European wild rabbits are a risk to 322 threatened native species in Australia – double the number at risk from cats and foxes combined (Kearney et. al., 2019). ‘Competition and land degradation by feral rabbits’ is listed as a key threatening process under the Commonwealth Environment Protection and Biodiversity Conservation Act (EPBC Act), and a Threat abatement plan has been prepared for rabbits. The threatened species at risk due, at least in part, to rabbits include plants, mammals, birds, reptiles, invertebrates, and even fish and amphibians.
Invasive rabbits compete for feed and shelter with native animals, but much of the environmental harm they cause comes from how they graze (which changes the structure and composition of vegetation communities), and because they help maintain feral predators.
Even at very low densities – 1 rabbit per 2 hectares (0.5 rabbits : 1 hectare), or 1 warren per 10 hectares – rabbits can prevent the recruitment of entire species of plants, due to their selective grazing and searching out of palatable seedlings. In this way, they affect the structure and composition of vegetation communities, including several endangered ecological communities. If rabbits are seen, they are probably already affecting native vegetation and the ecology of native animals.
Rabbits seeking shade near water during drought in 1991. No ground cover of any sort remains and the ground is littered with dung and rabbit prints. (Image: Schulz, G. NSW Govt)
Grazing by wild rabbits, reducing the survival and recruitment of plants, is one reason why they are a risk to many threatened plants. For more information see the links below.
Some plants, especially when they are seedlings, are like chocolate to rabbits. Akin to children on an easter egg hunt, they sniff them out and consume every one of them. Researchers demonstrated this by sparsely scattering lucerne pellets over a large area of semi-arid shrubland and recording how they were all found and consumed by rabbits.
To exacerbate this, many Australian plants germinate infrequently, often in response to episodic events like fire, infrequent wet summers, or flooding – and that may only occur once in a decade or two. For such plants, the mere presence of rabbits during a germination event can mean the loss of an entire generation of recruits. It can be a similar story for efforts in revegetation and the establishment of perennial horticultural or forestry seedlings.
Unfortunately, the events to trigger some episodic germinations can lead to rabbit resurgence, just when they are least wanted. Rabbits can escape bushfires in their burrows, emerging to be one of the first herbivores to greet new seedlings, influencing which plant species recover and which don’t. Heavy rainfalls that trigger many semi-arid and arid area plants to set seed or germinate, will also trigger breeding in rabbits – increasing the grazing pressure faced by seedlings.
References:
Lange RT & Graham CR. (1983) ‘Rabbits and the failure of regeneration in Australian arid zone Acacia.’ Aust. J. Ecol. 8:377-381.
Rabbit densities are a guide to their ecological impact; 1 warren per 10 hectares equates to 1 rabbit per 2 hectares (0.5 rabbits : 1 hectare), and is a threshold density. Above that, rabbits will most likely be exerting selective grazing pressure on vegetation and changing the structure of vegetation communities.
The density ratios are drawn from field studies and are supported by logic. Rabbit home ranges cover about 10 ha, so if warren density is high, there is overlap of home ranges between rabbits from different warrens (and every square metre of their home range is explored by rabbits). It is not until warren density is reduced below 1 warren to 10 ha that there are ‘gaps’ between rabbit territories and spaces where rarer plants can regenerate without being grazed.
A quick means of assessing abundance is to score the amount of rabbit dung (pellets) encountered in a 15 minute walk.
Rabbit density – rapid assessment guide. (Source: from Cooke, McPhee & Hart ‘Rabbits. A threat to conservation & natural resource management.’)
References
Bird P, Mutze G, Peacock D & Jennings S (2012) ‘Damage caused by low-density exotic herbivore populations: the impact of introduced European rabbits on marsupial herbivores and Allocasuarina and Bursaria seedling survival in Australian coastal shrubland.’ Biological Invasions 14, 743-755
Cooke BD. (1988) ‘The effects of rabbit grazing on regeneration of sheoaks, Allocasuarina verticillata, and saltwater ti-trees, Melaleuca halmaturorum, in the Coorong National Park, South Australia’. Aust. J. Ecol. 13:11-20.
Cooke B, McPhee S & Hart Q. ‘Rabbits: A threat to conservation & natural resource management. How to rapidly assess a rabbit problem and take action’. Bureau of Rural Sciences, with AWI & MLA
Forsyth DM, Scroggie MP, Arthur AD, Lindeman M, Ramsey DSL, McPhee SR, Bloomfield T, and Stuart IG. (2015) ‘Density-dependent effects of a widespread invasive herbivore on tree survival and biomass during reforestation’. Ecosphere 6(4):71. http://dx.doi.org/10.1890/ES14-00453.1
Lange, R.T. and Graham, C.R. (1983). Rabbits and the failure of regeneration in Australian arid zone Acacia. Australian Journal of Botany, 8(4), 377-381.
Mutze Cooke Jennings to come Mutze, J., Cooke, B. and Jennings, S. (2016a). Density-dependent grazing impacts of introduced European rabbits and sympatric kangaroos on Australian native pastures. Biological Invasions, 18, 2365–2376.
Mutze, G., Cooke, B. and Jennings, S. (2016b). Estimating density-dependent impacts of European rabbits on Australian tree and shrub populations. Australian Journal of Botany, 64, 142 – 152.
Plants whose survival in NSW is threatened by rabbits include Acacia carneorum, Grevillea kennedyana, Cynanchum elegans, Thesium australe and Lepidium hyssopifolium.
It has also been concluded that a number of long-lived tree and shrub species have their recruitment prevented or severely limited by rabbit grazing in arid and semi-arid Australia. They and their plant communities were at risk of being rated as ‘threatened’ species or communities.
Examples include Acacia spp; Hakea spp., Callitris gracilis, and communities of belah/rosewood (Casuarina pauper/Alectryon olefolius) and western Myall (Acacia pendula). Mulga (Acacia aneura), sheoak (Allocasuarina spp.) and buloke (Allocasuarina luehmannii) are likely to become extinct throughout their range if rabbits continue to prevent regeneration of seedlings (NSW Scientific Committee).
References:
Kearney SG, Carwadine J, Reside AE, Fisher DO, Maron M, Doherty TS, Legge S, Silcock J, Woinarski JCZ, Garnett ST, Wintle BA & Watson JEM. (2019) ‘The threats to Australia’s imperilled species and implications for a national conservation response.’ Pacific Conservation Biology. 25, 328. https://doi.org/10.1071/PC18024_CO
NSW Scientific Committee (2002) NSW Threatened Species Conservation Act ‘Competition and grazing by the feral European rabbit – Final Determination’.
