Effects of burrow condition and seed handling time on hoarding strategies of Edward's long-tailed rat (Leopoldamys edwardsi)

Many hoarding rodents use burrows not only for dwelling and protection from natural enemies, but also for food storage. However, little is known how burrows used by scatter-hoarding animals influence their foraging behaviors. In addition, handling time for a given food item has a fundamental impact on hoarding strategies of these hoarding animals: food items with longer handling time are more likely to be hoarded due to increasing predation risk because the animals spend more time outside their burrows if they consumed such food. By providing with two types of artificial burrows (aboveground vs. underground) and two types of food items (i.e. seeds) with contrasting handling times, we investigated how burrow condition and handling time co-influence hoarding strategies of a key scatter-hoarding rodent, Edward's long-tailed rat (Leopoldamys edwardsi) in large enclosures in southwest China. We found that only a few animals larder-hoarded fewer seeds when only aboveground burrows were available, while over 80% of the animals preferred to use the underground burrows and hoard significantly more seeds in the burrows when both aboveground and underground burrows were provided simultaneously. We also found that seed handling time significantly affected hoarding strategies of the animals: they consumed and/or scatter-hoarded more Camellia oleifera seeds with shorter handling time outside the burrow, but consumed and larder-hoarded more Lithocarpus harlandii seeds with longer handling time in underground burrows. Our study indicates that both burrow types and seed handling time have important impacts on hoarding strategies of scatter-hoarding animals.     

Burrow morphology and utilization of the goby (Parapocryptes serperaster) in the Mekong Delta,Vietnam

Some fish species living in mudflats construct burrows for dwelling and hiding. The goby Parapocryptes serperaster is a burrowing fish in mudflats of many estuaries in South East Asia. This study was carried out in the Mekong Delta, Vietnam, to examine burrow morphology and usage by this species. Morphology of the burrows constructed by P. serperaster was investigated by resin castings in situ to obtain the physical structure and configuration of each burrow. Fish from the burrows were caught and measured before burrow casts were made. Fish burrows comprised several openings, a few branching tunnels and multi-bulbous chambers. The surface openings were circular, and the shapes of branching tunnels were nearly round. The burrows had interconnected tunnels and various short cul-de-sac side branches. The burrow structure differed between fish sizes, but burrow dimensions were positively correlated with fish size, indicating that larger fish can make larger and more sophisticated burrow. The burrow structure and dimensions were not different between the dry and wet seasons. Laboratory observations showed that P. serperaster used body movements to dig burrows in the sediment. Burrows could provide a low-tide retreat and protection from predators, but were not used for spawning and feeding for this goby species. This study indicates that the burrowing activity of gobies is an important adaptation for living in shallow and muddy habitats.     

Intertidal burrows of the air-breathing eel goby, <Emphasis Type="Italic">Odontamblyopus lacepedii</Emphasis> (Gobiidae: Amblyopinae)

Odontamblyopus lacepedii inhabits burrows in mudflats and breathes air at the surface opening. Investigations of the intertidal burrows using resin casting demonstrated a highly branched burrow system. The burrows are composed primarily of branching patterns of interconnected tunnels and shafts that communicate into two to seven surface openings. Bulbous chambers (i.e., dilated portions of the burrow) at branching sections of the tunnels or shafts are common features of the burrow. The presence of these chambers accords the fish adequate space to maneuver inside the burrow, and thus constant access to the surface. The combination of all burrow characteristics and previously reported variability in air breathing patterns are ostensibly of selective value for aerial predator avoidance during air breathing in O. lacepedii.     

