Rabbit Abundance Research Articles

Effectiveness of habitat management in the recovery of low-density populations of wild rabbit

Understanding the relationship between spatial patterns of landscape attributes and population presence and abundance is essential for understanding population processes as well as supporting management and conservation strategies. This study evaluates the influence of three factors: environment, habitat management, and season on the presence and abundance of the wild rabbit (Oryctolagus cuniculus), an important prey species for Mediterranean endangered predator species. To address this issue, we estimated wild rabbit presence and abundance by latrine counting in transects located in 45 plots within a 250 × 250 m grid from June 2007 until June 2009 in a 1,200 ha hunting area in southern Portugal. We then analyzed how wild rabbit presence and abundance correlate with the aforementioned factors. Our results showed that the main variable influencing wild rabbit presence and abundance was the distance to the artificial warrens. North and northeast slope directions were negatively related to wild rabbit presence. Conversely, rabbit presence was positively correlated with short distances to ecotone, artificial warrens, and spring. Regarding rabbit abundance, in addition to artificial warrens, soft soils, bushes, and season also had a positive effect. We found that environmental variables, management practices, and season each affect wild rabbit presence and abundance differently at a home range scale in low-density population. Thus, our major recommendations are reducing the distance to artificial warrens and ecotone, ideally to less than 100 m, and promoting habitat quality improvement on slopes with plenty of sun exposure.

Long-term spatio-temporal expansion of the native-invasive Retama monosperma on coastal dunes: Importance of land-use and natural dispersal vectors

Expansion of invasive species inducing sands stabilization is becoming an important ecological problem in coastal dunes in some parts of the world. Retama monosperma, an endemic to coasts of SE Spain and NE of Morocco, late-colonizing shrub occurring in sandy coastal areas, was planted along the coast of SW Spain during the 20th century to stabilize dunes. In recent decades, the species has spread rapidly, becoming invasive, and sometimes incurring notable changes in its environment and plant community. The expansion patterns of R. monosperma from 1956 to 2001 were described and quantified at the landscape scale within a protected dune system, using GIS. The differential effects on expansion patterns of the main factor controlling the population spread, grazing by domestic livestock and the abundance of wild rabbits, were analyzed comparatively. R. monosperma displays an exponential, invasive-type expansion trend, presenting a mean annual coverage increase of 15% and a mean lateral spread rate of 65.5myr−1 from the original population nucleus to the Western and Eastern ends of the study area. The dispersal activity primarily of rabbits and the absence of competing woody species contribute to this rapid expansion. The highest local increases in plant coverage could be related to increased rabbit abundance and to the improved germination rates of seeds which have passed through the rabbit gut. In contrast, areas highly grazed by livestock present the lowest increases, and an open-type plant community is maintained there for a longer time.

The short-term effect of total predation exclusion on wild rabbit abundance in restocking plots

About half a million rabbits are translocated in southwestern Europe every year for conservation and hunting purposes. However, the success of traditional rabbit restocking is generally extremely low, and this has been attributed to short-term predation by mammalian carnivores. Hence, recent recovery programs have tackled the problem of terrestrial predators with the use of exclusion fences, but no additional measures have been employed to avoid aerial predation. In this study, we have therefore conducted a field experiment to test the short-term effect of total predation exclusion in rabbit restocking enclosures, comparing rabbit abundance in plots which are only accessible to raptors (top-open plots) and plots which are accessible to neither carnivores nor raptors (top-closed plots). The results showed that the top-closed plots had higher rabbit abundance in the short term, and the highest difference in rabbit abundance between the two kinds of fences was attained in the first 2 weeks. We therefore conclude that the top-closed plots were an effective tool to increase rabbit abundance during the first weeks after release through the exclusion of raptor predation.

Key factors determining the seasonal population growth rate of European wild rabbits and their implications for management

Recently, the European rabbit (Oryctolagus cuniculus) has received contrasting considerations due to its multidimensional role in the Mediterranean ecosystems. Within this framework, knowledge of factors determining its population size may have important consequences for designing an effective management plan. In this paper, we quantified the combined influence of the major demographic and mechanistic factors on seasonal population fluctuation of European rabbits on Lemnos Island (Greece), during 2007–2009. We developed a hypothetical model taking into account direct (productivity, predation, hunting pressure, food shortage, habitat treatment) and indirect factors (soil moisture, adverse weather conditions) using structural equation modeling. We tested for their influence on the seasonal population growth rate (spgr) as determined by line transects to estimate rabbit abundance. The productivity induced higher pgr. Food shortage, which is affected by low soil moisture during the late summer and early autumn, is demonstrated to be the most important negative factor followed by the hunting pressure and predation. Demographic and mechanistic factors highlighted in this analysis could be used either for conservation or for controlling populations of the species.

