Rabbit Density Research Articles

Does targeted management work for red-legged partridges Alectoris rufa? Twelve years of the ‘Finca de Matallana’ demonstration project

After the implementation of a management package for red-legged partridges (Alectoris rufa) (including habitat improvement, legal predator removal, supplementary feeding and watering and shooting restrain) in an agricultural Mediterranean area of Spain (308 ha), spring pair densities increased from 2.92 to 12.66/km2 in 9 years, together with summer densities (from 24 to 98 birds/km2) and autumn densities (from 16.5 to 86 birds/km2). We recorded an overall decrease in the over-winter survival of partridges and an increase in their over-summer survival as time progressed. Productivity doubled in 5 years and densities of wild rabbits (Oryctolagus cuniculus) significantly increased. Hence, this study shows that a feasible and affordable combination of management tools worked to improve partridge populations, and also helped the recovery of wild rabbits. The study site supported the presence of 42 ‘red-listed’ species (including 21 species of raptors).

A case of low success of blind vaccination campaigns against myxomatosis and rabbit haemorrhagic disease on survival of adult European wild rabbits

Vaccination campaigns against myxomatosis and rabbit haemorrhagic disease (RHD) are commonly used in translocation programs conducted for the purpose of recovering wild European rabbit populations in Iberian Mediterranean ecosystems. In most cases rabbits are vaccinated ‘blind’ (i.e. without assessing their prior immunological status) for economic and logistic reasons. However, there is conflicting evidence on the effectiveness of such an approach. We tested whether blind vaccination against myxomatosis and rabbit haemorrhagic disease improved rabbit survival in a rabbit translocation program where wild rabbits were kept in semi-natural conditions in three enclosures. We conducted nine capture sessions over two years (2008–2010) and used the information collected to compare the survival of vaccinated (n=511) versus unvaccinated (n=161) adult wild rabbits using capture-mark-recapture analysis. Average monthly survival was no different for vaccinated versus unvaccinated individuals, both in the period between release and first capture (short-term) and after the first capture onward (long-term). Rabbit survival was lower in the short term than in the long term regardless of whether rabbits were vaccinated or not. Lower survival in the short-term could be due to the stress induced by the translocation process itself (e.g. handling stress). However, we did not find any overall effect of vaccination on survival which could be explained by two non-exclusive reasons. First, interference of the vaccine with the natural antibodies in the donor population. Due to donor populations have high density of rabbits with, likely, high prevalence of antibodies as a result of previous natural exposure to these diseases. Second, the lack of severe outbreaks during the study period. Based on our findings we argue that blind vaccination of adult rabbits in translocation programs may be often mostly ineffective and unnecessarily costly. In particular, since outbreaks are hard to predict and vaccination of rabbits with natural antibodies is ineffective, it is crucial to assess the immunological status of the donor population before translocating adult rabbits.

Density-dependent grazing impacts of introduced European rabbits and sympatric kangaroos on Australian native pastures

Little information is available on relationships between pest animal density and damage in natural ecosystems. Introduced European rabbits, Oryctolagus cuniculus, cause severe damage to Australian native vegetation but density–damage relationships are largely unexplored. There are no recognized simple methods to estimate their impacts on native pastures, due in part to confusion with grazing impact of other herbivores. We tested simple quantitative sampling methods using multiple small quadrats to detect site differences in pasture cover, pasture species richness and dung pellet density of herbivores, from which rabbit density and relative abundance of larger herbivores were estimated. Native pasture cover and species richness declined exponentially with increasing rabbit density, within the range of 0–5 rabbits ha−1, while cover of unpalatable exotic pasture species increased. By contrast, kangaroo abundance was positively related to palatable native pasture cover and negatively related to cover of unpalatable weeds, and had no negative effect on native pasture cover or species richness that was discernable against a background of low to moderate rabbit densities. Perennial native forbs and perennial grasses replaced invasive Wards weed as the dominant ground cover at low rabbit densities. We conclude that, regardless of previous grazing history, contemporary kangaroo grazing pressure and weed invasion, the severely degraded state of native pastures was perpetuated by rabbits. The effect of rabbits on native pasture can be recorded in a simple manner that is suitable for identifying density–damage relationships in the presence of other herbivores and changes over time. This method is seen as particularly useful in setting target densities below which rabbits must be managed to maintain native plant communities and ecosystem function in southern Australia. It may also be useful to demonstrate rabbits’ impacts in other regions, including optimum densities for plant biodiversity benefits in their native European range.

