Italian Journal of Zoology, September 2006; 73(3): 227–235
Reintroduction of the Eurasian badger (Meles meles) in a protected area of northern Italy
ALESSANDRO BALESTRIERI, LUIGI REMONTI & CLAUDIO PRIGIONI* Dipartimento di Biologia Animale, Universita` degli Studi di Pavia, Pavia, Italy (Received 21 July 2005; accepted 19 January 2006)
Abstract Between 2001 and 2004, with the aim of restoring the natural biodiversity of a protected area, the Eurasian badger (Meles meles) was reintroduced into the Montevecchia and Curone Valley Regional Park (northern Italy), where it had been extirpated by human persecution. The project was combined with the reduction of badger damage on railway tracks allowing at least a pair of badgers per year and to move animals whose translocation would have been anyhow imposed by precautionary measures. Four badger family groups (a total of 12 animals) were trapped and moved to an acclimatisation enclosure located in the middle of the release area. Post-release monitoring was carried out by both radio-tracking and indirect methods. The average group range size (1.58 km2) was similar to reports from favourable districts in Britain, supporting the contention that badgers can thrive in this area. Radio-tracked badgers selected woods, while urban areas and cultivated field were avoided. Although results indicate that the badger has actually established in the Park, with badger field signs currently spread on 40% of the protected area, more monitoring is needed to determine whether it is at sustainable levels or if more translocation should be considered.
Keywords: Eurasian badger, northern Italy, reintroduction, wildlife management
Introduction Carnivores, being at the top of the food chain, play a fundamental role in ecosystem interactions and are particularly vulnerable to environmental alterations, such as habitat fragmentation, human disturbance and loss of biodiversity. As a consequence of these changes and also of age-old persecution, many carnivore species have almost disappeared in wide areas of their range (Soule´ 1995; Vitousek et al. 1997; Miller et al. 1999). However, their preservation can have positive effects on the entire system (Miller et al. 1999). Despite this, reintroductions are not a commonly used tool in Europe (Sjo¨a˚nsen 1996; Arquillie`re 1998; Breitenmoser et al. 1998; Blomqvist et al. 2000; Mustoni et al. 2003), compared to, for example, the United States of America and Canada (Griffith et al. 1989). The disproportionate difficulty of re-establishing viable carnivore populations (Griffith et al. 1989), together with the social challenges involved, and the logistic
and financial engagement needed (Reading & Clark 1996), can cause serious problems when trying to develop this management strategy. The Eurasian badger (Meles meles Linnaeus, 1758) is widespread throughout Europe (Prigioni 1999), reaching particularly high densities in the United Kingdom (Thornton 1988; O’Corry-Crowe et al. 1993; Feore & Montgomery 1999; Macdonald & Newman 2002). Thanks to its ecological plasticity, the species can occupy a variety of habitats, from Mediterranean coastal areas (Ciampalini & Lovari 1985; Rodriguez et al. 1996; Revilla & Palomares 2002; Rosalino et al. 2005) to mountainous habitats (Lucherini & Crema 1995; Virgo´s & Casanovas 1999; Prigioni & Deflorian 2005) and suburban areas (Harris 1984; Harris & Cresswell 1987; Tavecchia 1995). In Italy, the badger is relatively common over the whole mainland peninsula, but absent from Sicily and Sardinia (Spagnesi & De Marinis 2002). As a consequence, it does not need any conservation
*Correspondence: Claudio Prigioni, Dipartimento di Biologia Animale, Universita` degli Studi di Pavia, Piazza Botta 9, 27100 Pavia, Italy. Tel: 0382 986304. Email:
[email protected] ISSN 1125-0003 print/ISSN 1748-5851 online # 2006 Unione Zoologica Italiana DOI: 10.1080/11250000600679603
