Course:CONS200/2023WT1/Feral Rabbits in North America and Their Impact on Wild Ecosystems

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Brief Introduction

Abundant in population and under the guise of a harmless creature, invasive rabbit species pose considerable threats to native ecosystems. As European culture first used rabbits as a source of food, their domestication spread and was eventually introduced to North America.[1]

History & Context

When the European rabbit was first discovered, it was found residing in the Iberian Peninsula. Early settlers quickly discovered their extremely quick breeding capacity under “captive conditions” that led to it being sought after in terms of exploitation as a food source.[2]

Oryctolagus cuniculus, rabbit.

It is worth noting the distinction between the European rabbit and the native American cottontail rabbit. Firstly, European rabbits are far more sociable, creating and establishing family residences by burrowing underground. Due to a relatively consistent routine of living conditions, they are far easier to locate and capture for captivity, easier also to mimic ideal living conditions by domesticators in order to readily reproduce their numbers.[3] The American cottontail is also far more rich in species diversity, therefore, when that attribute is combined with its lower sociability, it is evident why they have not become domesticated.[3]

Due to European rabbits' reproductive rates and resilience to adverse conditions that would normally lower the numbers of other species, they are able to live in a plethora of conditions and climates. Once introduced to foreign land, they inevitably manage to avoid natural predators, eventually resulting in an invasive abundance of numbers, seeing reproductive success in most continents across the globe.[2]

Since they are invasive species everywhere except their native land, the European rabbit deeply negatively impacts the ecosystems they inhabit, completely altering their foundational ecology. To be more specific, they consume native vegetation far too quickly, degrading soil quality and habitat.[2]

Background

With the history and context discussed, this wiki page can now move onto the background of the current issues revolving around the invasive feral rabbit issue in North America. There is a distinction to be made between the American cottontail species and the European domesticated rabbits. The term feral rabbits are those that have been domesticated and released into the wild, or descendant from previously domesticated rabbits.[4] In North America, the most common feral rabbit is the European rabbit, which was introduced to North America roughly 100 years ago and is now listed on the top 100 worldwide invasive species list.[1] Currently, their presence is detrimental to local ecosystems. In fact, they “compete with many native species for food and shelter. And their “intense grazing and burrowing behaviours also cause considerable soil erosion”.[1]

It is also important to note the alarming rate which feral rabbits can reproduce. Those that are released into the wild can bear 18-30 young per year amid an abundance in resource availability. As a primary consumer and herbivore, feral rabbits consume incredibly large amounts of vegetation over their lifespan, destroying the plant sources that all life depends on in the ecosystem.[1] However, their abundance is good for secondary consumers, as feral rabbits are now the second “most important food for bald eagles” in areas such as the San Juan islands.[5] Other species that are now dependent on them include golden eagles, red-tailed hawks, and great horned owls.[5] This will inevitably cause the downfall of the native food chain as feral rabbit populations reach their carrying capacity due to overpopulation and the loss of vital food sources - eventually declining the stability of the above-mentioned predators.

Spread of Disease

Feral rabbits may impact their surrounding ecosystems by the spread of disease. The main disease that has been studied and documented is Rabbit Hemorrhagic Disease (RHD) which is spread via Rabbit Hemorrhagic Disease Virus (RHDV) and subsequent strains of the virus such as RHDV2. RHDV is extremely contagious and has a high mortality rate, killing rabbits within 12-72 hours of the onset of fever.[6] It primarily affects the tissues of the lungs, liver, and spleen, and presents a variety of visible symptoms depending on the type of infection.[6] In peracute infections, rabbits show no visible symptoms and die suddenly.[6] In acute infections, visible symptoms are severe and include anorexia, opisthotonos, paralysis, ataxia, foamy and bloody nasal discharge, and ocular hemorrhages.[6] In subacute infections, symptoms are similar, albeit more mild, and rabbits typically survive and therefore develop antibodies against RHDV.[6] The most common cause of death from RHDV is disseminated intravascular coagulation which leads to abnormal blood clotting, resulting in hemorrhages and congestions in many organs.[6] RHDV2 is becoming more common in recent years, and while it has similar traits to RHDV,  it can infect a broader range of hosts, is more likely to infect young animals than RHDV, and can infect and kill rabbits that already have antibodies to RHDV.[7]

There are multiple ways that RHDV is spread. It can be spread directly via contact with secretions and excretions from infected animals, or indirectly through contaminated food, water, or via vectors like insects.[6] In the wild, carcasses of infected rabbits may be a major viral source because the virus remains relatively stable throughout exposure to harsh environmental conditions.