Optimization and accuracy of faecal pellet count estimates of population size: The case of European rabbits in extensive breeding nuclei

Cost-effective indices to estimate relative abundances of species are crucial for their management and conservation. As an example, population indices are needed to monitor extensive breeding nuclei used for translocating wild rabbit populations. Based on counts of faecal pellets from four high density rabbit nuclei in southwest Spain: (i) we assess the accuracy of this population index in high-density populations; and (ii) present a simulation approach to evaluate how the reduction of the counting effort affects accuracy of the population estimates. Our findings suggest that this method provides a valid estimate in high-density rabbit populations, and, notably, estimates would have not substantially changed after a reduction of 45–65% in the number of counted plots depending on variation on rabbit density between nuclei. We provide a framework that managers and other scientists could use to improve data collection of pellet counts in order to optimize their chances of detecting relative abundance estimates of rabbits. In addition, we present a R function to implement our approach that can easily be applied in a variety of monitoring programmes for other species based on count data. This will likely help to reduce field-effort in different studies without compromising population indices estimates.

Estimating density-dependent impacts of European rabbits on Australian tree and shrub populations

Introduced European rabbits, Oryctolagus cuniculus, can severely damage Australian native vegetation but the problem is difficult to quantify because simple methods to estimate rabbit impacts are lacking. Management decision-making is often uncertain because of unknown relationships between rabbit density and damage. We tested simple quantitative sampling methods using belt transects to detect differences in critical characteristics of perennial vegetation communities affected by rabbit browsing: damage to individual juvenile shrubs and trees, and loss of recruitment cohorts. Rabbit density and relative abundance of larger herbivores were estimated from dung pellet density. The prevalence of identifiable rabbit browse on juvenile plants increased with increasing rabbit density and was higher for plant species considered by previous authors to be highly palatable than for moderately palatable or unpalatable species. At densities of ≥0.5 rabbits ha–1, highly palatable plant species were severely damaged as juveniles and cohorts in 0.3–1.0 m height classes and 5–20 mm basal diameter classes were missing. Similar damage became apparent in moderately palatable species at 2 rabbits ha–1 but was rarely seen in unpalatable species. Within species, size cohort evenness was inversely related to the proportion of surviving juveniles with identifiable rabbit damage. The effect of rabbits on native vegetation condition can be recorded in a simple manner suitable for identifying density-damage relationships and changes in vegetation condition over time. It is particularly useful in setting target densities below which rabbits must be managed to maintain natural plant recruitment and ecosystem function in conservation reserves and pastoral grazing properties of southern Australia.

An assessment of the populations of Sylvilagus brasiliensis andinus in Páramos with different vegetation structures in the northeastern Andes of Ecuador

For the first time in Ecuador, a defecation rate is calculated from three captured páramo rabbit Sylvilagus brasiliensis andinus individuals. Combining this defecation rate, the pellet count method, and Novaro et al.'s (1992) hare density equation, páramo rabbit densities were calculated in four páramo localities with different vegetation structures. A correlation was found between the páramos' vegetation diversity and páramo rabbit densities. This study shows that pellet counting is an economical and non-invasive method that permits the estimation of páramo rabbit abundances in páramo ecosystems. Páramo rabbit abundances may serve as a tool to measure the effects of human activity over small mammal population sizes. Further studies of small páramo mammals will help better understand páramo ecosystem functions and will provide insights into its land management and conservation.

Barking up the wrong tree? Are livestock or rabbits the greater threat to rangeland biodiversity in southern Australia?

