Management of rabbits (Oryctolagus cuniculus) on St Helena: a case
study.
St Helena
St Helena is an oceanic island 12,170 ha in size, located in the sub-tropical Atlantic ocean (Ashmole &
Ashmole 2000 in Bell & Boyle 2008). The island is a self-governing British Overseas Territory with a
governor appointed from Britain. St Helena is of high conservation value as it has a number of endemic
plants and birds. However the introduction of invasive species such as livestock, rabbits, rats and cats
have caused the extinction of at least six endemic plant species, and all but one of the endemic birds
(wirebird remains) (Bell & Boyle 2008). St Helena is one of the five territories part of the European Union's
South Atlantic Invasive Species Project (SAIS); a three year (2006-2009) project which aims at increasing
these territories’ ability to deal with invasive species.
Rabbits on Saint Helena
The rabbits present on St Helena are the smaller, darker Mediterranean subspecies Oryctolagus
cuniculus huxleyi. They were first introduced to St Helena by Portugese explorers in the early 1500 but
were exterminated by feral cats before the 16th century (Ashmole & Ashmole 2000 in Bell & Boyle 2008).
They were then reintroduced in 1770 and have subsequently spread across the entire island. Since 1838
rabbits have been listed as a game species and were hunted by locals (Bell & Boyle 2008).
Rabbit surveys on the island estimate the distribution to be between 3 and 4 rabbits per hectare based on
number of pellets deposited, and around 30,000 rabbits in total. Compared to countries like New Zealand
which has densities of up to 50 to 100 rabbits per hectare, the total numbers of Saint Helena are relatively
low (Miller 2008). Distribution is not even across the island and varies based on vegetation, climate and
land use. Densities are high in prickly pear groves which provide safety from predators and hunters, and
at areas that are highly productive or provide good burrowing habitat. The highest density recorded was
at Man and Horse, reaching an estimated 20 or 30 rabbits per hectare, where hunting is prohibited due to
a population of wirebirds (Bell & Boyle 2008).
Numbers of rabbits on St Helena are thought to be increasing in recent times due to “greening” of the
island (R. Cairns-Wick in Bell & Boyle 2008) and changes in farming practices and reduction in hunting by
the local community (Bell & Boyle 2008).
Perception of rabbits on St Helena
Surveys and meetings with interested parties, residents, government officials and agencies were
conducted to determine impacts and opinions on the rabbit situation on St Helena.
In general the public response was that the public liked the rabbits and did not want them completely
eradicated from the island. The public felt that the rabbits did not cause significant problems, and were
happy to deal with them themselves when they caused minor problems, such as being garden pests.
Many of the locals enjoyed seeing rabbits and the wild, and shooting them for food. In general the public
felt that trapping and shooting rabbits was acceptable, but poisoning or using a virus was not.
Local farmers tended to have more serious concerns about the rabbits; some reporting a total loss of
crops caused by rabbits at times. In general farmers were more open to a poisoning programme, stating
the issue of time needed to check traps. Repellants were also favoured as a control method.
Agencies such as the St Helena Growers Co-op and the Agricultural Department (ANRD) experienced
significant problems from rabbits eating stock plants, fruit, crops and flowers. While the Growers Co-op
were happy for a trapping operation, or to use repellants they were opposed to wide-scale poisoning; the
ANRD were not opposed to a poison bait programme and expressed interest into investigations of bait
type, bait quantity, bait station design etc.
The St Helena Environmental Health Department (SHEH) had received public complaints about rabbits,
and as such had been dealing with them. However they note that rabbits are of low priority compared to
rats and feral cats. They had investigated introducing a disease such as myxomatosis, but acknowledged
that it was unlikely to go ahead due to lack of public support, and instead felt that a public awareness
campaign about the options for rabbit control would be more effective.
The St Helena National Trust and the Millenium Forest Project were concerned about rabbits in planting
schemes, and that rabbit numbers help maintain high numbers of predators in endemic wirebird habitat.
Impacts of rabbits on St Helena
Rabbits are an important agricultural and horticultural pest on St Helena. The St Helena Growers Co-op
have had problems with rabbits eating stock plants and the Agricultural Department (ANRD) have noted
concerns with fruit, crops and flowers being damaged by rabbits. Discussions with local farmers revealed
that at times they experienced total loss of crops caused by rabbit browsing (Bell & Boyle 2008).
Horticultural production at Longwood and Sandy Bay can suffer up to 100% losses of young plants by
rabbits, having a direct impact on island agricultural production. Rabbits also graze on pasture land,
which although is not as noticeable, reduces food available for sheep and other livestock (Miller 2008).
Rabbits also threaten the islands's five endemic plant species through browsing, and are particularly
damaging to young native plants growing in drier coastal zones (Miller 2008).
