. Malnutrition - A pointed rear end and prominent ribs were two symptoms used to signify malnutrition.
13. Dehydration - When the skin was loose, with a noticeable flap where the spines meet the under fur, or when an animal moved in a wobbly, uncoordinated fashion, it was considered to be dehydrated.
14. Hypothermia - Any animal whose abdomen felt cold to the touch, that is less than 36.9 °C, was considered to be hypothermic. It was provided with an optional heat source from which it could easily remove itself. Animals incapable of movement were placed close to the heat source, but not actually on it, to avoid the possibility of overheating.
15. Breathing difficulties - These take the form of wheezing, rapid breathing, nasal discharge and often coughing.
16. Myiasis - Also known as fly strike, myiasis is detectable by the presence of tiny white clumps of blowfly eggs. These are often hidden deep within the fur and require great patience to identify and remove all of them.
17. Hit by car - Indications that a hedgehog has been hit by a car are scuffed heels (incurred when the animal is dragged or propelled along the ground), and broken spines. In addition, an animal can also sustain broken limbs and internal injuries which require immediate attention.
18. Miscellaneous injuries - These include hedgehogs becoming covered in engine oil etc.
19. Eye infection - This is indicated by the presence of discharge from the eye or eye socket, as an eye infection can often cause the eye to burst with the loss of the eye.

The presence of helminths, nematodes and protozoans in the gastrointestinal tract was determined by microscopic examination of simple faecal smear samples. In addition, overburdening by the above parasites and specific bacteria produces characteristic changes in the gross morphology and texture of the faeces (Sykes & Durrant 1995, Bunnell 2001b). Detection of large numbers (accepting that this is a relative term and subject to a margin of error) of specific parasites, accompanied by characteristic changes in gross morphology and texture of the faeces, resulted in administration of the relevant medication. Re-examination of faecal smears, within 24 - 48 hours of the hedgehog receiving medication, showed a fall in number of the relevant parasite(s), a subsequent return to normal gross morphology and texture of the faeces, and the return of normal eating habits.

AGE AND SEX DETERMINATION

For ease of identification, hedgehogs were categorised according to weight. Hedgehogs weighing under 250 g on arrival were considered to be nestlings as they needed extra care and generally a diet consisting partially of a milk substitute for puppies (in this case Esbilac^(R)), in order to gain weight at a satisfactory rate. Nestlings, ordinarily, would have still been receiving care from their mother. Animals weighing between 250 and 450g were classed as juveniles, while any over 450g were classed as adults. Data collected in this study showed that hedgehogs born in spring or summer easily achieve weights of 650 - 900g by autumn in the same year. The sex of all animals was also determined on arrival, enabling determination of sex ratios.

Arrival of all age categories of hedgehogs at the RSPCA, and later at the sanctuary, was influenced by factors such as public awareness and localised extensive flooding in York in November 2000.

Results SEASONAL VARIATION Hedgehogs arrived at the sanctuary for treatment between May and January (figure 1 at right). Adults arrived mostly in May and June, while the number of juveniles fluctuated between June and January. Nestlings appeared between June and November, peaking twice in July and October.

Figure 1. The number of nestling, juvenile and adult hedgehogs arriving for treatment during 1998, 1999 and 2000

AGE STRUCTURE AND SEX RATIO

The greatest number of displaced hedgehogs arriving during a three-year period (1998-2000), were nestlings (n=102) which displayed a male-biased sex ratio of 1.5:1 (m:f) (X²=3.921, 1 df, P less than 0.05) (Table 1). Examination of 10 individual litters (32 young in total), with a minimum of three siblings in each, showed variable sex ratios between litters, but an overall male-biased sex ratio of 1.5:1 (m:f). Juveniles and adults displayed a sex ratio of 1.1:1 (m:f) (X²=0.095, 1 df, ns), and 1.7:1 (m:f) (X²=1.50, 1 df, ns), respectively. Therefore, nestlings deviate significantly from a 1:1 ratio, while juveniles and adults do not. However, as there is no heterogeneity in the data (X²=0.849, 2 df, ns), pooling across the age categories gives 1.4:1 (m:f). This is significantly different from 1:1 (X²=4.667, 1 df, P less than 0.05).

It can be concluded therefore, that the sex ratio is significantly biased towards males, and that the degree of bias is not significantly different between nestlings, juveniles and adults. This suggests equal mortality rates in the two sexes.

