Improving predictions of the location and use of warrens in sensitive rabbit populations

The location and use of warrens is a key factor in the population dynamics of the European rabbit Oryctolagus cuniculus L., which can influence stability and persistence in the long term. Within the species' original distribution range, its numbers have declined sharply in recent decades, which is a serious problem for the conservation of Mediterranean ecosystems. Artificial warrens are commonly used to bolster rabbit populations and the characterization of natural warrens in those areas might improve their efficiency. In this study, we use binomial generalized linear models to identify the factors associated with the location and use of warrens in a low-density area and we evaluate the effect of including the spatial structure of the data in the model. In addition, we generate a map that predicts the most suitable areas for artificial warrens. Contrary to what was expected, habitat variables are only secondary factors, and the location and use of warrens is influenced mainly by spatial factors, such as proximity to nearby warrens. Furthermore, the aggregated spatial pattern of warrens suggests that, at the local scale, for example, the hunting estate, intra-specific interactions might be playing a primary role in these low-density populations. To identify the most suitable sites for artificial warrens and, thereby, improve the efficiency of artificial warren building for conservation purposes, information about spatial structures should be included in models predicting natural warrens of European rabbits.     

When more is less: the negative effect of European rabbit release upon local warren occupancy

European rabbit translocation is an extended practice in Spain, France, and Portugal, for both conservation and hunting purposes. Some of these translocations are carried out with the aim of reinforcing existing rabbit populations. In these cases, some of the new rabbits are released into warrens already occupied by resident conspecifics. This could have a negative impact upon both the released and the resident individuals owing to the “dear enemy” effect and the territoriality of the resident rabbits. In this study, we evaluated the effect of rabbit release into occupied warrens, in small areas populated by low-density resident rabbit populations. We observed negative effects at two different levels: the number of active entrances per recipient warren and the number of active warrens per reinforced plot, in addition to a general lack of increase in rabbit abundance in the area and, therefore, the failure of the reinforcement actions. Our results strongly suggest that the release of European rabbits into warrens occupied by resident rabbits is contraindicated if the objective is to recover rabbit populations in the area.     

Formation of nutrient‐poor soil patches in a semi‐arid woodland by the European rabbit (Oryctolagus cuniculus L.)

Abstract European rabbits (Oryctolagus cuniculus L.) occur over large areas of eastern Australia, where they disturb significant quantities of soil while constructing warrens. Although the effects of rabbits on vegetation are generally well understood, little is known about their effects on soil physical or chemical properties. We studied the effect of rabbit warrens on soil chemistry in a semi‐arid woodland supporting a high density of rabbit warrens. Within one large warren, we examined nutrient concentrations within three microsites (mound, inter‐mound and an intermediate disturbed area) representing a gradient of increasing rabbit disturbance, and supported this with a study of soil nutrients with depth within 1‐m‐deep trenches through five warrens. Landscape‐level changes in surface chemistry were also examined at an additional 23 warrens. At both patch and landscape scales, pH, electrical conductivity, soluble and exchangeable Ca²⁺ and K⁺, and total Al and Ca generally increased with increasing rabbit disturbance, while total C and S (LECO), total P and S (ICP), and soluble Na⁺ declined, and total N remained unchanged. Although chemical changes with depth were generally ill defined, surface soils tended to be more similar in their composition than deeper soils. Overall, our results reinforced the view that rabbits have a negative effect on surface soils in semi‐arid woodlands, and suggested that restoration of the original woodland vegetation may be hampered by changes in soil biogeochemistry associated with the warrens.     