Although the impact from rabbit grazing is often severe, even at low densities, it is often unseen. Rabbits don’t remove giant, ancient trees from the landscape. Instead, they remove trees while they are tiny seedlings – before they are noticed. The consequence is even worse because they rob the locale of all the benefits those plants would have provided if allowed to survive to old age before being taken.
Rabbit grazing leaves a graze-line on shrubs, and consume any palatable plants below that height, e.g. seedlings.
Environmental regeneration following the release of biological controls for rabbits have been reviewed by Finlayson, Cooke & Taggart (in press). Their Assessment of Biological Controls and Total grazing pressure – Koonamore provide evidence of the unseen losses caused by European wild rabbits.
A 1952 report noted the vigorous growth of native grasses and a fear that regenerating native pines (Callitris) would become a problem due to their density in the NSW Riverina.
There was a brief (6-7 year) period of regeneration for sheoaks (Allocasuarina verticillata) in the Coorong National Park, before rabbit numbers increased and once again consumed every single seedling.
Following the release of European rabbit fleas (a vector to assist transmission of myxomatosis):
Kangaroo grass (Themedaaustralis) and spear grass (Austrostipa spp) were more prolific along the eastern Mount Lofty Ranges and hairy-nosed wombats (Lasiorhinus latifrons) expanded their distribution from the western banks of the Murray River into the foothills of the Ranges.
Following the release of RHDV:
Widespread regeneration was reported in the arid zone with native grasses and forbs, trees and shrub species flourishing, including native pine (Callitris glaucophylla), needlebush (Hakea leucoptera), umbrella wattle (Acacia ligulata), witchetty bush ( kempeana) and twin-leaved emu bush (Eremophila oppositifolia).
Years later it was concluded the regenerations led to a resurgence of many native animals. The analysis of satellite data confirmed that in areas noted for a resurgence in native animals there was a sharp increase in the annual rate of accumulation of natural vegetation cover following the spread of RHDV.
However, RHDV alone was insufficient to create optimal conditions. Areas near Roxby Downs where cattle were removed, but low post-RHDV rabbit populations survived, had lower rates of recruitment of mulga (Acacia aneura), silver cassia (Senna artemisioides) and sandhill wattle (Acacia ligulata), than did nearby areas where rabbits and other invasive species had also been removed.
A study in Arcoona Creek (Flinders Ranges National Park) found that, despite substantial reductions in rabbit density due to bio-controls, not only did rabbit grazing prevent mulga (Acacia aneura) regeneration, it caused species decline with 40% mortality in a six month period (West, 2008).
The biological controls discussed above (especially the viruses) have the advantages of being relatively self-disseminating, spreading across property boundaries without requiring intervention by land managers.
Rabbit grazing denudes vegetation and prevents the regeneration of palatable species.
Cox T, Strive T, Mutze G, West P & Saunders G. (2013) ‘Benefits of Rabbit Biocontrol in Australia.’ Invasive Animals CRC, Canberra.
Finlayson G, Taggart P & Cooke B (2021) ‘Recovering Australia’s arid-zone ecosystems: learning from continental-scale rabbit control experiments.’ Restoration Ecology. The Journal of the Society for Ecological Restoration. https://doi.org/10.1111/rec.13552
Peacock D, Cox T, Strive T, Mutze G, West P & Saunders P. (2021) ‘Benefits of Rabbit Biocontrol in Australia: An Update.’ Centre for Invasive Species Solutions. Canberra West P (2008) ‘Assessing Invasive Animals in Australia.’ National Land & Water Resources Audit, Canberra
Palatable perennial shrubs were denuded in many semi-arid areas during historic pastoral development – but destocking is not sufficient for their recovery if rabbits persist.
As an example, a 390 hectare livestock exclusion was established at the Koonamore Vegetation Reserve, in South Australia’s pastoral zone, with little measurable recovery in fifty years. When rabbits were then eliminated, the subsequent twenty six years saw the recovery of many perennial species including Acacia aneura, Eremophila mitchellii and Maireana astrotricha.
Koonamore Vegetation Reserve. 1928 to 2018 comparison. Vegetation didn’t respond dramatically until rabbits were removed.
References:
Mutze G (2016) ‘Barking up the wrong tree? Are livestock or rabbits the greater threat to rangeland biodiversity in southern Australia?’ The Rangeland Journal 38(6) DOI:10.1071/RJ16047
Sinclair, R. (2005). Long-term changes in vegetation, gradual and episodic, on the TGB Osborn Vegetation Reserve, Koonamore, South Australia (1926–2002). Australian Journal of Botany, 53, 283-296. https://doi.org/10.1071/BT04144
Sinclair, R & Facelli JM (2018) ‘Ninety years of change on the TGB Osborn Vegetation Reserve, Koonamore: a unique research opportunity’. The Rangeland Journal 41(3) 185-187 https://doi.org/10.1071/RJ18022
Biological controls have proven extremely effective in drastically reducing rabbit populations in Australia. They have led to a resurgence of native vegetation and native animals over immense areas in what must be amongst the greatest conservation programs in Australia. However, as successful as they have been, they may not reduce rabbit populations to the level needed for all plant species to regenerate (less than 1 rabbit/2 hectares), and they may only provide a ‘window’ of time (measured in decades) before their effectiveness wanes.
Biological controls are more effective when combined with physical control techniques, like warren destruction. (Source: ‘Rabbits to Ruin’ pamphlet. Primary Industries SA & Dept of Environment & Natural Resources)
Rabbits graze preferred species first. They can destroy seedlings and prevent plant recruitment.
Two conclusions, summarised by Bird et al (2012), keep recurring in the literature about rabbits grazing native vegetation:
Seedling recruitment might be prevented by rabbits at densities so low that the presence of rabbits, let alone their effect on seedling survival, is barely noticeable to land managers.
Biological controls have been incredibly effective in lowering rabbit numbers and stimulating regeneration – but existing biological controls alone will not reduce rabbit numbers to the level where all plant species will successfully regenerate. Biological controls need supplementing by physical controls.