INCIDENCE OF DISEASE AND INJURY

Nestlings, juveniles and adults were affected by a variety of ailments or injuries (Table 2). Malnutrition was the major ailment, 55% of these being nestlings. Of the 15% affected by dehydration, the majority were again nestlings. Hypothermia was seen mainly in nestlings and juveniles, and breathing difficulties mainly in adults. Puncture wounds were mostly accompanied by abscesses and equally distributed across the age groups.

Myiasis was only observed in three nestlings (2% of the total). Ticks were virtually absent in nestlings, being mainly prevalent in juveniles. The majority of cases of ringworm and sarcoptic mange were found in nestlings (table 2), while demodectic mange only appeared in 1% of all animals. The nematode Crenosoma striatum occurred more often than Capillaria spp. and the cestode Hymenolepis erinacei, with the latter two mainly infesting juveniles. The protozoan Isospora spp. also appeared mainly in juveniles. Escherichia coli was only detected in 1% of all animals.

Only six animals arrived with road traffic injuries (4%), while two individuals arrived with an eye infection. Two animals (1%) sustained a broken leg, and miscellaneous injuries including contamination with engine oil were seen in 4% of all arrivals.

SURVIVAL RATE

Of the nestlings, 74% survived to release status, compared with 55% of juveniles, and 58% of adults (Table 3). Then the data were further analysed to determine whether mortality is the same in males and females in the three age categories considered separately. There was no significant difference (P greater than 0.05) between survival rate of females and males in nestlings (X²=0.925, 1 df, ns), juveniles (X²= 0.423, 1 df, ns) or adults (Fisher's exact test, ns). It can be concluded that there is no evidence for differential survival between males and females within any of the three age categories. There was no difference in the proportions of males and females surviving in the three age categories (X²=1.054, 2 df, ns). Therefore, there is no evidence that the proportions of the sexes surviving differ by age. Pooling across the age categories gives a total of 50 females and 64 males surviving, meaning that 20 females and 34 males died in total. There were, however, no differences in survival rate between the sexes (X²= 0.702, 1 df, ns). Given that there are no differences in survival rate between the sexes, the male and female data for each age category can be combined in order to compare the proportions of survivors versus deaths. For nestlings, survivors number 77, deaths 25; for juveniles, survivors number 23, deaths 19; and for adults, survivors number 14 and deaths 10. There were significant differences in survival (with the sexes combined) for the three age groups (X²=7.025, 2 df, P less than 0.05). As noted earlier, nestlings had a higher survival rate than either juveniles or adults.

Figure 2. The percentage of hedgehogs (n=168) that survived a certain number of days
and the percentage released during the same period.

The vast majority (94%) of the animals was still alive 48 hours after admission (total n=168) (figure 2 above). As all animals were released to the wild as soon as they were fully rehabilitated, the data in the figure includes these animals. Figure 2 also illustrates the time spent at the sanctuary prior to release. During the 20 days following their admission, 15 animals were released and 34 died, giving a survival rate of 84% (n=153). If those animals that were rehabilitated and released after 20 days are considered in the total, the survival rate becomes 80% (168-15=153 total remaining after release). Considering all age categories, 68% of animals arriving for treatment were rehabilitated and successfully returned to the wild (figure 2 and table 3).

Discussion

SAMPLE COMPOSITION

Nestlings comprised 61%, juveniles 25%, and adults 14% of the hedgehogs arriving over the three-year study period. The number of each age category arriving throughout the year varied depending on the time of year. With the exception of a solitary animal in January, nestlings arrived between June and November, with two distinct peaks between June and August, and later in October, suggesting two breeding periods. Reeve (1994) comments that in Britain and northern Europe, late litters are common. Such litters may result from the loss of a first litter or a very mild autumn, the latter increasing food availability.

Juveniles arrived between June and January, the maximum number appearing in November, while adults arrived between May and November, the largest number being in May. The appearance of juveniles in larger numbers in the autumn corresponds to the known breeding season (Reeve 1994).

Across the age categories the sex ratio is significantly biased towards males (1.4:1). Reeve and Huijser (1999) also found an overall significant male-biased sex ratio of 1.2:1. In this study, when taking the age groups separately, the nestlings alone showed a significant male-biased sex ratio which suggests that more male hedgehogs are born than females.