Short-Term Vegetation and Soil Responses to Mechanical Destruction of Rabbit (Oryctolagus cuniculus L.) Warrens in an Australian Box Woodland

We studied the impact of disturbance by rabbits on plants and soils along a gradient out from the center of ripped rabbit warrens in an Australian semiarid woodland. Five years after the warrens were ripped, the impact of rabbits was still apparent. The cover of bare soil declined, and the cryptogam cover increased with increasing distance from the warren mound. However, litter cover, plant cover, and plant diversity remained unchanged with increasing distance from the mounds. Differences in plant composition were apparent with increasing distance from the mounds, with three species, Schismus barbatus, Salsola kali var. kali, and Chenopodium melanocarpum dominating the mounds, whereas the perennial grass Austrostipa scabra dominated the nonwarren control surfaces. Two species, Crassula sieberana and S. barbatus, dominated the active soil seed bank on ripped warrens. The mounds had the lowest number of species in the soil seed bank, whereas the warren edge microsite had the greatest. Ripped and unripped warrens differed substantially in their complement of species, and ripped warrens contained an order of magnitude fewer active warren entrances compared with unripped warrens. Ripped warrens also had significantly more plant cover than unripped warrens. Taken together, our results reinforce the view that rabbits have a destructive effect on surface soils and vegetation in semiarid woodlands and suggest that restoration of the original woodland vegetation after warren ripping is likely to be a slow and ongoing process.     

Provision of artificial warrens as a means to enhance native wild rabbit populations: what type of warren and where should they be sited?

In Spain, wild rabbits are essential for some highly endangered species, and, therefore, many actions have been undertaken to increase their populations. In the present study, artificial warrens are provided as a means to increase shelter for native wild rabbit populations in a given area. We evaluate the use of three types of warrens by rabbits and the effect on that use of five habitat characteristics at two spatial scales (500 × 500-m grids and 25-m plots). To evaluate that use, we identified pre-established signs at the entrances to each warren, and based on this, we calculated occupancy rate and activity. Our results indicate that rabbit abundance within a grid is the only variable which simultaneously explains both the greater occupancy and the higher activity in the artificial warrens located in that grid. Some 73.2% of the grids showed signs of rabbit use at the time of the evaluation. However, the pre-existing rabbit populations within the grids were not quantified and, hence, we cannot state that the warrens contributed to an increase in the rabbit abundance. Regarding the habitat, our results reveal that warrens should be situated in grids with food coverage of less than 50%, while the use of each individual refuge is greater where food availability in the immediate surroundings is at least 20% and shelter at least 50%. The tube warrens showed significantly greater rabbit use than the other types while there was little difference between the stone and pallet warrens in terms of use.     

Seasonal cycles of plasma testosterone and cortisol in the wild rabbit (Oryctolagus cuniculus algirus Loche) of Zembra Island, studied in its natural biotope and in captivity

Annual variations in plasma testosterone and cortisol levels were determined in male wild rabbits caught monthly in their natural biotope (Zembra island). For comparison, a group of warrens was hold in semi-captivity close to Tunis. In both conditions plasma testosterone concentrations were low from January to September and peak values were observed in October. Captive warrens exhibited a clear cut annual rhythm in plasma cortisol levels also and ether stress resulted in a very large increase of cortisolemia. In rabbits caught in ther habitat however, cortisol concentrations were always extremely high throughout the year, probably due to stressing conditions. Interestingly, wild rabbits of Zembra island appear to subsist from a very remote past without any contact with other strains. As to Zembra, it is a hardly get-at-able, uninhabited island which is a part of a strictly protected natural reserve and constitutes a fairly useful and valuable ecosystem.     

Responses of naïve and experienced European rabbits to predator odour

The response of prey species to predator scent has been investigated in many mammalian species; however, there is little information about the responses of European wild rabbits at the population level. Therefore, we conducted a simple experiment to investigate the behavioural response of a rabbit population to native predator cues in the wild. We compared the response to the scent of a predator (red fox) in a wild rabbit population bred in semi-natural conditions and naïve to terrestrial predators with the response of a population in a similar environment where terrestrial predators were present. The response to predators was based on rabbit abundance, inferred from pellet counts and measured by the defecation rate per day (DRD). Our results indicate that rabbits responded to the odour of fox faeces in the treatment warrens, resulting in a lower DRD. The main anti-predator behaviour observed was spatial avoidance (warren abandonment), which seemed to be more accentuated for rabbits who had not previously had contact with foxes in the plot where terrestrial predators were excluded. In both the fenced and the unfenced plot, the differences in the effect of the predator odour between the control and treatment warrens disappeared after cessation of treatment, suggesting a flexible and adaptive behaviour of rabbits to predator cues.