Increasing provision of permanent water points has put most Australian pastoral rangelands within grazing distance of sheep, cattle, kangaroos and large feral herbivores, and there is concern that grazing-sensitive native plants will be lost as a result. Proposals have been developed to conserve plant biodiversity by permanently excluding livestock from any areas that are remote from permanent water, or to buy back pastoral properties and remove existing water points to create large reserves. There is, however, little evidence that water-remote areas provide refuge for grazing-sensitive plants, nor consistent evidence of plant biodiversity loss along gradients of increasing livestock grazing pressure in proximity to water. One of the reasons why that evidence might be lacking is that most livestock studies have not considered the grazing impact of sympatric European rabbits, the most widespread and abundant wild herbivore in southern Australia. Numerous studies have shown that rabbit grazing has a major impact on rangeland vegetation and can prevent regeneration at densities which may be too low to be thought important. Plant biodiversity gradients are readily discernible along gradients of rabbit density in livestock-free reserves. Rabbits are therefore likely to be a significant confounding factor when assessing livestock impacts, or possibly the primary cause of observed patterns of plant diversity. If so, attempts to preserve plant biodiversity by removing livestock are destined to fail in rabbit-grazed areas. Public funds for biodiversity conservation in the pastoral zone might be better spent on co-investment with pastoralists for rabbit control on conservatively stocked properties, rather than on restricting pastoral use of land in livestock-free, rabbit-infested reserves.

Can widespread generalist predators affect keystone prey? A case study with red foxes and European rabbits in their native range

AbstractWidespread generalist predators may affect declining keystone prey populations. However, this phenomenon is not well understood. In this paper, we assessed whether the abundance and population growth of European rabbits Oryctolagus cuniculus, a keystone prey species in Mediterranean Iberia, was related to the abundance and diet of red foxes, Vulpes vulpes, a widespread generalist predator. In a locality in central Spain, where rabbit population abundance declined, we estimated rabbit abundance during almost 3 years and determined fox abundance and diet during two concurrent years. We calculated a fox predation index (percentage of consumed rabbit biomass × fox abundance) to assess the importance of rabbits to foxes. We employed a multi–model approach to explain rabbit abundance and population growth. Foxes consumed between 60 and 99 % rabbit biomass in their diets, and this was independent of rabbit abundance. Periods of higher fox predation index coincided with lower rabbit density and vice versa. Two models best explained rabbit abundance and four rabbit population growth. They included the fox predation index and its interaction with rabbit abundance during the previous month. Altogether, fox predation, intraspecific density dependence, and their interaction partly explained rabbit population dynamics. We conclude that in order to propel the recovery of the rabbit in Iberia, it is essential to better understand the role of these factors in driving the abundance of the species.

Short communication. The role of rabbit density and the diversity of weeds in the development of cover crops in olive groves

Cover crops are an effective means to reduce soil erosion and to provide food and shelter for wildlife. However, in areas of intensive farming, which are characterised by the scarcity of weed communities, wild herbivores may focus their grazing on cover crops, which could make their implementation difficult. In this work, we test whether rabbit grazing can prevent the growth of herbaceous cover crops in olive groves in Southern Spain in addition to assessing the role of rabbit abundance and diversity of weeds in the development of cover crops. This question has been addressed by sowing Bromus rubens between the rows of five olive groves in Cordoba province (Spain). We then monitored the surface covered by B. rubens, along with both diversity of weed communities and rabbit abundance. Two rabbit exclusion areas were also placed in each olive grove in order to assess the impact of rabbits on the development of cover crops. Our results showed that the surface occupied by B. rubens was considerably higher in the rabbit exclusion areas (mean 56.8 ± 5.65 %) than in those areas in which they could feed (mean 35.6 ± 4.32 %). The coverage occupied by cover crops was higher in areas with lower rabbit density, although this relationship was modulated by the weed diversity index, since in areas with the same rabbit abundance the coverage was higher in those with a richer weed community. These findings suggest that high rabbit abundances can prevent the development of herbaceous cover crops in olive groves, particularly in areas in which alternative food resources (measured as weed diversity) are scarce.

