Communal Burrow Research Articles

Activity of tjakura (great desert skinks) at burrows in relation to plant cover and predators.

Increased predation where ground cover is reduced after severe wildfire is increasingly implicated as a factor causing decline of vulnerable prey populations. In arid central Australia, one species detrimentally affected by repeated wildfire is the great desert skink or tjakura (Liopholis kintorei), a distinctive lizard of the central Australian arid zone that constructs and inhabits multi-entranced communal burrows. We aimed to test whether tjakura or predator activity at burrow entrances varied with cover and how tjakura respond to predator presence. Using time-lapse photography, we monitored tjakura and predator activity at the largest entrance of 12 burrows ranging from high (>70%) to low (<50%) cover and at multiple entrances of two other burrows. Overall activity did not vary between burrows with high and low cover. Within burrow systems tjakura were more active at sparsely vegetated entrances, often sitting wholly or partly inside the burrow. However, consistent between and within burrow systems, skinks spent proportionally more time fully outside where cover was higher. Predators-mostly native-were detected at most burrows, with no apparent relationship between predator activity and cover. Skinks also did not appear to modify their activity in response to predator visits. Our results indicate that tjakura may spend more time outside burrow entrances when cover is higher but there was no direct evidence that this related to perceived or real predation risk. Differences in food availability, thermoregulatory opportunities and opportunities for ambush foraging associated with differences in vegetation cover or composition are other factors likely to be important in determining the activity of tjakura at burrows. Our research demonstrates the usefulness of camera traps for behavioural studies of ectothermic burrowing animals. The complex relationships between tjakura activity and vegetation cover thereby revealed, suggest outcomes of fire-mediated habitat change on predator-prey interactions are not easily predictable.

Time tweaks rodents’ subterranean hearing

Scampering through the tunnels of an underground rail station, we might feel like scurrying subterranean rodents, but our well-lit and ventilated tunnels bear little resemblance to the complex communal burrows constructed by rodent excavators. Apart from the lack of oxygen in remote burrow corners, sound carries differently through burrow tunnels than in open air. ‘Frequencies higher than 1 kHz are notably attenuated, even over distances of just a few meters, while lower frequencies are amplified’, says Kai Caspar from the University of Duisburg-Essen, Germany. In addition, the hearing of the rodent species that have descended beneath the surface has altered over time; the question was, had burrowing rodents lost hearing simply through lack of use, or had they actively adapted their hearing to their unique acoustic environment? For example, subterranean rodents could have reduced the sensitivity of their hearing to protect their ears from sounds amplified by tunnels, instead of allowing the sense simply to waste away.To find out, Caspar and his colleagues Alexandra Heinrich, Lea Mellinghaus, Patricia Gerhardt and Sabine Begall (also from the University of Duisburg-Essen) decided to test the hearing of three subterranean species: naked mole rats (Heterocephalus glaber) and Mashona mole rats (Fukomys darlingi), which took to burrowing ∼25 million years ago, and the South American coruro (Spalacopus cyanus), which only adopted a subterranean lifestyle 3.5 million years ago. The team gently anaesthetised the animals, ranging from youngsters to elderly seniors, playing sounds to the slumbering creatures ranging from a low-pitched 30 Hz buzz up to ultrasonic 36 kHz squeals at volumes of 10–80 dB, recording their brainwaves to determine their hearing thresholds at each pitch.And when the researchers compared the rodents’ hearing, it was clear that the hearing of the recent coruro burrowers was far more sensitive than the hearing of the long-term mole-rat excavators. The coruros could still hear ultrasonic sounds up to ∼32 kHz, while the Mashona mole-rats’ hearing tapered out around 4 kHz and the naked mole-rats could barely hear above 6 kHz. Both mole-rat species had lost hearing over the 25 million years since their subterranean shift. Yet, the hearing of all three species was most sensitive to sounds pitched around 1 kHz, which carry most strongly through underground passages. And, when the team recorded conversations between pairs of coruros, Mashona mole-rat duos and a trio of chirping naked mole-rats, the coruros spoke most softly (∼52.6 dB), while the naked mole-rats had the loudest voices ∼58.3 dB, probably to compensate for their poor hearing.So, it seems that rodents don't necessarily lose hearing sensitivity rapidly when they switch to burrowing for a living; coruros haven't done away with their ultrasonic hearing, even though high pitched squeaks barely carry beneath the ground. However, Caspar says, ‘life underground appears to quickly promote a shift of the region of best hearing to low frequencies around 1 kHz’. And, although some aspects of the rodents’ hearing could have dwindled through lack of use, the rodents seem to have tuned their hearing to be most sensitive to a specific range, ‘[possibly] to make the most of the unusual acoustic features of their subterranean homes’, says Caspar.Either way, mole-rat hearing is better than some had thought, in keeping with the creatures’ sociable lifestyle nattering in nest chambers, despite the toll taken over time by their subterranean existence on their appreciation of the squeakier end of the rodent range.