Rabbits may also help maintain high predator numbers. In two of the best habitats for endemic wirebirds
on St Helena rabbit numbers are particularly high, possibly due to the hunting restriction. As a result feral
cats, which predate wirebirds, are also found in high numbers (Bell & Boyle 2008).
Control methods
Control should focus on areas that would have the most benefit to people or habitat (i.e. around farms,
settlements, wirebird habitat or replanting areas). Furthermore, because rabbit control is complicated by
interactions with other invasive species such as feral cats and rats, control must be developed as an
integrated programme for all three species to maintain the predator-prey balance, i.e. only controlling
rabbits would be likely to increase predation on wirebirds and other bird species. Rabbit populations can
withstand high morality, so control methods must limit the population to a level that impacts caused by
rabbits are reduced to an acceptable level (Bell & Boyle 2008). At present there is limited control being
done which includes use of repellents, trapping/shooting and hunting.
Bell and Boyle (2008) list the following as practical control methods for rabbits in St Helena:
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Warren destruction
Trapping
Fumigation
Shooting
Repellents
Rabbit-proof fencing
Disease (RCD)
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Poisoning
Warren Destruction
Destruction of rabbit warrens or “warren ripping” can be carried out by digging them out manually with
shovels or spades or using machinery such as bulldozers. Destroying burrows is effective as it prevents
rabbits from reinvading areas (Bloomfield 1999; Farrelly & Merks 2005 in Bell & Boyle 2008).
This method has limited use for St Helena as the island has limited warren systems; most rabbits live
above ground. Furthermore most of the areas with burrows are wirebird habitat, or have important plant
species growing. As this method targets only rabbits it may upset the predator-prey balance. However
warren destruction could have some limited short-term use in some locations (Deadwood Valley, Netley
Gut and Man and Horse) (Bell & Boyle 2008).
Trapping
The use of traps can be an effective means of controlling rabbits; particularly where the population is not
particularly high. Trapping is very practical for St Helena, particularly in small-scale operations around
nuisance areas. Trapping has a number of advantages including, good opportunities for public
involvement, release of non-target animals unharmed, and potential for long-term use. However trapping
is very labour intensive and the initial cost of purchasing traps is high. Ongoing labour costs would also
be incurred. The total cost could be up to £250 per ha, depending on trap type. Furthermore there is the
potential for trap shyness to develop which would limit effectiveness, and the issue arises again of just
targeting one species, rather than all three.
Cage traps are recommended over spring traps, snares and netting (due to ethical issues and non-target
capture) on St Helena. Drop boxes could also be used in conjunction with rabbit-proof fencing. Cage
traps are usually rectangular wire mesh (68 x 25 x 23cm) with a treadle which activates a wire mesh door
and are baited with carrot or similar. They range in price from £20 to £70, but the recommended design
known as Havahart Humane Rabbit trap is priced at about £35 and is readily available in the UK. The
cage trap design is generally viewed as one of the most human methods of rabbit control (DEFRA 2004
in Bell & Boyle 2008), as the animal is not killed. Traps must be checked twice daily. Non-target animals
are released while rabbits (or other target animal) is killed by a sharp blow to the head with a heavy stick,
or by shooting (DEFRA 2004 in Bell & Boyle 2008).
Fumigation
Fumigation, the depositing of a chemical inside the entrances of rabbit warrens or burrows, has been
shown to be extremely effective at controlling rabbits where burrows are accessible (Pepper 1998;
Bloomfield 1999; DEFRA 2004 in Bell & Boyle 2008).In St Helena this method is only practical in a few
areas (such as Netley Gut) where rabbits use burrows and warren systems.
Additionally fumigation is expensive (up to £500 per ha), requires qualified and licensed personnel, can
be dangerous to public.
Shooting
Shooting is reasonably effective at controlling rabbit populations; it is usually used where populations are
not excessively high. Shooting is often conducted at night using a spotlight (Bloomfield 1999 in Bell &
Boyle 2008). However shooting operations are thought to only reduce rabbits by approximately 30%, and
tend to target males. Rabbits may also become wary of shooting campaigns; reacting to spotlights or
gunshots. Shooting is highly labour intensive and time consuming, but has the advantage that it involves
the public and rabbits can be eaten. Indeed locals on St Helena have indicated that they would like to
hunt more often. The main cost of shooting to control rabbits is labour costs, estimated to be up to £150250 per ha, unless local community are involved voluntarily. Shooting is best combined with other
techniques and used in areas where populations are not overly high.
Repellents
Repellents are sprayed onto plant surfaces to deter rabbit feeding. However the use of repellents is
expensive (£300-500 per ha) and only provides short term control against rabbits. Repeated applications
are required, and thus they are usually restricted to individual trees, small plantations or areas that cannot
be protected by any other means (Pepper 1998; Bloomfield 1999; DEFRA 2004 in Bell & Boyle 2008). AA
ProtectTM has been used successfully in St Helena and the UK; however recent research indicates that
some chemicals in the repellent may affect germination rates of some tree species (Gosling& Baker 2004
in Bell & Boyle 2008).