Bird P, Mutze G, Peacock D & Jennings S (2012) ‘Damage caused by low-density exotic herbivore populations: the impact of introduced European rabbits on marsupial herbivores and Allocasuarina and Bursaria seedling survival in Australian coastal shrubland.’ Biological Invasions 14, 743-755
Cooke BD. (1988) ‘The effects of rabbit grazing on regeneration of sheoaks, Allocasuarina verticillata, and saltwater ti-trees, Melaleuca halmaturorum, in the Coorong National Park, South Australia’. Aust. J. Ecol. 13:11-20.
Cooke B, McPhee S & Hart Q. ‘ A threat to conservation & natural resource management. How to rapidly assess a rabbit problem and take action.’ Bureau of Rural Sciences, Canberra, with AWI & MLA
Cox T, Strive T, Mutze G, West P & Saunders G. (2013) ‘Benefits of Rabbit Biocontrol in Australia.’ Invasive Animals CRC, Canberra.
Finlayson G, Taggart P & Cooke B (2021) ‘Recovering Australia’s arid-zone ecosystems: learning from continental-scale rabbit control experiments.’ Restoration Ecology. The Journal of the Society for Ecological Restoration. https://doi.org/10.1111/rec.13552
Forsyth DM, Scroggie MP, Arthur AD, Lindeman M, Ramsey DSL, McPhee SR, Bloomfield T, and Stuart IG. (2015) ‘Density-dependent effects of a widespread invasive herbivore on tree survival and biomass during reforestation’. Ecosphere 6(4):71. http://dx.doi.org/10.1890/ES14-00453.1
Lange RT & Graham CR. (1983) ‘Rabbits and the failure of regeneration in Australian arid zone Acacia.’ Aust. J. Ecol. 8:377-381.
Mutze G (2016) ‘Barking up the wrong tree? Are livestock or rabbits the greater threat to rangeland biodiversity in southern Australia?’ The Rangeland Journal 38(6) DOI:10.1071/RJ16047
Mutze, J., Cooke, B. and Jennings, S. (2016a). Density-dependent grazing impacts of introduced European rabbits and sympatric kangaroos on Australian native pastures. Biological Invasions, 18, 2365–2376.
Mutze, G., Cooke, B. and Jennings, S. (2016b). Estimating density-dependent impacts of European rabbits on Australian tree and shrub populations. Australian Journal of Botany, 64, 142 – 152.
NSW Scientific Committee (2002) NSW Threatened Species Conservation Act ‘Competition and grazing by the feral European rabbit – Final Determination’.
Peacock D, Cox T, Strive T, Mutze G, West P & Saunders P. (2021) ‘Benefits of Rabbit Biocontrol in Australia: An Update.’ Centre for Invasive Species Solutions. Canberra
Sinclair, R. (2005). Long-term changes in vegetation, gradual and episodic, on the TGB Osborn Vegetation Reserve, Koonamore, South Australia (1926–2002). Australian Journal of Botany, 53, 283-296. https://doi.org/10.1071/BT04144
West P (2008) ‘Assessing Invasive Animals in Australia.’ National Land & Water Resources Audit, Canberra
Competition
As native vegetation flourishes following the control of rabbits, so to do native fauna. Conversely, when rabbits thrive vegetation declines, and so do native fauna. The relationship is especially strong in herbivores competing for similar feed, such as small marsupials with limited foraging ranges. Rabbits may change the vegetation so it no longer suits other species, out-compete them for food, or affect the availability of shelter and nesting sites through vegetation loss or competition.
Examples of harm through competition for food or shelter with rabbits come from Red Kangaroos, Burrowing bettongs, the Greater bilby, and Assessments of Competition links below.
An early example of competition is provided by the red kangaroo (Macropus rufus). In South Australia in the 1870s there were reports of both red kangaroos and rabbits being numerous. However, in 1891 kangaroo numbers had declined to the point of needing an annual six-month moratorium on hunting, while rabbit populations grew. Only a small kangaroo leather industry survived. In 1950, just prior to the release of myxomatosis, it was reported that red kangaroos were probably extinct in north-west Victoria.
In the mid-1950s, soon after the release of myxomatosis, large populations of red kangaroos were reported in the Olary / Broken Hill area of SA and NSW. The commercial kangaroo harvesting industry was revived, and still continues.
Other factors besides rabbit numbers may also be at play, (such as hunting pressure, pastoral management and stock waters), but the inverse relationship between rabbits and red kangaroos has been demonstrated in trials as well, finding that red kangaroo numbers increase when rabbit abundance is heavily reduced. The critical density for rabbits before kangaroos increased was 0.5 rabbits/hectare (1 rabbit : 2 hectares), the same as observed as necessary for the restoration of native grasses in semi-arid areas (and equating to consumption of 15% of the available pasture) – indicating the possibility of direct competition for grasses and forbs.
Red kangaroos are out-competed for feed by rabbits. (Image: Day P)
References:
Finlayson G, Taggart P & Cooke B (2021) ‘Recovering Australia’s arid-zone ecosystems: learning from continental-scale rabbit control experiments.’ Restoration Ecology. The Journal of the Society for Ecological Restoration. https://doi.org/10.1111/rec.13552
Burrowing bettongs (Bettongia lesueur) are similar in size to rabbits and live in large warrens like rabbits, but are less aggressive, and are now extinct on the mainland of Australia, except for protected areas into which they are being re-introduced. Their demise was predicted in a 1924 report because they were unable to recover from drought as quickly as rabbits, who simply overtook their domain and food. The prediction is in line with later ecological thinking that many species survive drought in the most favourable refuge areas available, then disperse from those when better conditions prevail, and the breeding capacity of rabbits enables them to disperse first.
Rabbits hae been reported to evict bettongs from their warrens and, in an enclosure, to even kill them. However other reports suggest the two species were also observed to share warrens.
Besides direct competition rabbits also changed the environment where burrowing bettongs lived. In relatively un-grazed areas of the Riverina (NSW) the dominant tree species, weeping myall (Acacia pendula), co-exists with an understory of creeping saltbush (Rhagodia spinescens), and ruby saltbush (Enchylaena tomentosa). In similar areas grazed by sheep and rabbits, the understory is dominated by corrugated sida (Sida corrugata).
Studies in semi-arid South Australia have found that ruby saltbush was an important resource for burrowing bettongs during droughts, but corrugated sida was not eaten at all by bettongs. Rabbit-induced changes in vegetation would have severely disadvantage burrowing bettongs during drought.