Burrow construction and behavior of tilefish,Lopholatilus chamaeleonticeps,in Hudson Submarine Canyon

Synopsis During 22 daylight submersible dives in August 1979 numerous juvenile and adult tilefish, Lopholatilus chamaeleonticeps, were observed in and around vertical burrows in the clay substrate of portions of Hudson submarine canyon in depths from 110–230 m. The size and shape of the burrows varied considerably with the smallest juveniles occupying simple vertical shafts in the substrate. Larger fish were found in much larger burrows (up to 4–5 m in diameter and at least 2–3 m deep) that were funnel shaped in cross-section with the upper conical portions containing numerous smaller burrows of associated crabs. The range of burrow sizes observed suggests a regular sequence of burrow construction by tilefish and the associated crabs. Both juvenile and adult tilefish swam into the burrows head first and exited tail first. This behavior, which would preclude the possibility of ambushing prey, and evidence of predation by sharks and other tilefish, suggests that the burrow is a refuge from predators.Tilefish burrows appear to serve as a focus for biological activity. Species associated with the burrows included galatheid crabs, Cancer sp., Acanthocarpus alexandri, Homarus americanus, Heliocolenus dactylopterus and Conger oceanicus. Tilefish may play an important role in structuring outer continental shelf communities. They physically shape their environment and probably have significant biological interactions with the species that associate with their burrows.     

Application of morphologic burrow interpretations to discern continental burrow architects: Lungfish or crayfish?

A methodology for trace fossil identification using burrowing signatures is tested by evaluating ancient and modern lungfish and crayfish burrows and comparing them to previously undescribed burrows in a stratigraphic interval thought to contain both lungfish and crayfish burrows. Permian burrows that bear skeletal remains of the lungfish Gnathorhiza, from museum collections, were evaluated to identify unique burrow morphologies that could be used to distinguish lungfish from crayfish burrows when fossil remains are absent. The lungfish burrows were evaluated for details of the burrowing mechanism preserved in the burrow morphologies together forming burrowing signatures and were compared to new burrows in the Chinle Formation of western Colorado to test the methodology of using burrow signatures to identify unknown burrows.

Permian lungfish aestivation burrows show simple, nearly vertical, unbranched architectures and relatively smooth surficial morphologies with characteristic quasi‐horizontal striae on the burrow walls and vertical striae on the bulbous terminus. Burrow lengths do not exceed 0.5 m. In contrast, modern and ancient crayfish burrows exhibit simple to highly complex architectures with highly textured surficial morphologies. Burrow lengths may reach 4 to 5 m.

Burrow morphologies unlike those identified in Gnathorhiza aestivation burrows were found in four burrow groups from museum collections. Two of these groups exhibit simple architectures and horizontal striae that were greater in sinuosity and magnitude, respectively. One of these burrows contains the remains of Lysoro‐phus, but the burrow surface reveals no reliable surficial characteristics. It is not clear whether Lysorophus truly burrowed or merely occupied a pre‐existing structure. The other two groups exhibit surficial morphologies similar to those found on modern and ancient crayfish burrows and may provide evidence of freshwater crayfish in the Permian.

Burrows from the Upper Triassic Chinle Formation in western Colorado exhibit simple to moderately complex architectural morphologies, ranging from predominantly vertical, unbranched, with little or no chamber development to predominantly vertical, few branches, and with minor chamber development. Surficial burrow morphologies are moderate to highly textured. The burrows have scrape marks, scratch marks, mud and lag‐liners, knobby surfaces, pleopod striae, and body impressions.

Although no fossil remains of the burrowing organism were found within or associated with the Chinle burrows from western Colorado, the similarity of architectural and surficial burrow morphologies to those in the Chinle of Canyonlands, Utah and to modern crayfish burrows, clearly indicates that the Colorado burrows are the product of burrowing crayfish rather than lungfish. Evaluation of burrowing signatures preserved in the architectural and surficial burrow morphologies is a very useful tool to compare and contrast Chinle burrows from different regions on the Colorado Plateau. Documentation of crayfish burrows in the Chinle of Utah and Colorado strongly suggests that other large‐diameter Chinle burrows elsewhere on the Colorado Plateau and in stratigraphically equivalent units may also be the product of crayfish activity.     