Location of long‐term communal burrows of a threatened arid‐zone lizard in relation to soil and vegetation

AbstractThe great desert skink (Liopholis kintorei) of the Egerniinae subfamily (Reptilia: Scincidae) is a communal burrowing lizard that inhabits arid spinifex grasslands in central Australia. Great desert skink activity is centred in and around the burrows which are inhabited for many years. However, it is not known whether skinks select burrow sites with specific attributes or how continuing occupancy of burrows is influenced by the surrounding habitat; especially post‐fire, when plant cover is reduced. Here, we test whether great desert skink burrows in areas burnt 2 years previously and in longer unburnt areas are associated with particular habitat attributes, and whether there are differences between occupied and recently abandoned burrow sites. Vegetation composition, cover and soil surface characteristics at 56 established great desert skink burrows, including occupied and recently unoccupied burrows, were compared with 56 random nearby non‐burrow control sites. Burrow sites had higher plant cover compared with the surrounding landscape in both recently burnt and longer unburnt areas and were more likely to be associated with the presence of shrubs. Soil stability and infiltration were also higher at burrow sites. However, we found no evidence that burrows with lower cover were more likely to be abandoned. Our results suggest that great desert skinks may actively select high cover areas for burrow construction, although differences between burrow and control sites may also partly reflect local changes to plant cover and composition and soil properties resulting from burrow construction and long‐term habitation of a site. Further research should determine if burrows with shrubs or higher plant cover provide greater protection from predators, more structural stability for burrow construction, increased prey abundance or other benefits. We recommend that maintenance of areas with relatively higher plant cover be prioritized when managing great desert skink habitat.

Taphonomy of modern communal burrow systems of the Plains vizcacha (Lagostomus maximus, Chinchillidae) in the Pampas region of Argentina: implications for the fossil record

The Plains vizcacha (Lagostomus maximus) is one of the largest rodents in South America. They live in communal burrow systems (vizcacheras) shaped by complex subterranean galleries which produce a strong impact on the local landscape. This paper presents the results of an actualistic study conducted with abandoned vizcacheras from the Pampas region of Argentina. The main objective is to evaluate the role of this rodent in the formation of the fossil record. Results indicate that the Plains vizcacha is responsible for the mixing, accumulation, and transport of materials; such as sticks, caliche, dung, feces, and abundant bone remains. Their burrowing activity and the accumulating habits, modifies the landscape, creating environments conducive to the buildup of objects and the reuse by different animals. These characteristics result in very complex associations of materials of different origins; making this rodent an important taphonomic agent with the potential to significantly impact the fossil record.