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management, and translocation projects designed to enhance the long-term survival of the species are not justified. Nevertheless, as a result of pest control, together with extensive urbanisation, badger distribution is not homogeneous and this mustelid can still be absent from relatively small, isolated, natural areas. To re-establish a viable population in these areas, with guaranteed protection measures in place, can represent a sound example of wildlife management aimed at the restoration of natural biodiversity and the promotion of conservation awareness (IUCN 1995). In this paper, we describe the reintroduction of the badger in the Regional Park of Montevecchia and Curone Valley (Lombardy, northern Italy), performed between 2001 and 2004. In accordance with IUCN (1995) guidelines, the reintroduction was preceded by a feasibility study, to highlight the main factors related to the disappearance of badgers and the likelihood of a natural re-colonisation of the protected area (Balestrieri & Remonti 2000a; Balestrieri et al. 2001). The study ascertained that the species had disappeared during the first half of the 1980s, when the area was managed to increase the output of game species. Badgers rarely prey upon pheasants or hares, but when extensive predator control is carried out, they are often killed in their setts by fox hunters. Actually, the protection afforded by the Park over the last 10 years has limited human pressure on wildlife. Food availability, particularly earthworms (Kruuk & Parish 1981; Kowalczyjk et al. 2000) and the presence of suitable sites for sett excavation (Neal & Roper 1991; Doncaster & Woodroffe 1993; Roper 1993) are thought to be the limiting resources affecting badger density, group and territory size. In northern Italy, maize, fruits and invertebrates form the bulk of badgers’ diet (Kruuk & de Kock 1981; Prigioni et al. 1988; Lucherini & Crema 1995; Biancardi et al. 1995; Balestrieri et al. 2004). Samples analysed for earthworm presence (handsorting 30630630 cm soil samples; Svendsen 1955; Thomson 1974) from different habitat types throughout the Park showed a higher availability of this resource in pastures (n518, mean¡SD5403¡218 kg ha21) and, secondarily, in wet woods (n519; mean¡SD5136¡165 kg ha21), while cultivated areas sustained few or no earthworms. On the whole, earthworm density was lower than in the British Isles (Edwards & Bohlen 1996), but similar to that reported for north Italian lowland and hill habitats populated by badgers (Prigioni, unpublished data). In summer various
succulent fruits are obtainable at woodland margins, in small orchards or domestic gardens. Maize is widespread in cultivated fields, and mixed deciduous forests provide plenty of chestnut and acorn. Soil composition influences sett-site choice (Dunwell & Killingley 1969; Kruuk 1978). Sandy soils are preferred (Clements 1974), while gravelly soils are avoided (Balestrieri & Remonti 2000b), probably because they are not sufficiently cohesive. Soil samples (n520) randomly collected in the Park showed less than 2% gravel. In limestone districts, such as the northern portion of the release area, badgers make use of natural fissures and caves and they are able to find and exploit soft strata (Neal & Cheeseman 1996). Some ancient setts found in the Curone Valley confirmed the use of natural small caves. On the whole, environmental characteristics appeared to be adequate to sustain a viable badger population, particularly in the central and northern portion of the Park. Nevertheless, the isolation of the protected area, together with low badger densities in surrounding hills (see the section on Release area), was considered to be a serious obstacle to natural re-colonisation. Considering that the reintroduction mainly aimed to restore a popular species into a protected area, together with the ethical questions raised by the need of finding a suitable release stock of wild badgers, the reintroduction project was performed in parallel with the reduction of badger damage on railway embankments, which allowed us to translocate ‘‘nuisance’’ animals (Linnell et al. 1997). Badger capture, acclimatisation and post-release monitoring are discussed.