Density‐dependent effects of a widespread invasive herbivore on tree survival and biomass during reforestation

Reforestation has been widely adopted as a solution to multiple global change issues. However, the role of herbivory by invasive species in the restoration of grassland to forest has received little attention. We conducted a field experiment to investigate the impacts of a widespread invasive mammalian herbivore, the European rabbit (Oryctolagus cuniculus), on trees planted in a landscape‐scale reforestation program in south‐eastern Australia. Three native tree species were planted inside and outside rabbit‐proof exclosures within 10 experimental units, and a random half of the units were subjected to intensive and sustained rabbit control for the remainder of the experiment. Quarterly survival of trees, and total aboveground biomass at the conclusion of the experiment, were estimated using hierarchical Bayesian models. Control substantially reduced rabbit densities on the five treatment units relative to the five non‐treatment units. Survival of trees planted outside exclosures was highest at lowest rabbit density and declined non‐linearly with increasing rabbit density for all three tree species, but even very low rabbit densities had strong negative effects on the survival of trees outside exclosures. There was a three‐way interaction between tree height, being outside an exclosure, and rabbit density. Smaller trees planted outside exclosures always had substantially lower overall survival than trees of the same height planted inside exclosures, and the magnitude of the difference increased with increasing rabbit density. Increasing rabbit densities reduced the overall survival of increasingly taller trees of all three species planted outside exclosures. The aboveground biomass of trees surviving outside exclosures was significantly greater in treatment units compared with non‐treatment units for all three species. The combined effects of differential survival and accumulation of aboveground biomass led to higher biomasses inside exclosures relative to outside exclosures just 21 months after planting. The aboveground biomass of trees planted outside exclosures declined with increasing rabbit density, and was effectively zero when rabbit densities exceeded 100 active warren entrances/ha. These results demonstrate that invasive herbivores can rapidly arrest the conversion of grassland to forest. Invasive herbivores such as the European rabbit may need to be completely excluded in order to maximize the benefits of reforestation.

The effect of aging on posterior intertransverse lumbar fusion: a New Zealand white rabbit model.

In vivo assessment of lumbar spinal fusion between a younger and older cohort of New Zealand white rabbits. Directly compare fusion within young and aged New Zealand white rabbits to establish an aged spinal fusion model translational research. Prior studies have utilized skeletally mature young rabbits (6-12 mo old) that may not be appropriate as an analog for studying the aging human spine. Ten aged (>36 mo old) and 10 young (12 mo old) New Zealand white rabbits underwent a single-level, bilateral, L5-6 posterolateral intertransverse fusion using autogenous iliac crest bone graft. The animals were killed at 6 weeks postoperatively, and the specimens were then evaluated with quantitative microcomputerized tomography and manual palpation by 6 orthopedic surgeons. The fusions were graded as either fused or not fused by each examiner. The spines were then embedded in poly(methyl methacrylate) and cut into 2-mm-thick sections for histologic analysis. A higher percentage of young rabbits were determined to be successfully fused through manual palpation testing compared with the aged rabbits. Micro-computed tomography (CT) analysis revealed a significantly greater fusion mass volume in the younger rabbits than in the older cohort. In addition, the fusion density of the younger rabbits was found to be significantly lower than that of the older rabbits when normalized to the bone density in the nonfused portion of the spine. Histologic analysis showed that the quality of the bone within the fusion mass was consistent between the young and old rabbits. A greater number of young animals had bilateral continuous bone graft compared with the aged animals. The aged (>36 mo) New Zealand white rabbit model appears to be a valid model to evaluate the effect of aging on lumbar fusion and has the potential to more accurately model conditions that are present in the older human spine.