Given the high transmissibility of RHDV, it has spread across the globe, with the first documented case in North America occurring in the early 2000s.[6] More recently in 2020 there was a major outbreak of RHDV2 in native rabbits like jackrabbits (Lepus spp.) and cottontails (Sylvilagus spp.) in the southwestern United States and Mexico, following a documented case in a domestic rabbit in New York, USA.[7] It was not confirmed if the domestic rabbit passed RHDV2 onto wild lagomorph populations. However, it has been suspected in other cases that the release of infected domestic rabbits is the viral source for feral populations, which are more likely to pass it on to wild populations.[8] RHDV2 has now been confirmed in over 10 US states all over the country, indicating that it will likely continue to spread and infect more feral and wild lagomorphs. RHDV2 was also documented in British Columbia throughout 2018-2019 when an outbreak occurred in feral and domestic rabbits on Vancouver Island and the adjacent coast of the mainland of British Columbia.[8] In this case, there was no documentation of the virus spreading to wild rabbit populations, and it remains unclear if this particular strain of RHDV2 is pathogenic for wild lagomorphs in this area.

Environmental Impact

Feral rabbits can impact the environment through activities related to their feeding and housing. Overgrazing is often their biggest impact on ecosystems.[5] Rabbits are generalized herbivores, which means they will eat most plants from grasses to young trees. They will usually eat all parts of a plant, and will even dig under the plant to eat roots as well as eat the seeds before the plant disperses them.[1] This means the rabbits are able to prevent plants from reseeding and could cause local extinctions to more sensitive native plant species.[9] Their grazing can shift landscapes from originally having mostly perennial grasses to having mostly annual grasses, which decreases the stability of the ground and therefore increases the risk of soil erosion.[10] Removing vegetation cover from an area will also have negative impacts on soil stability due to the decrease in plant roots holding the soil together as well as the lack of shade provided by vegetation causing more evaporation and therefore drier, less stable soil. Feral rabbits can live in any ecosystem that allows them to burrow, which means they can be found anywhere from deserts to coastal plains.[9]

Rabbits will burrow and make tunnels underground for safe shelter from predators. Extensive rabbit tunnel networks can drastically change the landscape through changing water flow patterns, for example allowing water to pool underground in the tunnel networks during heavy rain periods (Pickard, 1999), and decreasing surface water runoff ability through the mounding of soil around burrow entrances.[10][11] These changes along with soil compaction impacts will also increase soil erosion risk, with more extensive burrowing networks increasing the risk of sinkholes and other soil collapse events.[1]

Feral rabbits can also have an impact on human-populated and urban areas. They can  decrease agricultural yield either through directly eating crops or indirectly changing crop fields with burrowing activities, and can also cause major property damage with these activities.[12] Human land-use changes don’t have a strong impact on feral rabbit activities, which means feral rabbits are common in areas used by people.[10] One well-known example is the feral rabbit problem that the University of Victoria experienced up until they successfully sterilized and relocated this population of over one thousand rabbits in 2011.