     

Identifying a surrogate metric for monitoring the population status of a secretive habitat specialist,the heath skink Liopholis multiscutata,in south‐eastern Australia

Threatened species that exist in small isolated populations are vulnerable to extinction processes, so effectively monitoring the trajectory of such populations will help determine the most appropriate management actions to combat extinction threats. In this study, we aimed to track the population status of the fossorial heath skink Liopholis multiscutata that is listed as threatened in Victoria, south‐eastern Australia, and exists there as a few small and highly disjunct populations, by using an appropriate surrogate population monitoring metric. This secretive lizard is a habitat specialist, is highly localised in Victoria and lives in warrens in semi‐arid heathland or mallee on large dunes. Survey data, which included every warren and their constituent burrows, as well as an assessment of whether each burrow was ‘active’, were collected for the four known Victorian populations in 2007 and annually during 2014–2018 inclusive. We compared five population indices per monitoring site: number of active warrens (NAW), number of active burrows (NAB), population area for 80% of active warrens (PA80), percentage of warrens that were active (PAW) and average number of active burrows per active warren. The heath skink currently occurs in small populations (8–46 active warrens) and these populations have typically declined over recent years. NAW was the most robust metric; NAB and PA80 did not reveal strong temporal trends. PAW indicated that inactive warrens and burrows persist less than a year and hence may provide information about recent (within months) population changes. It is imperative to establish a material link between the effective monitoring of small, vulnerable populations and the implementation of management actions that benefit such populations. Here, NAW could be used as a long‐term monitoring tool to provide an estimate of the minimum population size of the heath skink at a site. Its use would also ensure continuity in monitoring approaches for the Victorian populations.     

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.     

Burrowing by translocated boodie (Bettongia lesueur) populations alters soils but has limited effects on vegetation

Digging and burrowing mammals modify soil resources, creating shelter for other animals and influencing vegetation and soil biota. The use of conservation translocations to reinstate the ecosystem functions of digging and burrowing mammals is becoming more common. However, in an increasingly altered world, the roles of translocated populations, and their importance for other species, may be different. Boodies (Bettongia lesueur), a commonly translocated species in Australia, construct extensive warrens, but how their warrens affect soil properties and vegetation communities is unknown. We investigated soil properties, vegetation communities, and novel ecosystem elements (specifically non‐native flora and fauna) on boodie warrens at three translocation sites widely distributed across the species’ former range. We found that soil moisture and most soil nutrients were higher, and soil compaction was lower, on warrens in all sites and habitat types. In contrast, there were few substantial changes to vegetation species richness, cover, composition, or productivity. In one habitat type, the cover of shrubs less than 1 m tall was greater on warrens than control plots. At the two sites where non‐native plants were present, their cover was greater, and they were more commonly found on boodie warrens compared to control plots. Fourteen species of native mammals and reptiles were recorded using the warrens, but, where they occurred, the scat of the non‐native rabbit (Oryctolagus cuniculus) was also more abundant on the warrens. Together, our results suggest that translocated boodie populations may be benefiting both native and non‐native flora and fauna. Translocated boodies, through the construction of their warrens, substantially alter the sites where they are released, but this does not always reflect their historic ecosystem roles.     

Is habitat management an effective tool for wild rabbit (<Emphasis Type="Italic">Oryctolagus cuniculus</Emphasis>) population reinforcement?

Wild rabbit scarcity in Spain is a serious problem due to its economic and ecological value; thus, management techniques to reinforce their populations are being implemented. Translocations are traditionally applied but high short-term mortality by predation makes them unsuccessful and increases their biological cost. An alternative to translocation would be to strengthen local reduced populations through habitat management (building artificial warrens and increasing food availability). Here, we test this method to determine its efficiency as an exportable protocol to recover wild rabbit populations. We compare two areas with and without artificial warrens and increased food availability and assess relative rabbit abundance by means of pellet counts. Results show that, during the 2 years following habitat management, rabbit numbers increased in the experimental plot in contrast to the not managed one, suggesting its effectiveness to reinforce low-density rabbit populations.     