Using multiple‐source occurrence data to identify patterns and drivers of decline in arid‐dwelling Australian marsupials

Many of the world's terrestrial mammal species are imperilled, but recent extinctions and declines have been most severe in Australia. In particular, arid‐dwelling marsupials in a critical weight range (35–5500 g) have declined dramatically following European settlement. In the absence of long‐term monitoring, documenting these declines or distribution shifts and their causes often relies on occurrence data from multiple sources. Using atlas records, we compared the distributions of all currently extant marsupials in the critical weight range in Australia's arid Northern Territory pre‐ and post‐1975. For taxa with evidence of range contraction, we evaluated alternative hypotheses to explain this contraction (i.e. competition, predation, productivity, climate) using several techniques to improve our confidence in the results. Despite a substantial increase in the number of mammal records across the study region post‐1975, the bilby Macrotis lagotis and desert form of the common brushtail possum Trichosurus vulpecula appear to have contracted in distribution by 25 and 40%, respectively. These changes in distribution were best explained by hypotheses of competition and climate‐change, respectively. Macrotis lagotis was more likely to occur on land without a history of cattle grazing and with low rabbit densities, while T. vulpecula has contracted to parts of its distribution that experience cooler maximum temperatures over the hottest months of the year. For five other taxa (including the vulnerable black‐footed rock‐wallaby Petrogale lateralis) we recorded increases in distribution post‐1975, probably reflecting increased survey effort rather than actual range expansion. We conclude that models using multiple‐source occurrence data can provide key insights into the patterns and drivers of contemporary species’ declines, and represent useful tools for conservation.

Seasonal habitat use by the European rabbit (Oryctolagus cuniculus) in a coastal dune system in SW Spain

We studied habitat use by the wild European rabbit (Oryctolagus cuniculus) in a coastal sand dune system in the south–western Iberian peninsula. Our goals were to define the use of this habitat by rabbits in relation to food and shelter availability between seasons. Rabbit density, food availability and refuge abundance were analysed using multiple regression analyses. We found that, independently of season, habitat selection was principally related to cover by the woody shrub Retama monosperma which rabbits use both as a food resource and as protection against predators. Although it is an invasive native plant, the benefits that R. monosperma provides.

Individual hunting behaviour and prey specialisation in the house cat Felis catus: Implications for conservation and management

Predators are often classed as prey specialists if they eat a narrow range of prey types, or as generalists if they hunt multiple prey types. Yet, individual predators often exhibit sex, size, age or personality-related differences in their diets that may alter the impacts of predation on different prey groups. In this study, we asked whether the house cat Felis catus shows individuality and specialisation in its hunting behaviour and discuss the implications of such specialisation for prey conservation and management. We first examined the prey types killed by cats using information obtained from cat owners, and then presented data on cat hunting efficiency on different prey types from direct observations. Finally, we quantified dietary shifts in cats when densities of their preferred prey varied. Twenty-six cats that returned 10 or more prey items to their owners showed marked differences in prey preferences (P<0.001), with eight cats specialising on small birds, five on lizards, four on black rats Rattus rattus, three on large birds, and six returning multiple prey types. Observations of 182 hunting attempts by 15 cats showed significantly high hunting efficiency (P<0.05) by four cats on rodents (83–100% of attacks on rodents were successful) and by one cat on rabbits Oryctolagus cuniculus (94% attack success), whereas 10 cats hunted two or three prey types with similar efficiency. At two field sites where rabbits were preferred cat-prey, the percentage of rabbit in the diet of cats showed quadratic relationships against rabbit density, with cats consuming rabbits when they were undetected in surveys. Our results suggest that cats can exhibit individual, or between-phenotype, variation in hunting behaviour, and will hunt specific prey types even when these prey become scarce. From a conservation perspective, these findings have important implications, particularly if cats preferentially select rare or threatened species at times when populations of these species are low. Determining whether prey specialisation exists within a given cat population should therefore be useful for assessing the likely risk of localised prey extinctions. If risks are high, conservation managers may need to use targeted measures to control the impacts of specialist individual cats by using specific baits or lures to attract them. We conclude that individuality in hunting behaviour and prey preference may contribute to the predatory efficiency of the house cat, and suggest that studies of the ontogeny and maintenance of specialist behaviours be priorities for future research.