Belowground herbivory increases vulnerability of New England salt marshes to die‐off

Belowground herbivory is commonly overlooked as a mechanism of top-down control in vegetated habitats, particularly in aquatic ecosystems. Recent research has revealed that increased densities of the herbivorous crab Sesarma reticulatum have led to runaway herbivory and widespread salt marsh die-off on Cape Cod, Massachusetts, USA. Aboveground herbivory is a major driver of this cordgrass habitat loss, but the role of belowground grazing is poorly understood. Sesarma live in communal burrows typically consisting of 1-2 openings and containing 2-3 crabs. However, at die-off sites, burrow complexes can cover > 90% of the low marsh zone, with crab densities as high as 50 crabs/m2 and burrow opening densities of 170 openings/m2. The magnitude of belowground Sesarma activity in association with salt marsh die-off provides an excellent opportunity to extend our knowledge of belowground herbivory impacts in coastal wetlands. Since Sesarma burrows allow access to cordgrass roots and rhizomes, and Sesarma are frequently restricted to burrows by thermal stress and predation, we hypothesized that belowground herbivory would be widespread in die-off areas. We experimentally demonstrate that Sesarma readily eat belowground roots and rhizomes in addition to aboveground cordgrass leaves. We then partitioned above- and belowground herbivory with field manipulations and found that belowground grazing is not only common, but can cause total plant mortality. Additional experiments revealed that plants remain vulnerable to belowground herbivory even after reaching a size refuge from aboveground grazing. This suggests that belowground herbivory contributes to salt marsh die-offs and adds to growing evidence that belowground herbivory is a widespread structuring force in plant communities that can limit habitat persistence.

Is communal burrowing or burrow sharing a benefit of group living in the lesser cavy Microcavia australis?

Burrow systems play an important role in the life of rodents in arid environments. The objectives of this study were to examine the hypothesis that group living is beneficial to the semifossorial rodent, and determine whether Microcavia australis (Geoffroy and d’Orbigny, 1833) burrows communally and/or shares burrow systems. I related the structure of burrow systems to the number of cavies inhabiting them, in two habitats with different soil hardness and different plant cover (El Leoncito and Ñacuñán). El Leoncito has a harsh climate, with lower plant density and softer soil than Ñacñuán. A total of 18 burrow systems were characterized at Ñacuñán, and 12 at El Leoncito. Social groups at El Leoncito have a higher number of individuals than at Ñacuñán, but the structure of burrow systems in softer soil is narrower (small area size), with fewer holes, less slope and depth of galleries, and with no relationship between the number of holes and burrow area. Therefore, considering the development of the burrow system as an indicator of the cost of burrowing, I conclude that communal burrowing to reduce the energetic cost of burrowing per capita is not the primary cause of cavy sociality. M. australis were not active diggers, because digging behaviour was rarely recorded at either site. Burrow systems of cavies persisted over the years of study, occupied by the same cavies and new offspring, and digging new burrow systems and tunnels was a relatively rare event at both sites. Under the burrow-sharing hypothesis, sociality could prevail in M. australis that regularly dig to build and maintain a burrow system which they use for a long time.

Use of Multiple Den Sites by Eurasian Badgers, Meles meles, in a Mediterranean Habitat

Den sites are a conspicuous feature of Eurasian badgers, Meles meles, and in many environments include large communal burrows used by several group members. In Serra de Grândola, southwest Portugal, nine badgers from three social groups were captured and radio collared from 2000 to 2004. A total of 1,787 locations of badgers in their resting sites were registered along with a brief description of the type of site and weather conditions. Resting sites were grouped according to structure (burrows, shrubs, rocks, hollow trees and man-made structures) and function (main, secondary and occasional). Although main setts were the most frequently used shelter (62.25%), an average of 14 (SD 7.55) resting sites were used in each territory. The pattern of use varied seasonally, showing differences according to sex and social group. Overall, females used more than twice as many occasional resting sites as did males. Generally burrows, predominantly main setts, were most frequently used during winter and autumn, whilst non-burrow shelters were preferred during spring and summer, when the weather was hot, dry and not windy. Proximity to food patches had no apparent influence on the location of resting sites. Our results offered no support for the foraging-related hypotheses that multiple resting sites are a means of conserving energy or of maintaining proximity to rich food patches. We suggest that other factors such as thermoregulation needs, disturbance, and reproductive status, could be influencing the observed pattern of resting-site use by badgers in Serra de Grândola.