References:
Coman, B.J. (1996) ‘Environmental impact associated with the proposed use of rabbit calicivirus disease for integrated rabbit control in Australia.’ Prepared for the Australia and New Zealand Rabbit Calicivirus Program.
Moore (1953 a) The vegetation of the South-eastern Riverina New South Wales. I. The climax communities. Australian Journal of Botany1(3) 485 – 547
Moore, C.W.E. (1953 b) The vegetation of the South-eastern Riverina New South Wales. II. The disclimax communities. Australian Journal of Botany1, 548–567.
Munro, N.T., Moseby, K.E. and Read, J.L. (2009). The effects of browsing by feral and re-introduced native herbivores on seedling survivorship in the Australian rangelands. The Rangeland Journal, 31, 417–426
Pavey C (2006) ‘Threatened species of the Northern Territory. Burrowing Bettong (inland species) Bettongia lesueur graii.’ Northern Terittory Government
Rolls, E.C. (1969) ‘They all ran wild.‘ Angus & Robertson, Sydney.
The greater bilby (Macrotis lagotis) is a small marsupial from Australia’s bandicoot family. It has strong forelimbs and claws which are used for burrowing and digging up food. Each bilby can have up to twelve burrows in their home range – which they move between in response to food availability. Males are much larger than the females and can be up to 2.5 kg in weight.
Bilbies have very good senses of smell and hearing, and retreat to their burrows if alarmed. They feed on insects (e.g. termites, ants, grasshoppers and beetles), butterfly and moth larvae (e.g. witchetty grubs), spiders, seeds (which are licked up by their long, slender tongues), fruit, bulbs and fungi which they dig up.
European wild rabbits reduce the cover provided by native vegetation, prevent the natural regeneration of many plant species, and compete with bilbies for food and burrows. Bilbies are ejected from their burrows by rabbits. A Rabbit Inspector at Hay (NSW) in the 1800s noted the take-over of bilby burrows by the more aggressive rabbits and reported that within a few decades the bilbies disappeared and the ‘whole countryside swarmed with rabbits.’
Wild rabbits are also food for feral cats and foxes, sustaining the populations of predators and hence maintaining increased predation on bilbies.
Once occurring throughout much of Australia, bilbies can now only be found where rabbits are less common. The control of rabbits is fundamental to the survival or bilbies.
For more information, see Witchetty grubs and bilbies under ‘Ecological disruption’ and the Easter Bilby fact sheet.
References:
ANCA – Greater Bilby Recovery Team (1995) ‘ Australia’s threatened plants and animals.’ Australian Nature Conservation Agency. Canberra.
Coman, B.J. (1996) ‘Environmental impact associated with the proposed use of rabbit calicivirus disease for integrated rabbit control in Australia. Draft.’ Prepared for the Australia & New Zealand Calivirus Program.
Greater Bilby National Recovery Team (2019) ‘Recovery Plan for the Greater Bilby—DRAFT.’ Commonwealth of Australia.
Pavey, C. (2006). ‘National Recovery Plan for the Greater BilbyMacrotis lagotis’. Northern Territory Department of Natural Resources, Environment and the Arts.
Rolls, E.C. (1969) ‘They all ran wild.‘ Angus & Robertson, Sydney
Strahan R. (ed) (1995) ‘The Mammals of Australia.’ Australian Museum. Reed Books, Chatsworth NSW pg756.
Assessments of the benefits of the release of European rabbit fleas to bolster the spread of myxomatosis have concluded it contributed to the spread of swamp wallabies (Wallabia bicolor) and red-necked wallabies (Macropus rufogriseus) in western Victoria and south-east SA. The conclusion was supported by research in the area showing the abundance of western grey kangaroos (Macropus fuliginosus) and common wombats (Vombatus ursinus) increased following the physical removal of rabbits – but stayed low where rabbits had not been controlled. Red kangaroos (Macropus rufus) and euros (Macropus robustus) have recolonised areas following rabbit control indicating that they also suffer from competition by rabbits.
A scientific panel in NSW identified threatened species that suffer from competition with rabbits, including the Yellow-footed Rock-wallaby (Petrogale xanthopus), Brush-tailed Rock-wallaby (Petrogale penicillatae) and Southern Hairy-nosed Wombat (Lasiorhinus latifrons). The Plains Wanderer (Pedionomus torquatus) and Malleefowl (Leipoa ocellata) also appear to be adversely affected by rabbits, through competition for food and/or by alteration and reduction of suitable habitat.
An assessment of the impact of calicivirus disease added stick nest rats, black wallabies, Eyrean grass wrens, and Gould’s petrel to the list of native animals documented as threaened by competition from rabbits,
Coman B.J. (1996) ‘Environmental impact associated with the proposed use of rabbit calicivirus disease for integrated rabbit control in Australia.‘ Prepared for the Australian & New Zealand Calicivirus Program.
Finlayson G, Taggart P & Cooke B (2021) ‘Recovering Australia’s arid-zone ecosystems: learning from continental-scale rabbit control experiments.’ Restoration Ecology. The Journal of the Society for Ecological Restoration. https://doi.org/10.1111/rec.13552
NSW Scientific Committee (2002) NSW Threatened Species Conservation Act ‘Competition and grazing by the feral European rabbit – Final Determination’.
In areas where historic grazing pressure changed the landscape the continued presence of rabbits can hold it in a degraded (early successional) state, regardless of improved stock management and efforts to rehabilitate the landscape. Attempts to reintroduce native animals may fail due to this or there may be insufficient feed to keep them in breeding condition – i.e. they may survive but not be fit enough to breed (Finlayson, Cooke & Taggart).
Competition for burrows by more aggressive rabbits was a contributing factor to the extinction of the lesser bilby (Macrotis leucura) and the lesser stick-nest rat (Leporillus apicalis), and it is believed that rabbits may have been responsible for significant declines in the night parrot (Geopsittacus occidentalis) through habitat degradation. There is also evidence of rabbits acting aggressively towards native mammals to protect resources, even much larger ones like yellow-footed rock wallabies (Petrogale xanthopus) (Dept of the Env & Energy, 2016).
ANCA – Greater Bilby Recovery Team (1995) ‘ Australia’s threatened plants and animals.’ Australian Nature Conservation Agency. Canberra.