High rabbit abundance proves detrimental to the population growth rate in European rabbit (Oryctolagus cuniculus L.) extensive breeding enclosures

The European rabbit (Oryctolagus cuniculus L.) is a key prey species in Mediterranean ecosystems that has declined in its natural ranges as a result of diseases and loss of habitat. This situation has led to the production of wild rabbits in enclosures in which they can acclimate and breed. The efficiency of these enclosures as extensive breeding systems is defined by their population growth rate (PGR). The aim of this study is to analyse the effect of rabbit abundance on the PGR. This has been done by creating general linear models to explain autumn and spring PGR with the use of rabbit abundance estimates, enclosure size, aerial predation and previous PGR as possible explanatory variables. Rabbit abundance and enclosure size negatively affected the autumn PGR, while only rabbit abundance affected the spring PGR in the best-fit models. It is suggested that maintaining rabbit densities at fewer than 30 rabbits per hectare might help to optimise the efficiency inside enclosures.

Role of prey and intraspecific density dependence on the population growth of an avian top predator

Exploring predator–prey systems in diverse ecosystems increases our knowledge about ecological processes. Predator population growth may be positive when conspecific density is low but predators also need areas with prey availability, associated with competition, which increases the risk of suffering losses but stabilises populations. We studied relationships between European rabbits Oryctolagus cuniculus (prey) and adult eagle owls Bubo bubo (predators) in south-western Europe. We assessed models explaining the predator population growth and stability. We estimated the abundance of rabbits and adult eagle owls during three years in eight localities of central-southern Spain. We explored models including rabbit and adult eagle owl abundance, accounting for yearly variations and including the locality as a random variable. We found that population growth of adult eagle owls was positive in situations with low conspecific abundance and tended to be negative but approaching equilibrium in situations of higher conspecific abundance. Population growth was also positively related to previous summer rabbit density when taking into account eagle owl conspecific abundance, possibly indicating that rabbits may support recruitment. Furthermore, abundance stability of adult eagle owls was positively related to previous winter–spring rabbit density, which could suggest predator population stabilisation through quick territory occupation in high-quality areas. These results exemplify the trade-off between prey availability and abundance of adult predators related to population growth and abundance stability in the eagle owl–rabbit system in south-western Europe. Despite rabbits have greatly declined during the last decades and eagle owls locally specialise on them, eagle owls currently have a favourable conservation status. As eagle owls are the only nocturnal raptor with such dependence on rabbits, this could point out that predators may overcome prey decreases in areas with favourable climate and prey in the absence of superior competitors with similar foraging mode.

Revisiting food‐based models of territoriality in solitary predators

Food availability is considered a major factor determining spacing behaviour in territorial species, especially for females. Theoretically, spatial overlap (considered the opposite of territoriality) and food availability are related in a nonlinear manner (hypothesized inverted-U function), with high overlap levels at the extremes of a food availability gradient and low overlap at intermediate levels of this gradient. Similar patterns are expected for encounter frequencies owing to its expected correlation with spatial overlap. However, these predictions have rarely been tested in highly structured social systems on a broad gradient of food availability, which implicitly requires experimental manipulation. We test these predictions in a solitary, territorial and trophic specialist, the Iberian lynx Lynx pardinus, taking advantage of a three-decade data set of spatial behaviour in different scenarios of food availability (i.e. rabbit density). In contrast with expectations, home range overlap among resident females was low (median overlap index = 0.08, range 0-0.57) and core area overlap was nearly nil (median overlap index = 0, range 0-0.22) throughout the entire gradient of prey availability. Furthermore, spatial associations between pairs of females were negligible regardless marked variation in prey availability. Therefore, we did not find support for a model of flexible lynx territoriality driven by food availability. Our results suggest that the exclusive use of space in the Iberian lynx was not related to food. Lack of influence of prey availability on lynx territoriality may be adaptive to cope with the consequences of frequent drought-induced periods of prey scarcity or other disturbance typically affecting wild rabbit populations in Mediterranean environments. Thus, lynx would adopt an obstinate strategy of territoriality that consists in defending exclusive areas across a broad range of resource availability ensuring an exclusive access to the minimum amount of prey necessary for survival and eventually reproduction even during periods of prey scarcity. However, we found signs that territoriality was influenced by lynx density in a nonlinear fashion. Our results suggest the occurrence of population regulation through territoriality in this species.