Materials and methods Study area The Montevecchia and Curone Valley Regional Park is located in northern Italy, about 30 km north of Milan. It is approximately 23.6 km2 in area, with altitude ranging from 200 to 550 m a.s.l. The protected area represents a typical hilly, pre-alpine habitat, with deciduous mixed forests (about 30% of the total surface), pastures and farmlands. Woodlands are mainly dominated by chestnut (Castanea sativa) and oak (Quercus petraea, Q. peduncolata) associated with Ostria carpinifolia and Fraxinus ornus in xeric sites, to Fraxinus excelsior and Alnus sp., in hydric sites. Black locust (Robinia pseudoacacia) is prevalent in altered spots. Lower
Badger reintroduction elevations are mainly cultivated for maize and wheat or managed as pastures. The Park has little urbanisation, particularly in the northern and central parts, where woods prevail. Being on the border of intensively urbanised lowlands, the protected hills represent a sort of natural island, surrounded, particularly southwards, by a landscape extensively modified by anthropogenic development. Moreover, the badger is absent or rare on the hills which rise to the north of the Park (at least within a range of 10 km; Balestrieri & Remonti 2000a), making the more immediate recolonisation of the protected area highly improbable. Choice of the release stock Many authors have pointed out that wild-born animals are preferable to captive-born animals for translocations (Griffith et al. 1989; IUCN 1995; Sjo¨a˚nsen 1996), but the choice of a suitable capture site, especially if carnivores are involved, is not an easy task (Harris et al. 1990; Miller et al. 1999). Badger numbers in northern Italy are not comparable with those of the UK: in lowland habitats the average sett density is 0.18 setts km22 (Prigioni et al. 2001), and we do not have data to infer the effect of removals on the genetics and demographics of the source population. As a consequence, and considering also that translocations increase average mortality (Logan et al. 1996), the identification of a suitable release stock provokes practical as well as ethical questions. In these terms, the question of removing source animals without causing negative effects to the donor population put a serious restriction to the reintroduction project. Badgers generally cause only modest damage to human activities. In particular conditions, however, badger setts can be dug in the sides of artificial slopes, such as road and railway embankments or flood levees, causing lack of stability, with obvious risks for human safety. Italian northern lowlands offer relatively few suitable sett sites and this kind of damage is rather frequent along overhead railways. When alternate sett sites are available, badgers can be safely excluded from their setts and the embankment is immediately covered with a chain link fence to avoid further recolonisations (Balestrieri & Remonti 2000b). Unfortunately, sometimes artificial slopes represent the only or most available site for digging setts and the translocation of the animals living there is recommended to minimise the probability of a rapid re-colonisation. A careful selection of the release site
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is imperative: main criteria to be considered have been listed by Harris et al. (1990) and do not substantially differ from those tested by a comprehensive feasibility study. With these considerations in mind, we instigated a collaboration with the Italian Railways in order to work with animals whose translocation would have been required as a precaution to ensure railway track safety. Badger capture and transportation Badgers were captured using snares provided with a lock to prevent the total tightening of the running knot. These were checked every day in the early morning and proved selective and safe. The capture effort was 1700 nights/snare, with the simultaneous deployment of 10–12 snares. Badgers were anaesthetised with 10 mg kg21 of body weight of a mixture of tiletamina clorhydrate and zolazepam clorhydrate (Zoletil 100), administered by an intramuscular injection, and fitted with a radio-collar (collar lifeexpectancy: 18 months; frequency of transmission: 173.000–173.999 MHz). The weight of the radio (60g, corresponding to 0.6–0.7% of the badger’s body weight) prevented changes in the behaviour of the animals (Gales et al. 1990; Laurenson & Caro 1994; Cypher 1997; Bekoff 2000). Age was estimated by teeth consumption (Stubbe 1973; Hancox 1988; Harris et al. 1992). The health status of the animals was checked only by an external examination. Badgers were immediately transported to the release area (about one hour’s drive) using a cylindrical plastic cage (80 cm650 cm diameter) to reduce the potential for them to harm themselves. Badgers are protected by the Italian Law (no. 157, 11/02/1992). Their translocation to prevent threats to human safety falls within the management aspects provided for by article 19, which allows the regional authorities to deal with problems caused by wild animals within their jurisdiction. All planned measures must be authorised by the National Office for wild fauna (INFS). Neither sett protection, nor a ‘‘close season’’ (i.e. a period during which no action deterring badgers from entering their setts should be licensed; Harris et al. 1990) are provided for by the Italian legislation. In spite of juridical inadequacies, railwaymen were informed of the ecological constraints they had to consider dealing with badgers. Nevertheless, the presence of critical damage caused by badger setts was always detected in winter and, in order to allow urgent restoration, trapping sessions had to be