COCCIDIAN AND NEMATODE INFECTIONS INFLUENCE PREVALENCE OF ANTIBODY TO MYXOMA AND RABBIT HEMORRHAGIC DISEASE VIRUSES IN EUROPEAN RABBITS

The interaction among several parasites in European rabbits (Oryctolagus cuniculus) is crucial to host fitness and to the epidemiology of myxomatosis and rabbit hemorrhagic disease. These diseases have caused significant reductions in rabbit populations on the Iberian Peninsula. Most studies have focused on the epidemiology and pathogenesis of these viruses individually, and little is known about interactions between these viruses and other parasites. Taking advantage of an experimental restocking program in Spain, the effects of coccidian and nematode infections on the probability of having detectable antibody to myxoma and rabbit hemorrhagic disease viruses were tested in European wild rabbits. For 14 mo, we monitored rabbit abundance and parasite loads (coccidia and nematodes) in three reintroduced rabbit populations. While coccidian and nematode loads explained seasonal antibody prevalences to myxoma virus, the pattern was less clear for rabbit hemorrhagic disease. Contrary to expectations, prevalence of antibody to myxoma virus was inversely proportional to coccidian load, while nematode load seemed to play a minor role. These results have implications for viral disease epidemiology and for disease management intended to increase rabbit populations in areas where they are important for ecosystem conservation.

Motorway verges: Paradise for prey species? A case study with the European rabbit

Roads have many effects on the mammal populations of their surroundings. Prey species are thought to establish dense populations in road verges due to a predation release effect, which arise as a side-effect of roadside avoidance by predators and/or predator roadkill. A species that has been suggested to benefit from predation release and attain high densities near roads is the European rabbit, a keystone species in Mediterranean ecosystems. We monitored rabbit relative abundance at three distances from a motorway (50, 450 and 850m) during a 6 month period, as well as hunting and predator pressures, in a suitable area for rabbits. The lowest rabbit abundance was found next to the motorway (6.76±8.87 pellets/m2 per month) and the highest abundance at an intermediate distance (17.65±23.11 pellets/m2 per month). Hunting and carnivore pressures were highest at the sampling transect located farthest from the infrastructure. Thus, variability in rabbit abundance did not match the predation release effect found close to the motorway, and some sort of road avoidance or other process must underlie the observed abundance pattern. We advocate for a formal measurement of prey populations response to roads prior to any generalization as, in the case of rabbit, the response to roads and the potential cascading effects on other species may depend on landscape characteristics.

Monitoring population size of mammals using a spotlight-count-based abundance index: How to relate the number of counts to the precision?

Abundance indices are widely used to study changes in population size in wildlife management. However, a truly appropriate measure of precision is often lacking in such studies. Statistically, the two crucial issues regarding the use of an abundance index are sampling and observability, which lead one to consider two kinds of errors, namely sampling and observation errors. The purpose of this methodological paper is to relate the number of counts to the precision of an abundance index by introducing the Hansen–Hurwitz–Bershad model which takes into account both sampling and observation errors. We illustrate this statistical approach in the case of a European rabbit (Oryctolagus cuniculus) abundance index based on spotlight counts, for two fixed spatial sampling units located in different ecological contexts. We show (i) that the usual sampling variance estimator is a downward-biased estimator of the total variance of the abundance index, (ii) that the bias of the usual variance estimator does not decrease when increasing the sampling size, (iii) that correlated observation errors may have a dramatic impact on the total variance, especially when the sampling size increases. The acknowledgement that the (pure) sampling variance underestimates the total variance because of observation errors is a statistical result that is neither widely known nor appreciated by most wildlife ecologists. The magnitude of this underestimation may be important and, therefore, observation errors cannot be always considered as a priori negligible in assessing the precision of a count-based abundance index.