Cooperative nesting and complex female-biased sex allocation in a tropical allodapine bee

Patterns of sociality and sex allocation are well known for many allodapine bee genera, but have only been described for one species in the genus Macrogalea . Macrogalea is the sister group to the remaining allodapines and is important for inferring plesiomorphic features for the tribe. The present study describes the broad elements of social behaviour and the patterns of sex allocation in an undescribed Macrogalea species from Malawi, and provides the most detailed description of sociality and sex allocation in this genus. This species has large maximum colony sizes (13 adult females) compared to most other allodapines and there is no evidence of reproductive castes. Alloparental care is common and probably unavoidable because brood are progressively reared in a communal burrow where parental care cannot be restricted to filial brood. Cooperative nesting confers substantial benefits in avoiding brood loss, and via enhancement of both per capita brood production and mean pupal weight, but per capita benefits decline after colony sizes exceed three females per nest and total brood size saturates once colony sizes exceed five or six females. All newly eclosed females lay eggs, regardless of body size, but reproduction by older females depends on their relative body size. This suggests the existence of staying incentives for young females, who are potentially valuable alloparents, but that there is reproductive competition among older females who would have little future value as alloparents. The sex ratios are among the most strongly female biased in any bee studied to date, with a colony mean of r ∼ 0.08. There is almost no production of males in colonies with five or fewer adult nestmates, but bias declines very rapidly once colonies exceed this size. This indicates that sex allocation strategies are based on the ability to assess colony size quite accurately, an ability that occurs in several other allodapine genera, and which is likely to be ancestral for the tribe. The present study strengthens recent suggestions that complex sociality and sex allocation patterns are plesiomorphic traits for the allodapines, despite the ubiquity of small colony sizes. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 355‐364. ADDITIONAL KEYWORDS: local resource enhancement ‐ Macrogalea ‐ Malawi ‐ reproductive skew ‐ social evolution.

Vizcacha's Influence on Vegetation and Soil in a Wetland of Argentina

We examined the influence of the plains vizcacha (Lagostomus maximus) on the vegetation structure and the characteristics of soil in a wet grassland area of Argentina. This rodent lives in social groups that share a communal burrow system that is occupied for several generations. The areas in which the vizcacha live and feed are strongly affected by grazing, trampling, and soil removal, exhibiting extensive biopedturbation. To evaluate these effects, we carried out a vegetation survey, along areas extending outward from active vizcacheras, analyzing abundance, plant diversity, vegetation cover, and biomass. We also established soil properties, analyzing physical and chemical variables from the center of the colonies to the grassland matrix. Our results show that vizcachas have indeed affected vegetation, diminishing plant cover and grass biomass in their grazing areas. Vegetation in both areas without animal activity and those of intense grazing was dominated by a few characteristic species. We verified the hypothesis of greatest diversity in areas of moderate disturbance. Perturbed areas had higher cation exchange capacity and electric conductivity and higher clay and sodium contents than the other areas. The rodents' activity introduces a recurrent disturbance factor to the landscape of this region, the outcome of which is the alteration of both the composition and structure of the botanical communities, and some soil properties, scaled in gradients of decreasing effect from the center of a colony to the periphery.