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carried out, with the authorities licence, mainly between January and March. Acclimatisation and release Site fidelity and territoriality are important behavioural traits affecting reintroductions. Carnivores often show homing behaviour and move excessively from the release area, negating, in practice, the prospects of success (Linnell et al. 1997). Badgers are quite territorial (Kruuk 1978; Revilla & Palomares 2002) and cannot be easily turned out of their setts (Harris et al. 1990; Roper et al. 1991; Neal & Cheeseman 1996). Post-release movement distances were a particularly serious uncertainty in our reintroduction project, due to the relatively small area of the park. To cut off the tie which connects the animals to their own territory and to encourage the development of a new enduring bond with the reintroduction area, a period of acclimatisation in a special enclosure is considered useful for many species (Linnell et al. 1997). Before their release, badgers were placed in an enclosure of 350 m2 located in a wooded area near the centre of the park, away from visitors’ paths. The surrounding valley of the River Curone comprised woods (51.5%), pasture (27.6%), and cultivated and urbanised areas in almost equal proportions (respectively, 9.3% and 11.6%). The enclosure was made of a chain link fence 180 cm high and buried 50 cm into the ground to prevent the badgers digging under it (Harris et al. 1990). Two shelters were dug 50– 60 cm into the hillside to induce badgers to excavate a sett, while fallen trees and brambles provided cover. Badgers were provisioned with maize, fruits and flesh. In 2002 and 2003, three badgers (F3, F4, F5) succeeded in climbing over the fence after a few days of captivity and, as a consequence, the size of the enclosure was doubled and the fence was provided with an overhang. When present in the enclosure, badgers were watched from a vantage point twice a week, at twilight and in the first hours of the night, using image intensifiers.
the Minimum Convex Polygon (Mohr 1947) with 100% of locations. The maximum distance recorded between two consecutive nocturnal locations (1.4 km) was considered enough to assure the statistical independence of the observations (White & Garrot 1990). The locations of each animal were assigned to the habitat type in which they occurred. Four habitats were considered: woods, pastures, cultivated fields (mainly maize and wheat) and urban areas. The x2 test was performed to test for the goodness of fit of utilised habitat to available habitat types (White & Garrot 1990). The Yates correction, suggested when the total number of observations is less than 100, was applied (Yates 1934). The expected frequencies were calculated referring to the percent cover of each habitat in each badger home range. To determine whether a habitat was selected or avoided the Bonferroni confidence intervals for the proportion of use of each habitat were checked (Neu et al. 1974). Badger ranges were surveyed monthly to locate latrines. Faecal samples were analysed according to Kruuk & Parish (1981) and Prigioni (1991); earthworms’ relative volume was assessed according to Balestrieri et al. (2004).
Results and discussion Releases From March 2001 to May 2004, badgers were trapped at four setts of as many localities; two pairs of adults (in 2001 and 2003) and two groups (in 2002 and 2004), formed by one adult male and three adult females, were trapped, giving a total of 12 animals (Table I). None showed signs of poor nutritional condition and few ectoparasites (fleas and ticks) were found. In 2001, a lactating sow (F1) was trapped. Its sett was dug and three one-month cubs were delivered to their mother in the acclimatisation enclosure. They were not, however, suckled and died. In 2002, a female (F2) was caught before parturition and birth occurred in the acclimatisation enclosure. In the
Post-release survey Badger survival and movements were monitored by radio-telemetry and periodical field-sign surveys. One day per week badgers were located, every two hours between sunset and sunrise, by triangulation of 2–3 bearings taken from a vehicle-mounted receiving system usually standing less than 500 m from the animals. Home ranges were estimated by
Table I. Badger groups composition (M5male; F5female). Year 2001 2002 2003 2004
Group composition M1; M2; M3; M4;
F1 F2, F3, F4 F5 F6, F7, F8