Feral European rabbits are on the top 100 invasive species list worldwide.[1] They can adapt to many environments & situations due to being generalized herbivores, and also breed more prolifically than native rabbit species.[12] Therefore, they can easily outcompete native species for food and shelter. European rabbits originated in Iberia, where they are actually a threatened native species. In Iberia, European rabbits are subject to conservation efforts due to their crucial role in the Iberian ecosystems as food for over 40 vertebrate predators.[5] European rabbits can cause drastic changes in ecosystems where they are an introduced species, but over time the ecosystem starts to rely on them as a food source and it would do more harm than good to remove established feral rabbit populations in some ecosystems.[5]

Feral Rabbit Management

With the spread of diseases, and landscape destruction associated with the growing populations of feral rabbits, mitigative strategies need to be creative to decrease their occurrence in the wild.[13] Once in the wild, feral rabbits are difficult to control due to their high reproductive rates, and wide-spread dispersal, however, strategies such as fencing, and trapping could lead to improved control of their impacts.[14] With landscape degradation being a primary concern associated with feral rabbits, the combined approach of trapping and fencing would allow for areas of land to be protected from overgrazing and habitat alterations.[13] In targeted areas such as Jericho Beach, an adaptive management technique could be created in which feral rabbits are trapped and relocated to a fenced area.[13] Permits and bylaws have been dropped regarding the trafficking and relocation of feral rabbits, allowing this mitigation strategy to be implemented easier.[15] By creating a barrier between protected land and invasive species, ensures that the rabbits can continue to live in a wild domain while still maintaining the integrity of much of the area. While this may be costly to implement, it ensures the long-term protection of landscapes, with minimal to no harm on feral rabbits.[13]

Efforts to control the current population of feral rabbits will only be effective if the prevention of further introduction of pet rabbits to the wild is in place.[13] While bylaws in Richmond have been made, preventing the feeding, and dumping of feral rabbits on public grounds, lack of enforcement, and regulation have led to the continued occurrence of owners releasing their pet rabbits to the wild.[16] City governments are hesitant to create new bylaws, as many are already in place such as the banning of rabbits being sold at pet stores, and a limit of two rabbits per household, however, the lack of execution on administering these bylaws has led to them generating minimal improvement on the issue.[16] The enforcement of these bylaws could be more publicly known through government commercials, park signs, and news reports, and if penalties were heightened such as increased fines, BC residents would be more aware and conscious of the severity of the situation.[15]

Natural fencing that could be used as a mangement strategy.

While rabbits are banned from being sold in pet stores, owners are still able to adopt them as companions from shelters. Although this is beneficial to create space for the influx of rabbits in BC animal shelters, proper steps and processes should be made to ensure that new owners meet the qualifications required for long-term rabbit care.[17] By interviewing potential rabbit owners with a series of questions regarding their knowledge on rabbits and what their care entails, it can assess if owners are well-suited to adopt these animals. Similarly, contracts can be created and signed in which new owners agree to the long-term care of rabbits, ensuring that they understand that their adoption of these animals is not temporary, and they agree to all responsibilities their new pet will bring.[18] While verbal and written agreements can decrease the likelihood of impulsive pet purchases, the chance that an adopted rabbit is released to the wild is still possible. In the instance that this occurs, it could lead to further growth of feral rabbit populations, so a prospective solution could be the sterilization of adopted rabbits. Similar to the measures taken for cats and dogs, minimally invasive sterility treatments could be given to female rabbits in animal shelters.[19] The sterilization of adopted rabbits ensures that in the unfortunate case that they are released to the wild, they will not be able to reproduce, preventing the increase in feral rabbit populations.[19]

Future Research Suggestions & Implications

More research focused on the spread of RHDV and RHDV2 from domestic, to feral, to wild rabbit populations in North America is needed. While there is documentation of this virus occurring in these populations, there is limited information on its transmission between them.[7][8] Further research into the spread of RHDV and RHDV2 between these populations is important as it will provide better understanding of the impact feral rabbits have on wild rabbit populations and how to control the spread of this virus. The transmission of other highly infectious diseases such as avian influenza A viruses via feral rabbits represents another knowledge gap. There is evidence that wild cottontail rabbits can shed this virus, which suggests that it could also be spread via feral rabbits and therefore should be studied to understand the risk of transmission from feral rabbits to other organisms.[20]