SAIS (n.d.,b) also report of a “homemade” recipe for a rabbit repellent which is non-toxic and persists in
the field for longer. This recipe was developed by the Depratment of Conservation (DOC) in New Zealand
and consists of dried egg powder mixed with an acrylic resin emulsion and water. The mixture can be
then be sprayed. See SAIS (n.d.,b) more details and the recipe.
Rabbit-proof fencing
Fencing is particularly useful in areas where other control methods are impractical such as small farms or
important areas (such as conservation or plantation areas). Fences are particularly effective in
conjunction with other control methods such as drop box traps. Drop box traps consist of a tunnel which is
inserted into the wire fence line. Rabbits are caught when they enter the tunnel and fall through a hinged
flap into a box that is buried in the ground. Like all traps they must be checked regularly and animals
killed humanely.
Well constructed and maintained fences are long-term solutions. The initial cost is high (£50-100 per m,
excluding labour costs), but this cost is essentially one-off, apart from maintenance and inspection costs.
On St Helena fencing costs are estimated to be £150 per metre, not including site preparation, travel,
labour, accommodation and food costs.
Individual trees may also be protected using tree guards, for young and/or important trees, where it is
impractical to fence them into a larger area. Tree guards should be at least 1m in height and give the
plant room to grow and spread. Tree guards have been used with moderate success on St Helena. They
cost around £1 each.
Rabbit calicivirus disease (RCD)
Rabbit calicivirus disease (RCD), also known as rabbit haemorrhagic disease (RHD) or viral
haemorrhagic disease (VHD) is a viral disease that is specific to rabbits. RCD works by overloading the
immune system, and rabbits may die after just 30 hours (Bloomfield 1999 in Bell & Boyle 2008). However
rabbits under ten weeks old may gain immunity.
RCD is rabbit-specific and an environmentally “clean” option for control. Infected rabbits may still be eaten
as the virus poses no threat to humans. RCD is thought to be a very practical, cheap and long-term
means of controlling rabbits on St Helena. However RCD effectiveness depends on a number of factors
including climate, vector numbers, density of adult and juvenile rabbits and warren site and size; many of
which are unknown on St Helena. The virus has low efficiency at low rabbit densities. Thus there is a
significant amount of research required before RCD can be considered for release in St Helena.
Furthermore, public support for RCD is low.
Poisoning & baiting
Baiting is one of the most efficient and cost effective methods of controlling rabbits on a large scale
(Devine & Cook 1998; Bloomfield 1999; Farrelly & Merks 2005 in Bell & Boyle 2008). They have been
successfully used to eradicate rabbits from a number of islands around the world, and to control
populations on mainland (Bell 2001; Bloomfield 1999; Torr 2002; Courchamp et al. 2003 in Bell & Boyle
2008). Cereal-based pellet baits containing toxins are used in most cases. Brodifacoum, pindone, sodium
monofluroacetate (1080) are some commonly used toxins, although pindone is usually used for rabbit
control. Baits are dyed green-blue to avoid take by birds. Rabbits will take bait from plastic bait stations;
however ground or aerial operations are more successful (Brown 2001 in Bell & Boyle 2008). Non-target
and secondary poisons are more common in these cases (Brown 2001 in Bell & Boyle 2008).
Pindone (2-pivaloyl-1,3-indandione) is a first generation anticoagulant, which although first developed for
rodents, proved more effective on rabbits in New Zealand and Australia. Pindone works by interfering with
the vitamin K dependent clotting factors in the liver, but is much less persistent that second generation
anticoagulants such as brodifacoum. Pindone is slowly degraded in soil, and has a persistence in tissue
of 8-10 days, with no residues remaining after 14 days (Eason & Wickstrom 2001 in Bell & Boyle 2008).
Birds are suseceptible to pindone, and a number of mortalities of passerine and raptor species have been
recorded after aerial applications of the poison in New Zealand (Eason & Wickstrom 2001 in Bell & Boyle
2008).
Because it is a first generation poison, pindone requires a very large single dose or repeated smaller
doses to cause death. A single dose of 18mg/kg is sufficient to kill rabbits (Eason & Wickstrom 2001 in
Bell & Boyle 2008). The poison can be put in bait stations, but is more effective if pellets are openly laid
on the ground; although some bait station designs are more effective than others. In open lay
programmes pellets should be thinly scattered across the ground (about 4kg/ha), rather than placed in
piles. Bait should be provided in areas where the rabbits feed, rather than near burrows. Freshly dug
ground, which rabbits are attracted to, should have bait distributed (Bell & Boyle 2008). It is important that
trials are undertaken on St Helena to determine the best poison programme design.