European rabbit survival and recruitment are linked to epidemiological and environmental conditions in their exotic range

AbstractThe European rabbit, Oryctolagus cuniculus, is threatened within its native range, yet it is a highly successful colonizing pest species across its worldwide introduced range, causing large economic losses and widespread environmental degradation. To date, there has been no long‐term empirical evidence documenting the relative roles of climatic, epidemiological and biological factors in limiting life‐history determinants of rabbit range and abundance. Using 12 years of capture–mark–recapture data from their exotic range in Australia, we constructed candidate Cormack–Jolly–Seber models to test the influence of environmental, competition and disease conditions on rabbit survival and recruitment. Our results show that: (i) population‐level disease infection rate has the largest overall impact on rabbit survival, explaining 80% of variance in survival rates; (ii) environmental as well as epidemiological conditions constrain rabbit survival, especially for younger animals; (iii) temporal variation in rabbit kitten recruitment patterns are best described by a combination of climate, competition and disease settings (accounting for 68% of variance), while temperature alone has a strong negative influence on kitten recruitment; and (iv) recruitment responds positively to rabbit haemorrhagic disease, but negatively to myxomatosis – the former, probably being mediated through a disease driven effect on intraspecific competition for food. A strengthened understanding of climate change impacts on rabbit range and abundance can be achieved by accounting explicitly for potential synergisms between disease dynamics and climate. In this analysis, we provide the first step towards such an attempt for this important mammal species. Integrated approaches of this kind are essential for future forecasts of rabbit range and abundance, offsetting the conservation threat faced by O. cuniculus in its native range, and achieving effective management in exotic habitats.

Can we explain regional abundance and road‐kill patterns with variables derived from local‐scale road‐kill models? Evaluating transferability with the European polecat

AbstractAim We evaluated the transferability of variables previously found to have a significant effect on European polecat Mustela putorius road‐kills at a local scale (i.e. 50 m around location points) when we extrapolate them to a large scale [Universal Transverse Mercator (UTM) 100 km2] in a neighbouring area.Location Andalusia, south Spain. We carried out our study in 821 of the 985 UTM 100 km2 cells included in this region.Methods The units of the different variables were adapted to the new scale. We used data from the Spanish Atlas survey to obtain the abundance of the different species and GIS data for the rest of the variables. We controlled the spatial autocorrelation by incorporating spatial filters obtained with Spatial Eigenvector Mapping into multiple regression analyses. We used AIC criteria and the best subset procedure to investigate the relationship between the selected variables and species abundance, and road‐kill occurrence.Results The best subset procedure provided two models that explained 40% of variation in polecat abundance and eleven models that explained around 25% of variation in road‐kills. The main explanatory factor for polecat abundance was the abundance of other carnivores, whereas polecat abundance was the main factor for road‐kills. In both cases, rabbit abundance was the second most important explanatory variable.Main Conclusions Our findings highlight the possibility of partially explaining the abundance and road‐kill patterns at a large scale based on significant variables from local‐scale models. Mitigation measures to reduce polecat fatalities should combine actions at different scales. Routes that cross carnivore hotspots, including those of polecats, and areas with important populations of rabbits, should be avoided during road planning. When these routes are unavoidable, local‐scale mitigation measures must be implemented.

Feeding the Foxes: An Experimental Study to Assess Their Taphonomic Signature on Leporid Remains

ABSTRACTThe red fox (Vulpes vulpes) is a generalist predator, but in areas where the abundance of rabbits is high, they constitute one of the most common prey species. Taphonomic studies on leporid remains consumed by this terrestrial carnivore are scarce, and its role as an agent responsible for bone accumulations in the fossil record is not fully understood. With the aim of contributing new data to this subject, an experimental study was carried out with four red foxes kept in captivity. They were fed with complete rabbit carcasses. Scats and non‐ingested remains were recovered in order to analyse anatomical representation, breakage and digestion patterns. Results were compared with another sample derived exclusively from wild red foxes' scats. Variability occurs among the three samples, suggesting that the identification of the taphonomic signature of this predator on archaeological assemblages of leporid remains is not a straightforward matter. Copyright © 2011 John Wiley & Sons, Ltd.