Habitat use for warren building by European rabbits (Oryctolagus cuniculus) in relation to landscape structure in a sand dune system

Several conservation efforts are being made to recover European rabbit populations (Oryctolagus cuniculus) on the Iberian Peninsula. Some of them focus on burrow management; others involve building different types of warren. A few studies have examined site selection for warren building, and these studies have considered only warren placement within sites and not the broader area surrounding these locations. The objective of this study was to evaluate how landscape pattern determines habitat selection by rabbits for warren building at different spatial scales. Landscape, home range scale, and microhabitat were the spatial scales used in this study. Warrens were not uniformly distributed over the study area but, rather were concentrated in areas with a high abundance and cover of Retama monosperma and high vegetation cover. Rabbits preferred digging warrens in areas with low fragmentation and where patches are few, large, and contiguous. Based on our results, we suggest that a study of landscape structure should be carried out before design habitat management, recovery or translocation programs. Such studies will need to take into account the physiognomy and size, shape, and continuity of patches in fragmented landscapes. Rabbit conservation programs must address areas that provide not only the maximum potential rate of intake, but also good soil and vegetation cover conditions for warren building and suitable surrounding areas.     

Rabbits and the failure of regeneration in Australian arid zone Acacia

Three experiments are reported concerning the effect of rabbit grazing (Oryctolagus cuniculus L.) upon the recruitment of Acacia seedlings to populations in the South Australian arid zone. In western myall woodland (Acacia papyrocaqsa Benth.) under prevailing rabbit and sheep densities, seedlings exposed to grazing by these two herbivores or to rabbits alone were severely pruned, whereas totally protected seedlings grew unchecked. Seedlings of four Acacia species; A. papyrocarpa, A. oswaldii (F. Muell.), A. kempeana (F. Muell.) and A. burkittii (F. Muell. ex Benth.) were transplanted into four 50 m × 50 m rabbit-proof enclosures. Six rabbits were introduced into each enclosure and within 24 h half of the total seedling population had been grazed. This was at a seedling dry weight ratio of 1|150 000 of the total fodder on offer. In one of the enclosures no seedlings were eaten and there is evidence to suggest that a dense patch of grass had a buffering effect, reducing grazing pressure. Small shoots cut from old Acacia and transferred to the ground throughout 1000 ha of western myall woodland were grazed rapidly near rabbit warrens and progressively less rapidly with increased distance from warrens. The experiments demonstrated that even with the lowered post-myxomatosis population densities, rabbit grazing pressure would significantly affect recruitment in arid zone Acacia populations in the absence of stock.     

Landscape ecology of the burrowing bettong: Warren distribution and patch dynamics in semiarid eastern Australia

Abstract In arid and semiarid Australia fossorial vertebrates have been a major component of the soil biota mediating many fundamental landscape processes. However, many species such as the burrowing bettong (Bettongia lesueur) have become seriously depleted following European pastoral settlement. As ‘landscape engineers’, they were responsible for creating and maintaining a high degree of surface heterogeneity that promoted a diverse and productive herbaceous understorey, particularly in ‘hard‐red’ communities dominated by mulga (Acacia aneura). While their regional extinction has had major impacts by contributing to desertification and loss of biodiversity, relict warrens ‘engineered’ by B. lesueur still remain in certain ecosystems and despite continual weathering, contribute significantly to herbage productivity and species diversity. This paper details the results obtained from a number of field studies aimed at determining the distribution of relict warrens at contrasting scales and their influence on landscape patch dynamics resulting from their impacts on soil nutrients, herbage composition and herbivory. Finally, the conservation implications following the continental extinction of this species and the resulting loss of fundamental ecosystem services, as well as cultural values, are discussed in the context of future re‐introduction efforts.     