Vizcacha’s Influence on Vegetation and Soil in a Wetland of Argentina

We examined the influence of the plains vizcacha (Lagostomus maximus) on the vegetation structure and the characteristics of soil in a wet grassland area of Argentina. This rodent lives in social groups that share a communal burrow system that is occupied for several generations. The areas in which the vizcacha live and feed are strongly affected by grazing, trampling, and soil removal, exhibiting extensive biopedturbation. To evaluate these effects, we carried out a vegetation survey, along areas extending outward from active vizcacheras, analyzing abundance, plant diversity, vegetation cover, and biomass. We also established soil properties, analyzing physical and chemical variables from the center of the colonies to the grassland matrix. Our results show that vizcachas have indeed affected vegetation, diminishing plant cover and grass biomass in their grazing areas. Vegetation in both areas without animal activity and those of intense grazing was dominated by a few characteristic species. We verified the hypothesis of greatest diversity in areas of moderate disturbance. Perturbed areas had higher cation exchange capacity and electric conductivity and higher clay and sodium contents than the other areas. The rodents’ activity introduces a recurrent disturbance factor to the landscape of this region, the outcome of which is the alteration of both the composition and structure of the botanical communities, and some soil properties, scaled in gradients of decreasing effect from the center of a colony to the periphery.

Patterns of plant species diversity following local extinction of the plains vizcacha in semi-arid scrub

We examined changes in the diversity of herbaceous plant species at colony sites of the plains vizcacha (Lagostomus maximus) following local extinctions of this species in semi-arid scrub of central Argentina. These large rodents live in social groups, share a communal burrow system, and forage in a common home range around the burrow system. Through intense herbivory, vizcachas create large open patches in the understory of a landscape dominated by dense bunch grass and shrubs. In heavily grazed areas at the centers of vizcacha colonies, species richness of forbs was significantly higher than species richness of grasses. In lightly grazed areas at colony edges, both plant groups were equally common. Following local extinction of vizcachas, the number of forb species declined on colony sites as the cover of grasses increased, and within a year grass species were more numerous than forbs at the edges of colonies. Species richness of grasses increased slowly in the areas that had been heavily grazed by vizcachas. Five years after the population crash of vizcachas, species richness of grasses in centers of extinct colonies was less than 50% of the species richness in areas that had been lightly grazed at colony edges. In contrast, grass cover in areas that had been heavily grazed increased to levels similar to the ungrazed matrix within 2-3 years after extinction. Thus, the major transition in physical structure of the plant community occurred much more rapidly than the recovery of plant species richness.

Intergroup and Intragroup Spacing in the Plains Vizcacha, Lagostomus maximus

Direct observations and radiotelemetry were used to study spatial organization of the plains vizcacha ( Lagostomus maximus ) in semi-arid scrub of La Pampa Province, Argentina. Vizcachas live in social groups, the members of which share a communal burrow system and a common home range. Although home range boundaries are not defended, little overlap occurs between home ranges of neighboring groups. All sex and age classes defend the communal burrow system by chasing intruders. Adult males advertise occupancy of the home range with vocalizations and scent marks. Vocalizations were given most frequently during spring, when new immigrants began dispersing into the burrow systems; scentmarking and chases were most frequent during the breeding season. These behaviors occur primarily at burrows.

Social organization and mating system of the plains viscacha (Lagostomus maximus)1

Plains viscachas live in communal burrow systems in groups containing one or more males, several females and immatures. Viscachas forage in groups at night and aggregate underground during the day. All members of a group use burrows throughout the communual burrow system and participate in digging at the burrows. Alarm calls are given primarily by adult males. Allogrooming occurs among all sex‐age classes within a social group but not between members of different social groups. Agonistic interactions occur more often between members of different social groups than within a group.The long‐term social unit of the plains viscacha is the female group. Resident males disappear each year and new males join groups of females. Dominance is absent among females. Agonistic interactions are rare among adult males within a social group and dominance is not clearly evident.