REASONS FOR DISPLACEMENT

Increased awareness by the public has led to greater numbers of displaced hedgehogs being taken to wildlife rescue centres. Despite this some hedgehogs are still reported by some members of the public as appearing to be in good health when they are actually in need of care. The characteristic hyperactive behaviour of juveniles, during the day in late summer or early autumn, is almost certainly due to a heavy burden of intestinal parasites which causes intense discomfort leading to hyperactivity. This fact has been confirmed by the veterinary surgeon consulted during this study, and further verified by the fact that hyperactivity ceased within 24 hours of the animal being dosed with the relevant worming medication.

Hyperactivity, in this instance, involves excessive movement during daylight hours with a total absence of sleep. The hedgehog moves incessantly, ignoring any food offered. This type of hyperactivity is not to be confused with food-searching behaviour, which inevitably ceases once food has been located and eaten.

The main reasons for displacement of nestlings are removal from the nest by domestic animals, accidental entrapment in farm buildings, and either death of the mother due to road or other accident, or entrapment or incapacitating injury preventing her return to the nest. In any instance when a mother fails to return to the nestlings within an indeterminate period of time, the nestlings tend to move away from the safety of the nest, presumably in search of food. I have observed this on many occasions, and indeed it is the main reason for notification by the public that a litter of hedgehog babies is in need of help. People who become aware that the mother has been absent for several days are reluctant to disturb the nest, tending to wait and see if the mother returns. This is generally followed by the appearance of the young outside the nest this making them vulnerable to predators and unable to survive prior to weaning. The nestlings are then taken into care.

Of the 102 nestlings displaced, 55 were not obviously suffering from any problem other than separation from their mother at too early a stage in their lives. In these cases, rehabilitation was relatively straightforward, requiring hand-feeding at frequent intervals, and the usual care regime used for orphaned mammals (Stocker 1987, Sykes & Durrant 1995).

As most road casualties will die, either immediately or very quickly, from their injuries, they were expected not to feature strongly as a reason for presentation at the RSPCA. This did indeed prove to be the case with only six out of 168 animals (4%) arriving as road casualties.

Combining the data across the age categories, the most common ailments were malnutrition, affecting 27% of animals, and dehydration (15%). Nestlings were particularly affected by malnutrition, forming 55% of those affected, and dehydration (52%). Puncture wounds were evident in 5% of animals, mainly being sustained from dog bites. Indeed, dog bites are a well-known cause of injury to hedgehogs resulting in 2.1% of hedgehog rescue centre deaths (Reeve & Huijser 1999). Myiasis was only seen in 2% of animals, all nestlings. In each instance the animal was also suffering from hypothermia.

Ticks Ixodes hexagonus were present in 14% of animals (63% of these being juveniles). This is substantially less than the figure quoted by Smith (1968) who reported that almost every wild hedgehog caught in Europe is infected with one or more ticks. Considering that the 14% of animals infested were all casualties requiring treatment, it might be expected that healthy wild hedgehogs would be less likely to carry ticks. This suggestion is supported by data collected during this study which indicate that the number of ticks infesting a casualty seems to be directly related to its state of health and prognosis for a return to full health. Those animals possessing more than 25 ticks mostly failed to survive. The greatest number of ticks recorded between 1998 and 2000 was 72. However, a hedgehog bearing 199 ticks was treated by the author in 1997, an excessive number for such a small mammal.

Ringworm was found in 4% of all animals, though mainly in nestlings. This figure does not compare with that quoted by Morris and English (1969) where they report an average infection rate of about 20-25% in Britain, with the fungus being cultured from the linings of 23% of 60 nests examined. One possible reason for the discrepancy is that the presence of fungal spores on the spines or fur of a hedgehog, or within the nest material, does not necessarily mean that the animal will actually present symptoms of ringworm. Smith (1968) states that wild hedgehogs harbour a large number of potentially pathogenic organisms without showing visible signs of illness. Those animals that succumb to the disease generally have compromised immune systems due to an underlying illness.

Sarcoptic mange was observed in 6% of animals and was sometimes accompanied by ringworm. This is not surprising as the mites responsible for the mange could also help to spread the ringworm as the fungus has been isolated from their droppings (Reeve 1994). Demodectic mange was only observed in 2% of animals and as Reeve (1994) reports that the mite Demodex erinacei commonly inhabits the hair follicles of hedgehogs, this would suggest that it is mainly asymptomatic.