Predation determines the outcome of 10 reintroduction attempts in arid South Australia

Ten reintroduction attempts were conducted in and around the Arid Recovery Reserve in northern South Australia between 1998 and 2008. Five locally-extinct mammal species and one reptile species were reintroduced into a fenced Reserve where cats, foxes and rabbits were excluded. Reintroductions of the nationally threatened greater stick-nest rat, burrowing bettong, greater bilby and western barred bandicoot were all considered successful based on short and medium-term success criteria. These criteria included continued survival after 8years, increased distribution across the large Reserve and, most importantly, recovery after a drought event. The trial reintroductions of the numbat and woma python into the Reserve were unsuccessful due to predation by native avian and reptilian predators respectively. Outside the Reserve, where cats and foxes were present but controlled through poison baiting, reintroduction attempts of the greater bilby and burrowing bettong were unsuccessful. High mortality was attributed to cat and fox predation with dingoes also contributing to post-release mortality in bettongs. However, a reintroduction of burrowing bettongs into a fenced area with low rabbit and cat abundance has, to-date, met short-term and medium-term success criteria. Results suggest that the absence or severe restriction of exotic mammalian predators was the critical factor responsible for the success of the mammal reintroductions. Determining thresholds of predator activity below which successful reintroduction of threatened species can occur, are needed to improve the science of reintroduction biology in Australia.

Assessing predictors of pellet persistence in European rabbits Oryctolagus cuniculus: towards reliable population estimates from pellet counts

AbstractThe European rabbit Oryctolagus cuniculus is a key species in Mediterranean ecosystems of the Iberian Peninsula, and reliable methods for monitoring its abundance are urgently required. Although clearance plot pellet counts may be useful in monitoring rabbit populations, such counts are potentially affected by variation in the persistence of rabbit pellets. The aim of our study was to assess persistence of rabbit pellets in the Iberian Peninsula for reliable estimates of rabbit abundance from clearance plot counts. We carried out the experiment from July 2006 to November 2007 at seven localities in central southern Spain. Marked fresh pellets were monthly placed at experimental plots, and their persistence was monitored monthly. Persistence was estimated from the proportion of marked pellets remaining between consecutive counts. Independent variables in analysis included slope steepness, vegetation, rabbit and ungulate activity, meteorology and temporal variables. Persistence significantly varied among localities and seasons and with their interaction. The final model showed that pellet persistence was best explained by total rainfall between counts, and also included the time between visits and slope steepness and the interactions rainfall∗time between visits and rainfall∗slope. Our results suggest that estimating pellet persistence for each locality and season is necessary to make estimates obtained from different localities and months comparable. In the Mediterranean region, early summer at the start of the dry season would be the recommended time for yearly rabbit monitoring based on any pellet‐count index, since reduced rainfall favours pellet persistence. Sampling protocols must standardise the number of days between counts, and plots must be established in areas with gentle slope to maximise pellet persistence between counts.

Widespread exposure to Sarcoptes scabiei in wild European rabbits (Oryctolagus cuniculus) in Spain

Sarcoptic mange was recently described in the wild European rabbit (Oryctolagus cuniculus) in north-eastern Mediterranean Spain, the first such infection reported in this species anywhere in the world. This finding has created concern in conservationists and game managers given that an outbreak of mange after a translocation would have catastrophic consequences for naïve rabbit populations in other parts of Spain. A retrospective serosurvey using an ‘in house’ ELISA test based on the use of a recombinant antigen aimed at determining the rates of contact with Sarcoptes scabiei was carried out on sera from 966 rabbits collected between 1993 and 2010 in Spain. Antibodies were found in 13% of wild rabbits in 60% of the 53 areas surveyed, as well as in 16 of the 17 Spanish provinces and islands studied. Seropositive rabbits were found amongst the oldest samples analyzed and in all studied years. Antibodies were also detected in 36% of rabbits from the protected island of Dragonera, where rabbits have probably not been released since the 1970s. On Mallorca, where 89 rabbits were inspected for both lesions and antibodies, the prevalence of lesions (5.6%) was much lower than the seroprevalence (22.5%), indicating that rabbits often survive infection or that ELISA detects infected rabbits before they develop visible lesions. Seroprevalence was higher in areas with medium levels of rabbit abundance, no restocking and high rainfall. The results show that mange is widespread in rabbits and that the mite is not a recent introduction. Thus, sarcoptic mange could be considered as an enzootic disease in the wild rabbit and so prophylactic measures implemented during rabbit translocations are to be encouraged to avoid local outbreaks in naïve populations.