Predictive modelling to aid the regional-scale management of a vertebrate pest

Extensive resources are allocated to managing vertebrate pests, yet spatial understanding of pest threats, and how they respond to management, is limited at the regional scale where much decision-making is undertaken. We provide regional-scale spatial models and management guidance for European rabbits (Oryctolagus cuniculus) in a 260,791 km2 region in Australia by determining habitat suitability, habitat susceptibility and the effects of the primary rabbit management options (barrier fence, shooting and baiting and warren ripping) or changing predation or disease control levels. A participatory modelling approach was used to develop a Bayesian network which captured the main drivers of suitability and spread, which in turn was linked spatially to develop high resolution risk maps. Policy-makers, rabbit managers and technical experts were responsible for defining the questions the model needed to address, and for subsequently developing and parameterising the model. Habitat suitability was determined by conditions required for warren-building and by above-ground requirements, such as food and harbour, and habitat susceptibility by the distance from current distributions, habitat suitability, and the costs of traversing habitats of different quality. At least one-third of the region had a high probability of being highly suitable (support high rabbit densities), with the model supported by validation. Habitat susceptibility was largely restricted by the current known rabbit distribution. Warren ripping was the most effective control option as warrens were considered essential for rabbit persistence. The anticipated increase in disease resistance was predicted to increase the probability of moderately suitable habitat becoming highly suitable, but not increase the at-risk area. We demonstrate that it is possible to build spatial models to guide regional-level management of vertebrate pests which use the best available knowledge and capture fine spatial-scale processes.

Density and habitat use of sympatric Brown hares and European rabbits in a Mediterranean farmland area of Tuscany (Central Italy)

Use of habitat by sympatric Brown hare (Lepus europaeus) and wild European rabbit (Oryctolagus cuniculus) was investigated in a farmland area of western Tuscany from 1999 to 2011. We used spotlight counts in winter and indirect surveys on faecal pellet counts in spring–summer. The density of Brown hare increased during the study period, whereas the European rabbit population crashed in 2010 after a European Rabbit Haemorrhagic Disease (RHD) outbreak.The results of the use of habitat type differed between the observations obtained during the spotlight census and the observations obtained from the indirect surveys carried out using faecal pellet counts.The two lagomorph populations showed a great habitat overlap; however, European rabbits seem to live at a shorter distance from permanent cover such as hedgerows and woods and seem to prefer uncultivated fields and permanent crops such as olive tree groves that offer more protection from avian predators. Brown hares seem to prefer more open habitat such as arable crops and this resulted in them being less selective than European rabbits. The differences found in habitat use have probably enabled the two species to coexist for many decades and can be used to manage these lagomorphs.

A rapid survey method for estimating population density of European rabbits living in native vegetation

European rabbits are severe environmental pests in Australia but reporting of density-damage relationships has been hindered by a lack of simple methods to estimate the density of rabbit populations in native vegetation. A methodology for quantifying rabbit densities suitable for use in sparse populations of rabbits in conjunction with surveys of the condition of native vegetation is proposed. Dung pellets were counted in 11 629 regularly-spaced quadrats of 0.1 m2 in semiarid, coastal and cool-temperate areas of southern Australia. Mean pellet counts in latrines and the relationship between dung counts outside of latrines and the proportion of quadrats falling on latrines were quantified. This allowed density of dung pellets to be estimated by using a correction factor for latrines instead of attempting to count all pellets within quadrats that included parts of latrines. Rabbit density was calculated from pellet density based on mean pellet size, pellet breakdown rate and estimates of rabbits’ dry matter intake and digestive efficiency. Results were validated against estimates of rabbit density from long-term studies using a combination of spotlight transect counts and burrow entrance counts. The proposed methodology allows estimates of rabbit density in native vegetation to be obtained from just a few hours work and can be used in conjunction with surveys of the condition of native vegetation to quantify rabbit impacts. This methodology is seen as particularly useful in providing a tool to allow rabbit densities to be estimated and then compared with the thresholds, determined separately, at which damage occurs for given ecosystems.