Direct evidence of a mesopelagic fish,Melanostigma atlanticum (Zoarcidae) spawning within bottom sediments

Synopsis Adult Melanostigma atlanticum were observed living 15 to 32 cm deep within sediment box cores from 350 m depth in the Laurentian Trough of the Maritime Estuary of the St. Lawrence. The fish were found in fluid pockets or burrows of brown-coloured (oxygenated) silty clay within the anoxic zone of the sediment. In August 1983, four individuals (3 male and 1 female) were recovered from pockets located 15 and 32 cm below the sediment surface. All specimens were greater than 100 mm in length, had empty stomachs, and the female carried no eggs. In July 1985, 6 individuals (1 male and 5 females) were found in a head to tail arrangement within a single burrow at 18–20 cm depth. Three of the females carried eggs, while two appeared to have already released their eggs. A cluster of about 50 large eggs, some of which appeared to have been fertilized, was also found in the burrow. Most of the stomachs were empty, but one contained two copepods, another a proceroid cestode, and others contained between 4–22 parasitic hemiurid trematodes. These observations indicate that burrowing into bottom sediments is important in the reproductive behaviour of M. atlanticum.     

Burrow fractal dimension and foraging success in subterranean rodents: a simulation

For animals that forage underground, the success with whichfood items are located may be closely related to burrow architecture.Fractal dimension, which describes how a burrow explores thesurrounding area in a way that is independent of burrow length,is an obvious choice for a single metric describing burrow shape.Although it is often assumed that burrows of high fractal dimensionwill be associated with greater foraging success, this has notpreviously been demonstrated. In this study, we use computersimulations to study the success with which burrows of differentfractal dimensions locate randomly distributed food items. Inaddition, we examine the effect of different patterns of fooddistribution (in particular the patchiness with which food itemsare distributed) and consider how using different criteria forlocating food items affects the relationship between fractaldimension and foraging success. We conclude that, under a widerange of plausible assumptions about the ways in which subterraneanrodents forage, burrows of high fractal dimension are more successfulat locating food items than burrows of lower fractal dimension.     

Influence of age and environmental factors on burrow-making behavior of the short-tailed cricket,Anurogryllus muticus (De Geer) (Orthoptera: Gryllidae)

For the short-tailed cricket, Anurogryllus muticus, burrow-making behavior is essential. All nymphal instars construct burrows, but in the adult stage the rate of burrowing behavior is age dependent. Increases in photophase and light intensity stimulate burrowing, and the explicit negative phototaxis is correlated with the cricket's inability to exist under dry conditions. Ingestion of substrate during burrow construction may serve to acquire additional moisture. There is no evidence of burrow recognition, and crickets can construct a burrow when needed. The natural distribution of burrows at the plot investigated on Moorea supports the notion thatA. muticus builds burrows where the preferred food plantAlysicarpus vaginalis is most abundant. By minimizing the traveling distance to food sources when foraging they can retreat to their burrow again.     

When seasnake meets seabird: Ecosystem engineering,facilitation and competition

Ecosystem engineers such as burrowing seabirds can increase habitat availability for sympatric taxa – but only if the burrow's owner allows other species to use the newly created shelter site. Our studies on a small Pacific island suggest that an avian burrower (the wedge‐tailed shearwater Puffinus pacificus) is both a facilitator and a competitor for amphibious seasnakes. Video camera inspection of 102 burrows revealed frequent usage of these burrows as retreat sites by the snakes, with Laticauda laticaudata restricted to burrows <4 m from the water's edge, whereas Laticauda saintgironsi often used burrows further inland. Snakes never occupied burrows that contained adult shearwaters, suggesting active burrow defence by the birds. Model snakes that we inserted into burrows were attacked, especially on the head and upper body, and we found one snake pecked to death outside a burrow. Wedge‐tailed shearwaters act as facilitators, creating a thermally favourable microhabitat and substantially enhancing habitat suitability for snakes; but they are also competitors, aggressively competing with snakes for occupancy of the resource that has been created.     