Development of an index of abundance for pygmy rabbit populations

ABSTRACT The pygmy rabbit (Brachylagus idahoensis) is a cryptic, burrowing lagomorph of conservation concern for which an efficient method to monitor populations is needed for conservation planning. We developed an index of abundance based on density of active burrow systems at 7 sites (57.2–118.5 ha) in east central Idaho. We conducted censuses of burrow systems and used mark-resight surveys of 80 radio-collared individuals to estimate density of rabbits. At 5 sites, we also used a second method to estimate rabbit numbers based on presence of tracks in snow around burrow systems. We evaluated patterns of burrow use by individuals and examined the relationship between vegetation structure and density of rabbits. Density of active burrow systems varied from 0.19 to 3.46 per ha, and density of rabbits ranged from 0.02 to 0.46 per ha. Number of burrow systems used by individuals increased with density of available burrows, which supported a nonlinear relationship between abundance of burrows and rabbits. Pop...

Towards a standardized index of European rabbit abundance in Iberian Mediterranean habitats

European rabbits Oryctolagus cuniculus are a keystone species in Iberian Mediterranean ecosystems. However, the reliability of methods for estimating rabbit abundance, particularly when at low numbers, is not well understood. Further, better standardization of these methodologies would allow abundance estimates to be more reliably compared between areas and periods. Consequently, we compared several frequently used methods of estimating rabbit abundance and assessed their advantages and disadvantages. During the summers of 2008 and 2009, in 11 localities of central-southern Spain we undertook (a) driving transect counts of rabbits, either at dusk or at night, (b) linear transects on foot recording rabbit signs, (c) cleared-plot pellet counts at permanent plots, and (d) standing crop counts, both with and without habitat stratification. Density estimated at night from driving transects using the Distance Sampling method (the reference method against which all other indices were compared) varied from 0 to 2.69 rabbits ha−1. Most pellet-count indices were significantly related to the reference method. In particular, cleared-plot pellet counts in permanent plots corrected for pellet persistence showed the best correlation with the reference method. In contrast, latrine counts were not related to the reference method index, and we recommend against their use. A standard methodology based on cleared-plot pellets counts could be used to monitor rabbit abundance on a large scale.

Fragmentation of sagebrush communities: does an increase in habitat edge impact pygmy rabbits?

AbstractSagebrush (Artemisia spp.) communities are ecologically critical; however, these areas currently face severe threats from alteration and reduction. Pygmy rabbits Brachylagus idahoensis are sagebrush specialists that occupy the intermountain region of the USA. Little is known concerning how fragmentation of sagebrush and an increase in habitat edge may impact pygmy rabbits. From 2004 to 2009 in Utah, USA, we tested hypotheses concerning the influences of habitat edge on pygmy rabbits. We quantified the number of active pygmy rabbit burrows in relation to distance from habitat edge. At differing distances from habitat edge, we also deployed remote cameras at burrows and counted fecal pellets to document potential increases in the number of terrestrial predators and competitors. We classified activity of 528 burrows (284 active and 244 inactive). The proportion of active burrows was lower within 100 m of habitat edge (r2=0.502, P=0.02) compared with burrows located in control areas (>100 m from habitat edge). Photographs of pygmy rabbits decreased at burrows closer to habitat edge (P<0.01). Photographs of predators increased near habitat edge, but was marginally insignificant (P=0.07), and photographs of potential competitors [cottontail (Sylvilagus spp.), P<0.01; jackrabbit Lepus californicus, P<0.01] increased near habitat edge. Fecal pellet plots supported these patterns. Our results indicated that the proportion of active burrows and the relative abundance of pygmy rabbits were reduced near habitat edge. This reduction was associated with an increase in terrestrial predators and competitors near habitat edge. Consideration should be given to the influence of habitat edge on pygmy rabbits in order to conserve and manage this unique species.