Age and season determine European rabbit habitat use in Mediterranean ecosystems

Knowledge about the factors determining habitat use is especially interesting for herbivores living under seasonal climates as they have to deal with food shortage during the drought season. In this context, different-aged individuals are expected to respond differently to seasonal variations because nutritional requirements and predation risk can vary with age. We investigated adult and juvenile European rabbit (Oryctolagus cuniculus) habitat use in a Mediterranean ecosystem of central Spain, during spring, summer and winter. Relationships between adult and juvenile rabbit pellet abundances and 11 environmental variables related to food availability and refuge density were analysed by means of multiple regression, and evaluated using information theory to identify the set of models best supported by the data. Density of warren entrances was the more constant predictor of habitat use for juvenile rabbits in all the seasons. Herbaceous vegetation volume had a negative influence and was the strongest predictor for adult rabbit habitat use in spring and winter. In summer, green vegetation cover became the strongest positive habitat use predictor. These results suggest that adults prefer to forage in low volume swards ensuring a wide sensory range for the detection of approaching predators. However, the arrival of summer and its associated food depletion forces them to shift toward more open productive areas where green vegetation persists, but at the expense of higher predation risk. Seasonal variation induces minor changes in juvenile habitat use due to their strong dependence on warrens. Thus, our results show that rabbit habitat use is influenced by animal age and seasonal variations in resources.     

Hot stuff in the bushes: Thermal imagers and the detection of burrows in vegetated sites

1. Thermal imaging technology is a developing field in wildlife management. Most thermal imaging work in wildlife science has been limited to larger ungulates and surface‐dwelling mammals. Little work has been undertaken on the use of thermal imagers to detect fossorial animals and/or their burrows. Survey methods such as white‐light spotlighting can fail to detect the presence of burrows (and therefore the animals within), particularly in areas where vegetation obscures burrows. Thermal imagers offer an opportunity to detect the radiant heat from these burrows, and therefore the presence of the animal, particularly in vegetated areas. Thermal imaging technology has become increasingly available through the provision of smaller, more cost‐effective units. Their integration with drone technology provides opportunities for researchers and land managers to utilize this technology in their research/management practices.
2. We investigated the ability of both consumer (<AUD$20,000) and professional imagers (>AUD$65,000) mounted on drones to detect rabbit burrows (warrens) and entrances in the landscape as compared to visual assessment.
3. Thermal imagery and visual inspection detected active rabbit warrens when vegetation was scarce. The presence of vegetation was a significant factor in detecting entrances (p < .001, α = 0.05). The consumer imager did not detect as many warren entrances as either the professional imager or visual inspection (p = .009, α = 0.05). Active warren entrances obscured by vegetation could not be accurately identified on exported imagery from the consumer imager and several false‐positive detections occurred when reviewing this footage.
4. We suggest that the exportable frame rate (Hz) was the key factor in image quality and subsequent false‐positive detections. This feature should be considered when selecting imagers and suggest that a minimum export rate of 30 Hz is required. Thermal imagers are a useful additional tool to aid in identification of entrances for active warrens and professional imagers detected more warrens and entrances than either consumer imagers or visual inspection.

     

Rabbit mitochondrial DNA diversity from prehistoric to modern times

The mitochondrial genetic variability in European rabbit (Oryctolagus cuniculus) populations present in Europe and North Africa from 11,000 years ago to the present day has been analyzed using ancient DNA techniques. DNA was extracted from 90 rabbit bones found in 22 archaeological sites dated between the Mesolithic and recent times. Nucleotide sequences present in a variable 233-bp domain of the cytochrome b gene were compared to those present in modern-day rabbits. The results show that the structure of ancient populations of wild rabbit exhibited remarkable stability over time until the Middle Ages. At this time, a novel type of mtDNA molecule abruptly appears into most wild populations studied from France. This mtDNA type corresponds to that currently present in the domestic breeds of rabbit examined so far. The relative rapidity by which this mtDNA type established and its absence in all sites examined before 1,700 years ago lend support to the hypothesis that between 2,000 and 1,000 years ago, man may have favored the development, into all regions of France, of animals carrying this particular mtDNA molecule. The origin of such animals has still to be found: animals previously living outside of France or within France but in very restricted areas? This event was concomitant with the documented establishment of warrens after the tenth century a.d. in Europe.     