Coman, B.J. (1996) ‘Environmental impact associated with the proposed use of rabbit calicivirus disease for integrated rabbit control in Australia. Draft.’ Prepared for the Australia & New Zealand Calivirus Program.
Finlayson G, Taggart P & Cooke B (2021) ‘Recovering Australia’s arid-zone ecosystems: learning from continental-scale rabbit control experiments.‘ Restoration Ecology. The Journal of the Society for Ecological Restoration. https://doi.org/10.1111/rec.13552
Greater Bilby National Recovery Team (2019) ‘Recovery Plan for the Greater Bilby—DRAFT.’ Commonwealth of Australia.
Moore (1953 a) The vegetation of the South-eastern Riverina New South Wales. I. The climax communities. Australian Journal of Botany1(3) 485 – 547
Moore, C.W.E. (1953 b) The vegetation of the South-eastern Riverina New South Wales. II. The disclimax communities. Australian Journal of Botany1, 548–567.
Munro, N.T., Moseby, K.E. and Read, J.L. (2009). The effects of browsing by feral and re-introduced native herbivores on seedling survivorship in the Australian rangelands. The Rangeland Journal, 31, 417–426
Pavey C (2006) ‘Threatened species of the Northern Territory. Burrowing Bettong (inland species) Bettongia lesueur graii.’ Northern Terittory Government
Pavey, C. (2006). ‘National Recovery Plan for the Greater BilbyMacrotis lagotis’. Northern Territory Department of Natural Resources, Environment and the Arts.
NSW Scientific Committee (2002) NSW Threatened Species Conservation Act ‘Competition and grazing by the feral European rabbit – Final Determination’.
Rolls, E.C. (1969) ‘They all ran wild.‘ Angus & Robertson, Sydney
Strahan R. (ed) (1995) ‘The Mammals of Australia.’ Australian Museum. Reed Books, Chatsworth NSW pg756.
Ecological disruption
As ‘ecosystem engineers’, the changes rabbits cause have consequences well beyond the immediate impacts from consumption and competition. Rabbit-induced changes to vegetation can have far-reaching impact, affecting other animals and whole environmental communities. Witchetty grubs and bilbies, Glossy Black-Cockatoos, and Native rodents below provide examples.
The ecology of the witchetty bush (Acacia kempeana) provides an example of complex problems caused by rabbits. Witchetty bush is a shrub or tree found in arid areas of Australia, especially WA, SA and the NT, but also in Qld and NSW. It grows up to 5 metres, but is slow growing given the low and erratic rainfall throughout its distribution.
Large Cossid moths (Endoxyla spp) lay eggs under the trees and the larvae (Witjuti or witchetty grubs) feed on the sap of the Acacia roots. The grubs are tucker for Indigenous people and a favourite of the greater bilby (Macrotis lagotis). Edible gum and seeds are also sourced from the trees, as is bush medicine and wood for spears. The plants also support birds (nesting and foraging), insects (galls and pollinators), and ants (seed harvesters) – as well as any bilbies dining on the witchetty grubs.
There is very little regeneration of witchetty bushes in areas where rabbits co-exist, and it can take 10-20 years before they are tall enough to be safe from destruction by rabbits. In the presence of rabbits the incidence of the trees declines and the average age rises. Several decades of effective rabbit control would be required for regenerating plants to be safe from renewed rabbit grazing pressure.
The Birriliburu Indigenous Protected Area in WA is free of rabbits and still supports witchetty bush and bilbies in the wild.
Witchetty grubs are dug up and eaten by bilbies. (Image: Alan Yen, ABC News)
References:
Commonwealth of Australia (2019) ‘Recovery Plan for the Greater Bilby – DRAFT’.
The Glossy Black-Cockatoo (Calyptorhynchus lathami) is one of Australia’s rarest cockatoos. The lathami sub-species is listed as vulnerable in NSW and Qld and threatened in Victoria. The halmaturinus sub species is endangered in SA. Their diet is highly specialised, focused on seeds from sheoaks, and their nesting preference is hollows in very old trees. Their close relatives, the red-tailed black-cockatoos, also have a fairly narrow diet, preferring seeds from brown stringybark (Eucalyptus baxteri), desert stringybark (Eucalyptus arenacea) and buloke (Allocasuarina luehmannii).
Glossy-black cockatoo (KI) (Image: SA Gov, DEW)
Calyptorhynchus lathami originally occurred in the Mount Lofty Ranges and Kangaroo Island, as did its primary food source, the drooping sheoak (Allocasuarina verticillata). Selective clearance of the sheoaks (for firewood and drought forage) destroyed the habitat of the glossy blacks and, on the mainland, selective grazing by rabbits prevented regeneration of the trees. Only on rabbit-free Kangaroo Island, where sheoaks persist and seedlings can grow free from rabbit grazing, do the birds still survive. A recovery program, involving tree planting and provision of nesting boxes, is proving successful as the population of glossy black-cockatoos gradually increases.
References:
Joseph L (1989) ‘The Glossy Balck Cockatoo in the south Mt Lofty Ranges’ SA Ornithologist 30
Natural Resources Kangaroo Island (2017) ‘Glossy Black-cockatoo Recovery Program. Funding prospectus 2017-20’ KI NRB Board & DEWNR
A 2016 report documented major expansions in the distribution of three native rodents – the dusky hopping-mouse (Notomys fuscus), spinifex hopping-mouse (Notomys alexis) and the plains mouse (Pseudomys australis) – and a small marsupial carnivore, (the crest-tailed mulgara (Dasycercus cristicauda)), over massive areas of inland Australia. The expansion was attributed to improved habitat, reduced predation, and greater availability of prey – all due to the introduction of RHDV in 1995 and the subsequent reduction in rabbit numbers (Pedlar et. al., 2016). Another small native rodent, the desert mouse (Pseudomys desertor), was recorded at Innamincka for the first time ever during this time.
The expansion of dusky hopping-mice had been noticed in 2006 and studies concluded the spread was due to excellent recent rainfall, in combination with reduced predation and improved plant cover as a result of reduced rabbit numbers following RHDV. In drier times since then, dusky hopping-mice retreated to ‘refuge areas’ (sites with favourable conditions, from which they may once again expand when conditions are favourable). The refugia are much further south than their pre-RHDV distribution (Finlayson, Cooke & Taggart).