Recruitment, Dispersal, and Group Fusion in a Declining Population of the Plains Vizcacha (Lagostomus maximus; Chinchillidae)

Patterns of emigration, immigration, and colony composition during a population crash are described for the plains vizcacha ( Lagostomus maximus ) in La Pampa, Argentina. The sex ratio of young-of-the-year was slightly male-biased and significantly different from the female-biased sex ratio of adults. Each social group lived in a communal burrow system. Females were recruited into their natal burrow system. Males remained in their natal burrow system up to 27 months, but did not breed there. Tenure of adult females within a social group was longer than tenure of adult males. Females and young moved to other burrow systems as a group, and only when the number of animals became low in their own social group. In contrast, solitary adult males moved into and out of social groups, even when the number of animals in the group was high. Adult males never were present in a social group for more than one breeding season. Inter-group movements occurred in all seasons except winter in both sexes. Dispersal patterns during a population decline, particularly the delay in dispersal of young males and high turnover of individuals within social groups, may differ from movement patterns in habitats with more abundant and stable resources.

Structure of Complex Iguana Nests

showed that up to 8 females may lay eggs in one system and that a system may have up to 24 meters of interconnected underground tunnels with multiple openings to the surface and reach depths of a meter. Two of the systems were more complicated than the others though they did not contain more clutches of eggs. These systems probably represent more than a single season of use. Each female using a multiple burrow system seems to do as much digging as does a female nesting by herself but the nests in a communal burrow system are deeper and probably better protected.

Biogenic Sedimentary Structures Produced by Crabs in Lagoon Margin and Salt Marsh Environments Near Beaufort, North Carolina

ABSTRACT Intertidal burrowing crabs produce distinctive biogenic sedimentary structures in protected lagoon margin and salt marsh environments in the vicinity of Beaufort, North Carolina. Distribution of crabs is determined primarily by substrate characteristics, salinity, and vegetation cover in the intertidal zone. Protected sand beaches and flats are heavily burrowed by the sand fiddler, Uca pugilator, which produces gently curved J-shaped and sharply curved L-shaped burrows 1 to 2 cm in diameter. Larger Y- and U-shaped burrows are formed by the ghost crab, Ocypode quadrata, in the backshore and foredune ridge zones above the high tide line. Salt marshes influenced by normal to near normal marine salinities are burrowed by U. pugilator, U. pugnax, and Sesarma reticulatum. U. pugnax and S. reticulatum burrow in muddy substrates, particularly along tidal creek banks, whereas U. pugilator is restricted to sandy substrate areas. U. pugnax burrows are 1 to 2 cm in diameter and have complex twisting and turning forms. The larger communal burrows of S. reticulatum consist of a complex of interconnected shafts with several oval-shaped surface openings. Panopeus herbstii is often found inhabiting these burrows. In salt marshes where the influence of fresh water is great, U. minax and U. pugnax are the dominant crabs. U. minax forms burrows 2 to 5 cm in diameter with ho ded entrances and long vertical shafts. Intertidal crabs are important agents of bioturbation in the environments that they inhabit. Their burrows have excellent potential for preservation in the sedimentary record. Recognition of the record of biogenic sedimentary structures produced by intertidal crabs would be of significant value in identifying paleoenvironments, fixing ancient lagoon margin and estuarine shorelines, and determining paleosalinities.

THE ONE-MAN CLINIC

<h3>ABSTRACT</h3> In social species where offspring are reared together in communal burrows or similar structures, young animals typically do not engage in between-group contact during their development – a behavioural trait we call ‘offspring with restricted between-group contact’ (ORC). The impact of this trait on the persistence of contagious pathogens that generate lifelong immunity in their hosts is currently unclear. We hypothesize that in populations with ORC, the formation, in groups, of a ‘protective barrier’ of only recovered adults, prevents the transmission of this type of pathogens to the new susceptible hosts (i.e. young animals), thereby increasing the probability of epidemic fade-out. We implement a spatially implicit individual-based Susceptible-Infected-Recovered (SIR) model for a large range of host and pathogen traits and show that the epidemic fade-out probability is consistently higher in populations with ORC, especially when disease spread is fast (high basic reproduction number R₀). We also show that ORC can counteract the cost of group-living in terms of disease risk to a greater extent than variation in other traits. We discuss our findings in relation to herd immunity and outline how they could be used to implement efficient management measures such as vaccinations.