The feeding ecology of Bonelli’s eagle (Aquila fasciata) floaters in southern Spain: implications for conservation

Although many studies have investigated the feeding habits of Palaearctic raptors, few have analysed non-breeding populations during dispersal. Bonelli’s eagle (Aquila fasciata), a threatened species in Western Europe, has a relatively long and critical dispersal period. We studied feeding habits, prey selection, and the influence of prey density on floater abundance in this species during its dispersal period in southern Spain. Differences were found between the diet of floaters and that of the closest breeding populations. Diet diversity was rather low for floaters, with European wild rabbits (Oryctolagus cuniculus) being the main prey and the only prey positively selected. Moreover, the number of floater Bonelli’s eagles observed in the dispersal areas was positively associated with rabbit abundance. Other prey included red-legged partridges (Alectoris rufa) and pigeons (Columba sp.). We propose measures to match suitable prey availability for floater eagles in settlement areas and the use of such areas as human hunting fields.

The presence of a “competitor pit effect” compromises wild rabbit (Orcytolagus cuniculus) conservation

Abstract Wild rabbit (Oryctolagus cuniculus) populations have suffered a dramatic reduction over the last 30 years in Spain. Rabbit decline has been recurrently associated with several epizootics and habitat changes. The role of interspecific competition has been usually neglected. This study analyzes the effects of habitat suitability and wild boar (Sus scrofa) occurrence, a hypothetical predator and competitor species, on a small and isolated population of rabbits. To test this effect we used a GLM with the abundance of rabbits as response variable and wild boar occurrence as predictor. To avoid habitat confounding effects we included vegetation structure variables and elevation summarized in PCA factors. Rabbits showed a very restricted and aggregated distribution and a very low abundance across the study area. In contrast, wild boar was present in all sampled plots but one and showed moderatehigh abundance. The three best models included both wild boar occurrence and principal component factor 2. Rabbits were located in opened Mediterranean areas where trees were small and scarce, rock cover was low and wild boar occurrence was also low. Nowadays wild boar populations are not directly controlled in private lands and its hunting is forbidden in National Parks in Spain. Waiting for further research to evaluate the threshold of rabbit densities below which competitors and/or predators may prevent the recovery of rabbit populations, control of wild boars may be useful as a short-term strategy to recover small rabbit populations whenever it is linked to habitat improvements.

Rabbit Abundance Relative to Rainfall and Plant Production in Northern Chihuahuan Desert Grassland and Shrubland Habitats

ABSTRACT. Rabbit abundance patterns in the North American Southwest are poorly known, particularly relative to the potentially important influences of rainfall and plant production. We conducted a 10-year study on the comparative densities of black-tailed jackrabbits (Lepus californicus) and desert cottontail rabbits (Sylvilagus audubonii) in relation to annual rainfall and plant production in both black grama (Bouteloua eriopoda) grassland and creosotebush (Larrea tridentata) shrubland habitats in the northern Chihuahuan Desert. We found that both species of rabbits were more abundant in black grama grassland than in creosotebush shrubland and that plant production was positively correlated with rainfall at both habitats. However, rabbit densities were not positively correlated with rainfall or plant production in either habitat. In fact, both species of rabbits exhibited gradual, multiyear changes in abundance rather than the patterns of high annual variation observed in desert rodent communities. Our f...

Population estimation and monitoring of an endangered lagomorph

We conducted the most intensive estimate of the endangered Lower Keys marsh rabbit (Sylvilagus palustris hefneri) metapopulation to date using pellet surveys and capture–recapture methodology. We livetrapped 83 rabbits, evaluated 5 closed population models, and selected the model that best represented the data. We considered the variation in behavioral response model the best model and correlated (r2 = 0.913) its patch population estimates to patch pellet densities. From the prediction equation, we generated a range-wide metapopulation estimate of 317 rabbits, a western clade population of 257 rabbits, an eastern clade population of 25 rabbits, and translocated marsh rabbit populations of 35 and zero on Little Pine and Water keys, respectively. A subset of patches whose marsh rabbit subpopulations were last estimated in 1993 exhibited a 46% decline in abundance over 15 yr. Due to the low estimate of the eastern clade population, special effort should be initiated to avoid loss of genetic diversity. The prediction equation suffers from limited data at high pellet densities, patches with ≥5 pellets/m2. Future studies should investigate if the slope of the regression is indeed near 1 by sampling patches across the range of pellet densities, especially those with ≥5 pellets/m2. The equation provides managers a quick, efficient, and noninvasive method to estimate marsh rabbit abundance from pellet counts but the confidence of predicted rabbit densities from high pellet density patches is low. © 2011 The Wildlife Society