Spatial organization and monogamy in the mara Dolichotis patagonum

Maras, Dolichotis patagonum , were observed and radio-tracked in Argentina. They travelled as monogamous pairs that bred either alone at solitary burrows or communally at settlements where up to 29 pairs shared warrens.
Members of a mara settlement grazed within 2.5 km of the communal warrens, using intensively about 1 ha per day, within drifting daily ranges of 11 ha, seasonal ranges of 98 ha and annual ranges of 193 ha.
Their home ranges drifted continuously. Consequently, the long-term movements of neighbouring pairs overlapped substantially, but at any given moment they were territorially spaced.
Monogamous, drifting territoriality is explained by the patchy dispersion of food, the need to minimize interference competition, and a cycle of grazing and fallowing in the use of food plants.
Two hypotheses explaining the adaptive significance of settlements are evaluated: one relates to resource availability (through the indirect effect of ground water and sheep dung on vegetation); and the other relates to predation (through the protective influence of human dwellings). The size of sheep flocks grazing at outstations during January provide a measure of the resource richness of patches where maras graze, and the richness of these patches in the dry season appear to limit the number of maras breeding at each settlement during the following wet season.
Maras face extremes of resource dispersion between the wet and dry seasons: in the former, sparsely dispersed grazing and interference competition favour spacing out and territoriality; in the latter, clumping of resources facilitates pairs congregating in herds around outstations and dry lagoons. Superimposed upon the ecological factors favouring spacing out during the wet season are the sociological factors that cause the maras to den communally. The resulting compromise is a social system unique among mammals.     

Conjugation of unit activity in the visual and sensomotor areas of the rabbit neocortex during a conditioned reflex to sound and light

Conjugation of unit activity in the visual and sensorimotor neocortical areas was studied by means of histograms of cross- and autocorrelation in rabbits with conditioned reflex to light (1st group) and sound (2nd group). Relative number of neurones pairs acting in correlation in the areas remote from each other, in intersignal intervals both before and after stimuli did not differ in the 1st and 2nd groups. At the same time delays in neuronal discharges in one area after the other were different. In the 1st group animals there was a predominance of the number of visual area neurones discharging after sensorimotor with a delay up to 125 ms, in comparison with the number of sensorimotor area neurones discharging after the visual one. In the 2nd group rabbits the number of visual area neurones with such a delay of discharges after sensorimotor was less and, on the contrary, a predominance of sensorimotor area neurones was observed discharging after the visual one. The obtained results allow to suggest that neurones of the visual and sensorimotor neocortex areas form a single functional system in cases when conditioned and unconditioned stimuli are addressed to these areas and when only one of the studied areas is the projection zone for the combined stimuli. Organization of the neurones activity in systems in these two cases is different.     

Spatio-Temporal Factors Shaping Diurnal Space Use by Pygmy Rabbits

Abstract: Factors influencing patterns of space use by pygmy rabbits (Brachylagus idahoensis) are poorly understood. We studied diurnal space use by adult pygmy rabbits during multiple breeding and nonbreeding seasons at 3 sites in the Lemhi Valley, Idaho, USA, during 2004–2005. Pygmy rabbits used larger areas than predicted by allometric models and documented by some previous investigations. Sex and season strongly influenced space use by rabbits. Males used larger home ranges and core areas, more burrow systems, and more widely dispersed burrow systems than did female rabbits. We also documented significant differences among study sites in many movement parameters, which suggested that local resource distribution also might influence how pygmy rabbits use space. Our results indicated that pygmy rabbits use large areas and exhibit seasonal, sex, and site-specific variation in patterns of movement and space use. Therefore, larger areas of habitat may be needed to conserve pygmy rabbits to accommodate seasonal, regional, and potentially annual variation in resource availability and to maintain linkages among populations.