The impact of feral rabbits on native vegetation as well as vertebrate and invertebrate populations in North America represents another knowledge gap. This has been researched in other regions, such as Macquarie Island where there have been massive declines in tall tussock and megaherb vegetation due to a large increase in feral rabbit numbers.[21] It is possible that feral rabbits will have or are already having similar negative impacts on native vegetation in North America, but further research is needed to determine this. Additionally, research should be conducted on the impact feral rabbits may have on the habitat of other vertebrate and invertebrate species in North America through their destruction of vegetation and degradation of soil.[2]

Finally, research should be conducted on biocontrol of feral rabbits in North America as a potential future mitigation strategy. RHDV and myxoma virus have been used as a biocontrol in Australia with variable success.[22] A sterilizing strain of myxoma virus has also demonstrated potential to reduce long term rabbit populations.[23] Research on the application of these biocontrol methods in North America is advised to determine their effectiveness for controlling feral rabbits in this region, and whether release of these viruses would have negative impacts on non-target organisms.

Conclusion

The European rabbit has become an invasive species worldwide due to its ability to adapt to different climates along with its high reproductive capacity. Feral rabbits can wreak havoc on natural ecosystems, causing erosion, water flow pattern changes, vegetation loss, soil degradation, changes in the food web, and a decline in native species abundance and diversity. One of the main concerns regarding feral rabbits is their ability to spread disease to native and pet rabbit populations. Major diseases of concern include Rabbit Hemorrhagic Disease (RHD), which spreads easily and has a very high mortality rate. Feral rabbits can also cause problems for agriculture, reducing crop yields and destroying fields through burrowing. They can live in urban areas easily and can destroy property.

Mitigative strategies include the strategic building of fencing, trapping, and capture-sterilize-release programs, along with bylaw enforcement involving the acquisition of rabbits as pets. Future research should include the factors influencing the spread of rabbit diseases such as RHD, along with mitigative biocontrol strategies for disease spread prevention. The impacts that feral rabbits are having on North American vegetation and ecosystem composition should also be looked into, along with their impacts on native species in North America, specifically the wild rabbit species with which they compete and the predator species relying on feral rabbits as a food source. Overall, the feral rabbit populations in North America have caused major changes to the area and will continue to impact many different facets of human and animal life.

References

Note: Before writing your wiki article on the UBC Wiki, it may be helpful to review the tips in Wikipedia: Writing better articles.[24]