Considerations
There are a number of legal issues to be taken into consideration. Poison baiting and use of rabbitspecific diseases cannot be used in the UK. However it is not known if these restrictions apply to St
Helena. A number of legal acts relate to control of rabbits in the UK (See Bell & Boyle 2008 for more
detailed list). The Protection of Animals Act 1911 prohibits the laying of poison baits for rabbits and also
requires that spring traps are inspected at least once per day. The Prevention of Damage by Rabbits Act
1939 regulates the use of poisons to control rabbits, but is restricted to fumigants in rabbit holes or
repellents. The Wildlife and Countryside Act 1981 prohibits self-locking snares. Other snares must be
checked twice daily and cannot be used where they pose a risk to other animals. The Wild Animals
(Protection) Act 1996 makes it an offence to inflict unnecessary suffering on any wild animal. The
Specified Animal Pathogens Order 1998 prohibits the introduction of RCD, except under a special licence
(usually refers to laboratory experiments). The Pests Act 1954 states that landowners may use any legal
method to control rabbits on their land, and specifies the types of traps and checking restrictions that
apply.
In addition there are several St Helena Ordinances that may have relevance to rabbit control. The St
Helena Wildlife Protection Ordinance states that those wanting to kill animals must obtain a licence from
the government. However the animals listed do not include rabbits, which follows that a licence is not
required to kill rabbits. The St Helena Protection of Animals Ordinance states that anyone laying poisons
for rats, mice and other small vermin must take reasonable precautions to prevent access to dogs, cats
and other domestic animals. It is likely that this ordinance will relate to poisons set for rabbits also. The
Animals (Diseases) Ordinance 2001 prevents the introduction of disease or diseased animal to St
Helena, which has relevance if rabbit diseases are to be used as rabbit control.
Recommendations and improvements for control
Any improvements to control of rabbits on St Helena will require an increase in staff numbers and
funding. As previously mentioned, the public opinion seems to be that trapping and shooting is preferred
over poisoning or rabbit-specific diseases. It is thus recommended that more traps are purchased and
supplied to local residents, the Grower’s Association and farmers for regular rabbit control. An intensive
wider-scale trapping campaign of rabbits (and feral cats – to maintain predator prey balance) in the most
affected areas (Sandy Bay and Longwood Farm) would reduce impacts on crops and gardens.
Additionally the employment of a local trapping officer is recommended, if enough funding can be raised
(Bell & Boyle 2008).
Hunting restrictions and legal issues on St Helena need to be clarified. It may be necessary to open some
restricted areas, e.g. wirebird habitat, where rabbits cause significant damage. Opening of these areas
would need to be timed to reduce the risk to non-target species. Awareness of hunting could be increased
through local hunting competitions, which would increase enthusiasm about hunting and involve local
community (Bell & Boyle 2008).
Rabbit-proof fencing is recommended at some of the worst affected areas including farms, properties and
conservation areas. As with all control measures; obtaining funding is a major restriction. Purchase and
freight costs of materials needed for fencing restrict most farmers from fencing their properties. If fence
materials were provided to farmers, many of them have indicated that they would be interested in fencing
valuable areas (Bell & Boyle 2008).
Research into life history, breeding cycle, frequency of breeding and behavior of rabbits on St Helena is
strongly recommended. This information will enable long-term solutions to such as poisoning or
introduction of RCD to be investigated. Trials using non-toxic baits to determine whether rabbits will take
pellets and what formulation they prefer and what bait station design is the most effective should also be
undertaken. This information would be valuable for planning of island-wide control or eradication in the
future. Additionally the legal aspects of these control methods will need to be investigated. An education
and advocacy programme may also be required with these control methods, as the public opinion
towards poisoning and rabbit-specific disease is in general, negative (Bell & Boyle 2008).
Conclusions
St Helena is an island of high conservation value due to its unique plants, birds, animals, history,
archaeology, and scenery. Thus it is crucial that the special features of the island are maintained during
any control programme. No aspect of the island is more important than another, and priorities must be
determined and in some cases difficult decisions may be made. The recovery of St Helena will be a long
and difficult process. Detailed management strategies are important for the direction and status of the
island, to ensure that the uniqueness of St Helena is maintained for the flora and fauna, public and
scientific community (Bell & Boyle 2008).
References
Bell, E. & Boyle, D. (2008). Rabbits on St Helena: assessment and advice on the rabbit situation in St
Helena. EU South Atlantic Invasive Species Project.
Miller, C. (2008).Increasing regional capacity to reduce the impacts of invasive species on the South
Atlantic United Kingdom Overseas Territories, Volume 2. Interim Report 2, European Commission.
South Atlantic Invasive Species Project (SAIS). (n.d.,b). Invasive species information sheet: rabbit
repellent.