The nematode Crenosoma striatum was the parasite most commonly noted to be present in excessive numbers, with an accompanying change in the gross morphology and texture of the faeces (11% of total) (Bunnell 2001b). Infections produced by this lungworm and that of Capillaria spp. (5% of total) are commonly fatal in hedgehogs (Reeve 1994) and typically produce consolidation of the lungs as revealed during post mortem. Robinson and Routh (1999) also comment that the morbidity associated with lungworm infection can be very high. Keymer et al. (1991) found nematodes, which they considered to be probably all Crenosoma striatum, to be the most important helminth pathogens in 10 casualties, attributing their presence to be largely responsible for the death by pneumonia of six of the animals.

The tapeworm Hymenolepis erinacei was present in excessive numbers to the point of producing changes in the faeces, coughing and weight loss, in 5% of all animals. This figure is similar to the 1.2% incidence of tapeworms reported by Reeve and Huijser (1999). Robinson and Routh (1999) state that infection with the tapeworm Hymenolepis erinacei is usually asymptomatic. Escherichia coli was noted in 1% of animals. The incidence of parasite and pathogen infestation was distributed equally over the sexes.

Broken limbs, thought to have been caused by dogs, were seen in two animals only (1%), while miscellaneous injuries caused by human-related activity were observed in 4% of all animals.

SURVIVAL

Considering all age categories, 68% of animals arriving for treatment were rehabilitated and successfully returned to the wild. Out of a total of 168 animals 94% were still alive 48 hours after admission. This compares favourably with survival rates at the Jersey and Den Haag hedgehog rescue centres, where only 45.7% of admissions survived for 48 hours (Reeves & Huijser 1999). Indeed, 80% of animals were still alive 20 days after admission, making the necessary adjustments for the 15 animals released during this time.

Nestlings displayed the highest survival rate at 74%, with juveniles and adults surviving at the almost equal rates of 55% and 58% respectively. Combining male and female data the difference in survival rate between the age groups was significant. Although more females tended to survive than males, this difference was not significant, indicating equal mortality rates for both sexes in all the age categories.

Recommendations

Animals that were successfully restored to good health were returned to selected sites in the wild. Survival of rehabilitated hedgehogs, after release to the wild, has been studied (Morris et al. 1993, Morris & Warwick 1994). These studies concluded that rehabilitated adult hedgehogs probably cope well with release. This is supported by my findings (Bunnell, unpublished data), whereby several marked, rehabilitated animals from my sanctuary have been observed many months after release, mostly close to the release site. Increased awareness by the public, in recognising that hedgehogs found out during the day generally require assistance, is helping to bring more animals to the attention of wildlife rescue centres. This, in turn, increases the number of animals that receive much-needed care and attention, are subsequently rehabilitated and returned to the wild. The action of wildlife centres throughout Britain is undoubtedly ensuring the return to the wild of thousands of hedgehogs that otherwise would have perished. It is hoped that, in some small but significant way, the balance that has been severely disturbed by human habitation and interference in the life of the British hedgehog, is addressed by the care provided by wildlife rescue centres.

It is recommended that public awareness be increased still further, in particular to alert people to check buildings, basement yards, etc. where hedgehogs could accidentally become trapped and subsequently starve. In addition, it would be of great value if all cattle grids, installed prior to the law insisting on a climb-out point for hedgehogs, were to be provided with a means of escape for any hedgehog casualties. The removal of traps altogether from the countryside would prove most beneficial for the hedgehog and eliminate a prolonged death from starvation. Increased diligence by householders, to prevent domestic animals from disturbing hedgehog nests, would also be most useful in attempting to reverse the decline of hedgehog populations.

Acknowledgements

I am particularly grateful to Dr. Geoff Oxford (Department of Biology, University of York) and to Dr. Huw Griffiths (Department of Geography, University of Hull) for much appreciated discussion of the data. I would also like to thank the supervising veterinary surgeon Keith Warner (MRCVS, Minster Veterinary Practice, York), Roma Oxford (hedgehog rehabilitator), and Gordon Woodroffe, for valuable discussion and feedback relating to this study.

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The above paper was originally published in the journal LUTRA, Volume 44, Number 1, September 2001, pages 3 -14. Copyright ownership remains with the journal. Abstracts of papers published in LUTRA can be found on the following website: http://www.vzz.nl/