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Government of British Columbia (n.d.). "European Rabbit Invasive Species Alert" (PDF). Government of British Columbia.
  2. ↑ 2.0 2.1 2.2 2.3 Naff, K. A. & Craig, S. (2012). Chapter 6 - The domestic rabbit, Oryctolagus cuniculus: Origins and history. M. A. Suckow, K. A. Stevens, & R. P. Wilson (Eds), American College of Laboratory Animal Medicine: The Laboratory Rabbit, Guinea Pig, Hamster, and Other Rodents (pp. 157-163). Academic Press. https://doi.org/10.1016/B978-0-12-380920-9.00006-7.
  3. ↑ 3.0 3.1 Ober, Holly (2021). "Why weren't New World rabbits domesticated? Archaeologists find the answer in rabbit social behavior". UC Riverside. line feed character in |title= at position 44 (help)
  4. ↑ "Position Statement on Feral Rabbits". BC SPCA. 2017.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 Lees, A.C.; Bell, D. J. (2008). "A conservation paradox for the 21st century: The European wild rabbit Oryctolagus cuniculus, an invasive alien and an endangered native species". Mammal Review. 38(4): 304–320.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 Abrantes, J., van der Loo, W., Le Pendu, J., & Esteves, P. J. (2012). Rabbit haemorrhagic disease (RHD) and rabbit haemorrhagic disease virus (RHDV): a review. Veterinary Research, 43(12). https://doi.org/10.1186/1297-9716-43-12
  7. ↑ 7.0 7.1 7.2 Root, J., & Gidlewski, T. (2023). Wildlife Disease and Health in Conservation (pp. 260–270). JHU Press. https://books.google.ca/books?id=A9HPEAAAQBAJ&dq=feral+rabbits+north+america&lr=&source=gbs_navlinks_s (Original work published 2023)
  8. ↑ 8.0 8.1 8.2 Himsworth, C. G., Leung, D., Byers, K., Joseph, T., Gordon, E., Schwantje, H., Pritchard, J., & Ambagala, A. (2021). An outbreak of rabbit hemorrhagic disease disease in British Columbia, Canada. Journal of Wildlife Diseases, 57(4), 983-986. https://doi.org/10.7589/JWD-D-21-00061
  9. ↑ 9.0 9.1 Government of Australia (2011). "Feral European Rabbit Oryctolagus Cuninculus -DCCEEW" (PDF). Department of Sustainability, Environment, Water, Population and Communities.
  10. ↑ 10.0 10.1 10.2 Butler, D.R. (2006). "Human-induced changes in animal populations and distributions, and the subsequent effects on fluvial systems". Geomorphology. 79(3-4): 448–459.
  11. ↑ Pickard, J. (1999). "Tunnel erosion initiated by feral rabbits in gypsum, semi-arid New South Wales, Australia". Zeitschrift Für Geomorphologie. 43(2): 155–166.
  12. ↑ 12.0 12.1 McDonald, F (2022). "Everything you never knew you needed to know about rabbits. Invasive Species Council of British Columbia".
  13. ↑ 13.0 13.1 13.2 13.3 13.4 Brown, A (2012). "Glovebox Guide for Managing Rabbits". Petsmart.
  14. ↑ Department of Jobs, Precincts and Regions (2023). "European Rabbit". Agriculture Victoria.
  15. ↑ 15.0 15.1 Clarkson, B. (2023). "Rabbit Rescue Society warns Vancouver's feral population is about to boom, unless the city steps in". CTV News Vancouver.
  16. ↑ 16.0 16.1 Hui, V. (2023). "Animal Rescue Group slams Richmond feral rabbit management plan". Richmond News.
  17. ↑ Welch, T. (2015). "Motivations for and thoughts toward rabbit ownership and factors contributing to companion-rabbit owners' knowledge". University of Guelph.
  18. ↑ Team, H (2023). "Resources for rescuers and shelters". House Rabbit Society.
  19. ↑ 19.0 19.1 Twigg, L.E.; Williams, C. (2002). "Fertility control of overabundant species; Can it work for feral rabbits?". Ecology Letters – via Wiley Online Library.
  20. ↑ Root, J., Bosco-Lauth, A. M., Marlenee, N. L., & Bowen, R. A. (2018). Cottontail rabbits shed clade 2.3.4.4 H5 highly pathogenic avian influenza A viruses. Archives of Virology, 163, 2823-2827. https://doi.org/10.1007/s00705-018-3907-6
  21. ↑ Scott, J.J., Kirkpatrick, J.B. Rabbits, landslips and vegetation change on the coastal slopes of subantarctic Macquarie Island, 1980–2007: implications for management. (2008). Polar Biology, 31, 409–419. https://doi.org/10.1007/s00300-007-0367-y
  22. ↑ Barnett, L. K., Prowse, T. A. A., Peacock, D. E., Mutze, G. J., Sinclair, R. G., Kovaliski, J., Cooke, B. D., & Bradshaw, C. J. A. (2018). Previous exposure to myxoma virus reduces survival of European rabbits during outbreaks of rabbit haemorrhagic disease. Journal of Applied Ecology, 55(6), 2954-2962. https://doi.org/10.1111/1365-2664.13187
  23. ↑ McLeod, S. R., & Twigg, L. E. (2006). Predicting the efficacy of virally-vectored immunocontraception for managing rabbits. New Zealand Journal of Ecology, 30(1), 103–120. http://www.jstor.org/stable/24056168
  24. ↑ En.wikipedia.org. (2018). Writing better articles. [online] Available at: https://en.wikipedia.org/wiki/Wikipedia:Writing_better_articles [Accessed 18 Jan. 2018].


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