Predictions that the native rodents would rebound from those refuge areas in good seasons seem to have been justified, with reports of that occurring across the southern South Australian rangelands following rains in 2021.
Several papers on the diet of barn owls (Tyto delicatula) in north-eastern SA, western NSW, and south-western Queensland generate the impression that in southern rangeland and agricultural areas introduced house mice (Mus musculus) are the dietary mainstay, but native rodents and dasyurids are more common in the north. The number of native rodent and dasyurid species present in owl faecal pellets is increasing, adding to the picture of resurgent populations since the RHDV-induced reduction in rabbit numbers (Finlayson, Cooke & Taggart).
References:
Finlayson G, Taggart P & Cooke B (2021) ‘Recovering Australia’s arid-zone ecosystems: learning from continental-scale rabbit control experiments.’ Restoration Ecology. The Journal of the Society for Ecological Restoration. https://doi.org/10.1111/rec.13552
Pedlar RD, Brandle R, Read JL, Southgate R, Bird P & Moseby KE. (2016) ‘Rabbit biocontrol and landscape-scale recovery of threatened desert mammals.’ Conservation Biology Vol30, Issue 4 https://doi.org/10.1111/cobi.12684
As a food source, rabbits also sustain populations of feral predators. See Promoting Predators.
Finlayson G, Taggart P & Cooke B (2021) ‘Recovering Australia’s arid-zone ecosystems: learning from continental-scale rabbit control experiments.’ Restoration Ecology. The Journal of the Society for Ecological Restoration. https://doi.org/10.1111/rec.13552
Natural Resources Kangaroo Island (2017) ‘Glossy Black-cockatoo Recovery Program. Funding prospectus 2017-20’ KI NRB Board & DEWNR
Peacock D, Cox T, Strive T, Mutze G, West P & Saunders P. (2021) ‘Benefits of Rabbit Biocontrol in Australia: An Update.’ Centre for Invasive Species Solutions. Canberra West P (2008) ‘Assessing Invasive Animals in Australia.’ National Land & Water Resources Audit, Canberra
Pedlar RD, Brandle R, Read JL, Southgate R, Bird P & Moseby KE. (2016) ‘Rabbit biocontrol and landscape-scale recovery of threatened desert mammals.’ Conservation Biology Vol30, Issue 4 https://doi.org/10.1111/cobi.12684
Promoting Predators
Rabbits, at different stages of life, are preyed upon by some mammals, birds and reptiles – to differing degrees. For some predators (feral cats and foxes), rabbits may be an important part of their diet; for others they may only be an opportunistic or incidental feed. The relationships may vary with seasons and their relative abundance.
By sustaining populations of feral predators, rabbits indirectly increase the predation by those species on native animals. This is termed ‘hyper-predation’. Rabbit-induced hyper-predation by cats and foxes has been linked to the extinction and decline of conilurine rodents (Muradae), the biggest and most diverse group of Australian rodents, including Notomys and Pseudomys.
Examples of rabbit-predator interactions are provided by Feral cats, Dingoes, Wedge-tailed eagles and Critical Weight Range terrestrial animals.
Feral cats are a significant threat to many native fauna and they readily take rabbits as well. In some cases predation by cats (Felis catus) and foxes (Vulpes vulpes) may supress rabbit numbers, but high rabbit numbers following successful breeding enable them to escape from predator control. By ‘harvesting’ mature rabbits from the field, but not taking burrow-bound kittens, feral cats may in effect be farming rabbits as the young mature and venture above ground. In any event it is evident that rabbits help sustain populations of feral predators, and hence the pressure they exert on native prey animals.
An observed seasonal influence is the drop in rabbit, cat and fox numbers during drought. Immediately following drought, the breeding capacity of rabbits enables them to quickly rebound and escape predator control, resulting in resource degradation through over-grazing and a subsequent population crash. Predators consume starving rabbits but soon turn to carrion and other fauna (termed prey switching), before their numbers also drop. The situation differs following the introduction of new biological controls as rabbit numbers do not quickly rebound and drive a resurgence in predator populations – and hence there are no additional prey-switching events (Finlayson, Cooke & Taggart).
A comparison of cat behaviour between a site where rabbits were removed and a control where they remained present showed a 40% drop in cat numbers within a month of rabbit removal, and a shift in the diet of the survivors to include more carrion, small native reptiles and insects – but no increase in predation of native rodents. In the long term, the reduced number of cats offset any losses due to prey-switching (Finlayson, Cooke & Taggart).
Observers believe that feral cats are less likely to take poisoned baits when rabbits are abundant. Rabbit control is a useful first stage for feral cat control programs.
References:
Finlayson G, Taggart P & Cooke B (2021) ‘.’ Restoration Ecology. The Journal of the Society for Ecological Restoration. https://doi.org/10.1111/rec.13552
Holden C & Mutze G (2002) ‘Impact of rabbit haemorrhagic disease on introduced predators in the Flinders Rangers, South Australia.’ Wildlife Research. 29: 615-626
McGregor H, Moseby K, Johnson CN & Legge S. (2019) ‘The short-term response of feral cats to rabbit population decline: Are alternative native prey more at risk?’ Biol Invasions 22, 799-811 https://doi.org/10.1007/s10530-019-02131-5
Mutze, G. (2017) ‘Continental-scale analysis of feral cat diet in Australia, prey-switching and the risk:benefit of rabbit control.‘ Journal of Biogeography. Vol 44, Issue 7.
Like rabbits, dingoes were introduced to Australia by humans – probably between 5 -10,000 years ago – but the wild dogs have now ‘naturalised’ and are seen by many as part of the Australian environment. When rabbits were introduced and spread through much of Australia, they became an important part of the diet of dingoes.
Dingo diet varies with seasons and prey availability. Across Australia almost 75% of their prey is mammalian, followed by birds (nearly 20%), and reptiles. Their prey is typically in the 0.5 – 15kg weight range, including kangaroos, wallabies, possums, wombats and rabbits. They are skilled hunters but also scavenge on carcasses. Packs of dingoes are more likely to target bigger prey, like kangaroos, while solitary dingoes hunt small to medium sized prey. It has been reported that dingo predation alone can depopulate local hopping-mice within a few months.