Badger reintroduction following years, females did not show signs of pregnancy at capture time. Genetic relationship among released animals can strongly influence the reintroduction success (Tepleton 1990). Maximising genetic diversity in order to reduce inbreeding depression is considered the best strategy (Miller et al. 1999). In trapping and moving all the inhabitants of a sett, we always dealt with naturally related animals, so preventing the social tensions that can arise when unfamiliar animals are gathered artificially. The distance of trap sites from the release area (20–40 km) minimised genetic incompatibility with badgers inhabiting the Park surroundings (Harris et al. 1990), while the distance among successive trap sites (at least 15 km) reduced the chance of releasing closely related groups. Acclimatisation time allowed us to check the badgers’ physical condition and behaviour before release. In the first days, the animals moved with difficulty under the bramble cover, until they developed well-marked paths. Latrines were dug in considerable numbers in 2002, by the pregnant female, and 2004, when four animals were gathered simultaneously into the enclosure. The analysis of their faeces (n540) revealed they had successfully foraged for earthworms, while maize was the preferred of the supplied food. Our aim was to get all the animals of a group into the enclosure before release, in order to favour group cohesion and to limit erratic movements, so, apart from escaped badgers (see methods), acclimatisation time was variable, lasting from 3 to 10 weeks. In spite of confinement, neither aggressive behaviour nor bites or wounds were recorded. Badgers movements, home range and diet in the release area Two of the escaped badgers (F3, F4) soon moved away from the release area and became untraceable. The male trapped in 2002 (M2) died soon after release, but was too decomposed to determine the cause of death. Three females (F6, F7 and F8) were
equipped with defective transmitters and their subsequent movements could not be monitored. Nine badgers were radio-tracked until two lost their collars, the radio transmitters became damaged or their battery life was discharged (Table II). The first pair of badgers (M1 and F1) found shelter in an abandoned courtyard overrun by brambles and dug a three-hole sett near a pond at the beginning of the following autumn. Progressively, seven more entrances were added. Human disturbance in the birth period probably compromised reproduction and the sett was abandoned. In 2002, the pregnant female (F2) took refuge in a natural cave; infra-red night shots were unable to pinpoint the presence of cubs. In 2003, M3 was released a few days after F5 escaped and simultaneous monitoring allowed us to attest the overlap of their activity areas. They became established in the same area as the first pair and were still present when the last group was released. Unexpectedly, these animals soon occupied the large sett dug in 2001 and successively built a new sett from some concrete pipes where, in February 2005, they successfully bred. Landscape morphology made radio-tracking difficult, so much so that field signs often helped us to make out badgers movements and to check the presence of individuals which could no longer be monitored by radio-telemetry. The home range size of M1, F2 and M4, which were radio-tracked for about nine months, ranged between 118 and 197 ha (Table II). Even if these range sizes have to be considered approximate, because of the few number of locations, they look similar to those reported for some favourable districts of Britain (21–107 ha, Kruuk 1978; 183 ha, Kruuk & Parish 1981). In northern Italian lowlands or in Mediterranean dry habitats home range size is usually larger (Rodriguez et al. 1996; Revilla & Palomares 2002; Rosalino et al. 2004; Remonti et al. 2006). The use of different habitat types significantly differed from their relative availability (M1:x32510.4, P50.01; F2: x3259.4, P50.02; M4: x3258.31 P50.03): during their night activity
Table II. Home range size of radio-collared badgers. Badgers M1 F1 F2 F4 M3 F5 M4
Radio tracking months March 2001–December 2001 April 2001–May 2001 February 2002–October 2002 March 2002–April 2002 March 2003–June 2003 February 2003–March 2003 May 2004–January 2005
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No. of locations
MCP 100% (ha)
60 13 55 8 13 4 58
197 – 159 – – – 118
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Table III. Habitat selection of radio-tracked badgers (* P,0.05; ** P,0.01). M1 Habitats Woods Pastures Cultivated fields Urban areas
F2
M4
Availability
Use
Availability
Use
Availability
Use
0.42 0.31 0.11 0.16
0.58* 0.32 0.08 0.02**
0.65 0.23 0.06 0.06
0.85** 0.14 0.00 0.00
0.58 0.13 0.23 0.05
0.74* 0.17 0.10** 0.02
all badgers selected woods (Table III), confirming the results of many researches both in high-density (Thornton 1988; O’Corry-Crowe et al. 1993; Neal & Cheeseman 1996) and low-density areas (Virgos & Casanovas, 1999; Revilla et al. 2001). Urban areas and cultivated fields were avoided. Currently, badger field signs are spread on an area of about 10 km2, corresponding to 40% of the protected area (Figure 1). Between June 2004 and February 2005, a total of 82 faecal samples (summer: 6; autumn: 22, winter: 54) were analysed. Earthworms (F%570.7%; V%554.7), maize (F%553.7%; V%566.1) and wild fruits (F%524.4%; V%558.0) constituted the bulk of badger diet in the park. Small mammals (F%57.3%; V%558.3; rodents, Apodemus sp., and shrews Crocidura sp.) and insects (F%57.3%; V%54.0; mainly large-sized ground beetles), represented food sources of minor importance. On the whole, diet composition did not differ from that reported for northern Italy by various authors (Kruuk & de Kock 1981; Prigioni et al. 1988; Biancardi et al. 1995; Lucherini & Crema 1995; Balestrieri et al. 2004).