A seven-year study in arid Australia followed the diet of dingoes from a period of abundance following good rains to a subsequent drought. Smaller, easily caught animals (like rodents) were popular when abundant after the rains, but as conditions dried in-take shifted to larger animals (like kangaroos and cattle – the latter increasingly available as carcases when drought set in). Rabbits were consistently just over 50% of dingo prey. It was concluded that ‘catchability’ and ‘accessibility’ were more important than numbers or biomass in determining the prey consumed.
From the early days of pastoralism rabbit plagues occurred in areas with high dingo numbers. Rabbits were no doubt a big part of their diet and most likely were beneficial to them, but dingoes alone couldn’t contain rabbit populations. In good seasons the reproductive capacity of rabbits exceeded the capacity of dingoes and other predators to hunt and kill them.
When calicvirus arrived in pastoral regions it drastically reduced rabbit numbers and their breeding capacity, apparently to the extent that predators like dingoes then had more influence on total rabbit numbers. It seems predators can contain rabbit populations when the prey are under stress (e.g. from disease or drought) and in relatively low numbers, but when conditions are better and rabbits are numerous they out-breed the pressure from predators, and may help sustain them.
References:
Allen BL, Leung LK-P (2012) Assessing Predation Risk to Threatened Fauna from their Prevalence in Predator Scats: Dingoes and Rodents in Arid Australia. PLoS ONE 7(5): e36426. https://doi.org/10.1371/journal.pone.0036426
Cooke, B. D., & Soriguer, R. C. (2017). ‘Do dingoes protect Australia’s small mammal fauna from introduced mesopredators? Time to consider history and recent events.’ Food Webs, 12, 95-106. https://doi.org/10.1016/j.fooweb.2016.04.002
Corbett LK & Newsome AE (1987) ‘The feeding ecology of the dingo : III. Dietary relationships with widely fluctuating prey populations in arid Australia: an hypothesis of alternation of predation.’ Oecologia, 1987 Dec;74(2):215-227. doi: 10.1007/BF00379362
Kerle A (2020) ‘Notice of and reasons for the Final Determination. The cascading effects of the loss or removal of dingoes from New South Wales landscapes.’ NSW Threatened Species Scientific Committee.
Mattias CR Oskarsson et al., (2011) ‘Mitochondrial DNA data indicate an introduction through Mainland South East Asia for Australian dingoes and Polynesian domestic dogs’, in Proceedings of the Royal Society: Biological Sciences, p. 2, doi:10.1098/rspb.2011.1395, online 7 September 2011.
Pech, R. P., Sinclair, A. R. E., Newsome, A. E., and Catling, P. C. (1992). ‘Limits to predator regulation of rabbits in Australia: evidence from predator-removal experiments’. Oecologia 89, 102-112.
Wedge-tailed eagles will take rabbits and eat carcases. (Image: Day P)
Wedge-tailed eagles (Aquilla audax), and birds like the black-breasted buzzard (Hamirostra melanosternon), are known to include rabbits in their diet and it has been speculated that they may suffer when rabbits are not available. However a study of changes following the introduction of RHDV showed that while it led to a 85% reduction in rabbit numbers, and an increase in large varanid lizards (like goannas), eagle (and other raptor) numbers remained steady. Nor was there any sudden decrease in egg clutch size or fledgling survival rates. Their diet exploited an increased abundance of native prey like kangaroos.
References:
Edwards, G.P., Dobbie, W. and Berman D. McK. (2002). Population trends in European rabbits and other wildlife of central Australia in the wake of rabbit haemorrhagic disease. Wildlife Research 29(6) 557 – 565.
Olsen, J., Cooke, B., Trost, S. and Judge, D. (2014). Is wedge-tailed eagle, Aquila audax, survival and breeding success closely linked to the abundance of European rabbits, Oryctolagus cuniculus?. Wildlife Research. 41, 95. 10.1071/WR14033.
Steele, W. and Baker-Gabb, D. (2009). A national community-based survey of the diurnal birds of prey (BOPWatch). Boobook 27, 23-24.
The high rate of decline and extinction of small to medium sized Australian mammals prior to the mid twentieth century has led to a conclusion that terrestrial mammals in the 35 – 5,500 g weight range (termed the Critical Weight Range – CWR) have been at most risk of extinction. The weight range includes anything from a native mouse to a rock wallaby, though in arid areas smaller animals can be very fast breeders and may be faster and harder to catch than larger prey.
Small to medium sized terrestrial animals have faced predation by feral cats and foxes, and been exposed as plant cover was reduced by introduced herbivores (including rabbits). Degradation of vegetation would also have affected their food sources, and some would have experienced direct competition for food and burrows from rabbits (which at 1,600 g are within the critical weight range), exacerbating the pressure from predators.
References:
Chisholm R & Taylor R (2007) ‘Null-Hypothesis Significance Testing and the Critical Weight Range for Australian Mammals’. Conservation Biology Volume 21, No. 6, 1641–1645. DOI: 10.1111/j.1523-1739.2007.00815.x
Johnson, C.N. and Isaac, J.L. (2009) Body mass and extinction risk in Australian marsupials: the ‘critical weight range revisited’. Austral Ecology, 34, 35–40.
Rabbits are in the critical weight range for cats and foxes – they are the most preferred size for prey, offering good sustenance for the energy expended in hunting. Different animals have different hunting preferences. This is likely to be one factor why feral cat numbers decline when rabbit numbers do, but wedge-tailed eagle populations do not. Rabbit control is especially beneficial to native fauna outside the critical ‘small to medium size’ weight range for cats and foxes; e.g. kangaroos are larger. Although brush-tailed and crest-tailed mulgaras (Dasycercus spp) are within the critical weight range, they have prospered from rabbit control due to the improvement in ecological condition.
In summary, most evidence suggests that:
As rabbits decline, so too does the number of feral predators (cats and foxes, which are such a threat to many native fauna).
Vegetation flourishes – leading to a resurgence of native fauna.
There may be some prey switching by native predators as a consequence of rabbit decline, but the resurgence of plants and other fauna minimises or over-rides any losses for a good nett outcome.
To minimise the risk of temporary prey-switching affecting native fauna, programs to control pest predators should accompany rabbit-control initiatives. For optimum effectiveness, feral cat control programs should start with rabbit control.
Allen BL, Leung LK-P (2012) Assessing Predation Risk to Threatened Fauna from their Prevalence in Predator Scats: Dingoes and Rodents in Arid Australia. PLoS ONE 7(5): e36426. https://doi.org/10.1371/journal.pone.0036426
Chisholm R & Taylor R (2007) ‘Null-Hypothesis Significance Testing and the Critical Weight Range for Australian Mammals’. Conservation Biology Volume 21, No. 6, 1641–1645. DOI: 10.1111/j.1523-1739.2007.00815.x
Cooke, B. D., & Soriguer, R. C. (2017). ‘Do dingoes protect Australia’s small mammal fauna from introduced mesopredators? Time to consider history and recent events.’ Food Webs, 12, 95-106. https://doi.org/10.1016/j.fooweb.2016.04.002
Corbett LK & Newsome AE (1987) ‘The feeding ecology of the dingo : III. Dietary relationships with widely fluctuating prey populations in arid Australia: an hypothesis of alternation of predation.’ Oecologia, 1987 Dec;74(2):215-227. doi: 10.1007/BF00379362
Edwards, G.P., Dobbie, W. and Berman D. McK. (2002). Population trends in European rabbits and other wildlife of central Australia in the wake of rabbit haemorrhagic disease. Wildlife Research 29(6) 557 – 565.
Finlayson G, Taggart P & Cooke B (2021) ‘Recovering Australia’s arid-zone ecosystems: learning from continental-scale rabbit control experiments.’ Restoration Ecology. The Journal of the Society for Ecological Restoration. https://doi.org/10.1111/rec.13552
Holden C & Mutze G (2002) ‘Impact of rabbit haemorrhagic disease on introduced predators in the Flinders Rangers, South Australia.’ Wildlife Research. 29: 615-626
Johnson, C.N. and Isaac, J.L. (2009) Body mass and extinction risk in Australian marsupials: the ‘critical weight range revisited’. Austral Ecology, 34, 35–40.
Kerle A (2020) ‘Notice of and reasons for the Final Determination. The cascading effects of the loss or removal of dingoes from New South Wales landscapes.’ NSW Threatened Species Scientific Committee.
Mattias CR Oskarsson et al., (2011) ‘Mitochondrial DNA data indicate an introduction through Mainland South East Asia for Australian dingoes and Polynesian domestic dogs’, in Proceedings of the Royal Society: Biological Sciences, p. 2, doi:10.1098/rspb.2011.1395, online 7 September 2011.
McGregor H, Moseby K, Johnson CN & Legge S. (2019) ‘The short-term response of feral cats to rabbit population decline: Are alternative native prey more at risk?’ Biol Invasions 22, 799-811 https://doi.org/10.1007/s10530-019-02131-5
Mutze, G. (2017) ‘Continental-scale analysis of feral cat diet in Australia, prey-switching and the risk:benefit of rabbit control.‘ Journal of Biogeography. Vol 44, Issue 7.
Olsen, J., Cooke, B., Trost, S. and Judge, D. (2014). Is wedge-tailed eagle, Aquila audax, survival and breeding success closely linked to the abundance of European rabbits, Oryctolagus cuniculus?. Wildlife Research. 41, 95. 10.1071/WR14033.
Pech, R. P., Sinclair, A. R. E., Newsome, A. E., and Catling, P. C. (1992). ‘Limits to predator regulation of rabbits in Australia: evidence from predator-removal experiments’. Oecologia 89, 102-112.
Steele, W. and Baker-Gabb, D. (2009). A national community-based survey of the diurnal birds of prey (BOPWatch). Boobook 27, 23-24.
Soil Disturbance, Carbon & Weeds
Overgrazing of any kind reduces the number of grass, forb and shrub species surviving, reduces plant cover (i.e. leads to more bare ground), depletes soil carbon, and increases the bulk density (amount of compaction) of soil. Controlling rabbits can halt these processes and open opportunities for rehabilitation and improved soil health. One study has estimated that rabbit control in 25% of the mulga woodlands of inland Australia would result in the sequestration of an additional 5-6 megatonnes of CO2 equivalents per year.
Digging and the removal of ground cover by rabbits exposes soil to erosion. (Source: Schulz, G. NSW Govt)
By removing above-ground and below-ground vegetation through grazing and warren construction, rabbits contribute to erosion – the loss of topsoil by wind and rain. That invites ‘early colonisers’ (plants, notably weeds, that colonise bare ground and degraded vegetation), and reduces the chance of successful establishment by native plants – which increases the susceptibility of many native fauna to predation from feral predators.
Heavily grazed areas around rabbit warrens become a haven for weeds. (Image: B Cooke)
Tunnel erosion can be initiated by rabbits in high rainfall areas. (Image: B Coman, 1996)
On-site erosion inevitably contributes to off-site degradation, be it sedimentation of waterways and dams or streambank erosion (with potential to degrade wetlands, or affect water supplies and treatment costs), or dust (resulting in air pollution and health problems, or the blocking of roads or damage to fences). The rate of sedimentation of Burrinjuck, Umberumberka (both in NSW) and Pekina (SA) reservoirs was greatly reduced following the spread of myxomatosis.
The critical rabbit density for the recruitment of many native seedlings is 1 rabbit : 2 hectares, and a similar level triggers a decline in native grasses. Above that density native grasses decline, due to selective grazing pressure, and are replaced by unpalatable introduced weeds adapted to tolerate rabbit browsing. Rabbits also disseminate weeds by spreading undigested weed seeds in their faeces, while the high level of nitrogen in their droppings promotes the growth of some weeds.
Bengsten A & Cox T. (2014) ‘The role of rabbit and other invasive herbivore control in reducing Australia’s greenhouse gas emissions.’ pestSMART, Invasive Animals CRC.
Coman BJ (1996) ‘Environmental impact associated with the proposed use of rabbit calicivirus disease for integrated rabbit control in Australia. Draft’ Prepared for the Australia & New Zealand Calicivirus Program.
Radcliffe F (1938) ‘Flying fox and drifting sand: the adventures of a biologist in Australia’. Angus & Robertson, Sydney.
Ratcliffe, F.N. (1938). Soil drift in the arid pastoral areas of South Australia. CSIRO Pamphlet No 64.
Williams K, Parer I, Coman B, Burley J & Braysher M. (1995) ‘Managing Vertebrate Pests: Rabbits.’ Bureau of Resource Sciences & CSIRO Division of Wildlife & Ecology. Australian Government Publishing Service, Canberra.