if reproduction occurs. The lack of information about badger breeding success in the first three years of the reintroduction project is probably the main limitation of our monitoring programme. The enclosure minimum size and the duration of captivity are fundamental parameters for acclimatisation: too long a time in inadequate conditions can cause stress, influencing survival rates (Sjo¨a˚nsen 1996). The enclosure size was sufficient to prevent social tensions among badgers and the fact that the individuals successfully foraged for earthworms within the enclosure suggests that their natural behaviour was not greatly compromised by captivity. Even though many other factors could have been involved, acclimatisation time seemed to represent an important factor to prevent homing behaviour: a minimum captivity time of 3–4 weeks being sufficient to minimise the probability of erratic movements. Furthermore, longer captivity times did not seem to have negative consequences upon postrelease behaviour.
Conclusions The number of released animals over the duration of a reintroduction programme can markedly affect its success (Griffith et al. 1989; Stanley Price & Fairclough 1997). Adverse environmental or climatic stochastic effects are more prevalent in small founder populations (Gilpin & Soule´ 1986); moreover, dispersion or erratic movements and reproductive failure can easily jeopardise population success (Durant & Mace 1994). Nevertheless, each reintroduction is a particular case (Wolf et al. 1998) and literature reports about translocations successfully carried out with relatively few founders released in a number of years (Copley 1994; Arquillie`re 1998; Breitenmoser et al. 1998; Aubry & Lewis 2003). Four family groups of a relatively long-lived species, such as the badger, released over a fouryear period, could represent a suitable founder stock,
Figure 1. Montevecchia and Curone Valley Regional Park (Lombardy, northern Italy); the polygon shows the current area of activity of the badgers, as outlined by radio-telemetry and field signs; the spot marks the acclimatisation enclosure.
Badger reintroduction Although Griffith et al. (1989) did not find any association between reintroduction success and the physical condition of released animals, it is unquestionable that infectious diseases can be wasting for a small population. Little is known about badger diseases in Italy: TBC or other epidemics have never been reported (O.I.E. 2003). Considering trap site distances, the chance of introducing dangerous diseases in the release area can be considered to be extremely low, as suggested by long-term survival of introduced badgers. Nevertheless, more careful medical screening would have permitted us to assess the cause of death of M2 and to steadily exclude the risk of epidemics. Human interference seemed to negatively affect the first steps of the reintroduction, even if all badgers came from setts usually exposed to disturbance, but, on the whole, the protected area confirmed the predictions of the feasibility study: home range size and diet composition of released animals are signs of a suitable habitat for badgers. The present distribution of the badgers in the park and the confirmed breeding activity of the last released group leads us to think that the presence of the mustelid could progressively become more stable at least in the lower Curone valley. Translocations aim to establish a self-sustaining population (IUCN 1995): the local public, who were made aware of the reintroduction project through hand-outs and other popular publications, now ask for final (and prompt) results, which are now fundamental to enhance the park’s role in nature conservation. More monitoring is needed to determine whether the badger population is at sustainable levels or if more translocations should be considered. Acknowledgements We wish to thank the Montevecchia and Curone Valley Regional Park, particularly Michele Cereda, for the financial and technical support to the project. Nadia Scaramoncin and Federica Rigamonti assisted with fieldwork for their degree thesis (University of Milan). We are grateful for comments and criticism from two anonymous referees, Chris Newman and Jim Conroy. References Arquillie`re A. 1998. Experimental reintroduction of brown bears in the French Pyre´ne´es. Oryx 32:8–10. Aubry KB, Lewis JC. 2003. Extirpation and reintroduction of fishers (Martes pennanti) in Oregon: Implications for their conservation in the Pacific states. Biological Conservation 114:79–90.
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