Aggregation in a Desert Tenebrionid Beetle: A Cost/Benefit Analysis

Parastizopus armaticeps (Coleoptera: Tenebrionidae), a nocturnal fossorial detritivore inhabiting southern Kalahari dunes, aggregates in burrows during the day. Group size increases during drought but 25% of beetles are still found alone or in pairs. During drought, beetles from large groups leave burrows after sunset synchronously and carlier than pairs and single animals and earlier than beetles of any group size after rain. Detritus from the beetles' major foodplant is scarce and food competition high. Beetles emerging early preferentially select and carry high-quality transportable items into burrows to eat (forage); late-emerging ones feed on the low-quality large twigs on the surface. Foraging is shown to be a strategy to secure food items against surface competitors, not one to reduce body water loss during surface exposure. The costs and benefits of group vs. solitary lifestyles and alternate hypotheses for early and synchronous emergence were tested experimentally. Grouped beetles had lower body water loss rates but, due to competition with burrow mates, higher feeding costs than single ones. It is hunger that advances and thus synchronizes emergence time, not social facilitation. Field data support a model predicting that, for maximal benefits, beetles should alternate between solitary and group life at optimal time intervals.     

Developmental morphology of the cottid fish Pseudoblennius marmoratus

Embryonic, larval, and juvenile development of a Japanese cottid fish Pseudoblennius marmoratus is described from laboratory-reared specimens. Eggs of P. marmoratus resembled those of two congeners, Pseudoblennius cottoides and Pseudoblennius percoides, but differed in their smaller diameter and yolk color. Although the larvae and juveniles of P. marmoratus were also similar to them in general morphology, the former differed in the lengths of newly hatched larvae, pigmentation patterns, number of pectoral fin rays, and dorsal fin spine elongation.     

Selection of food patches by sympatric herbivores in response to concealment and distance from a refuge

Small herbivores face risks of predation while foraging and are often forced to trade off food quality for safety. Life history, behaviour, and habitat of predator and prey can influence these trade‐offs. We compared how two sympatric rabbits (pygmy rabbit, Brachylagus idahoensis; mountain cottontail, Sylvilagus nuttallii) that differ in size, use of burrows, and habitat specialization in the sagebrush‐steppe of western North America respond to amount and orientation of concealment cover and proximity to burrow refuges when selecting food patches. We predicted that both rabbit species would prefer food patches that offered greater concealment and food patches that were closer to burrow refuges. However, because pygmy rabbits are small, obligate burrowers that are restricted to sagebrush habitats, we predicted that they would show stronger preferences for greater cover, orientation of concealment, and patches closer to burrow refuges. We offered two food patches to individuals of each species during three experiments that either varied in the amount of concealment cover, orientation of concealment cover, or distance from a burrow refuge. Both species preferred food patches that offered greater concealment, but pygmy rabbits generally preferred terrestrial and mountain cottontails preferred aerial concealment. Only pygmy rabbits preferred food patches closer to their burrow refuge. Different responses to concealment and proximity to burrow refuges by the two species likely reflect differences in perceived predation risks. Because terrestrial predators are able to dig for prey in burrows, animals like pygmy rabbits that rely on burrow refuges might select food patches based more on terrestrial concealment. In contrast, larger habitat generalists that do not rely on burrow refuges, like mountain cottontails, might trade off terrestrial concealment for visibility to detect approaching terrestrial predators. This study suggests that body size and evolutionary adaptations for using habitat, even in closely related species, might influence anti‐predator behaviors in prey species.     

Brood burrow construction and brood care by Heliocopris japetus (Klug) and Heliocopris hamadryas (Fabricius) (Coleoptera, Scarabaeidae)

• 1 Brood burrow construction and brood care were studied by excavating burrows of different ages and by re-excavating certain burrows after a defined interval.
• 2 Brood burrows consisted of tunnels running via an upper chamber to a lower chamber 0.55–1.3 m below ground.
• 3 The female excavated the upper chamber, filled it with dung, then excavated the lower chamber and packed it with dung from the upper chamber.
• 4 Soil was removed from around the dung to give adungmasslying free in the lower chamber. The male was present during and just before this stage, and may cooperate in pushing soil out through the tunnel. Later the tunnel was filled with soil, excluding the male from the lower chamber.
• 5 The female formed the dung mass into balls each of which contained an egg. Development of the larvae led to an expansion at the upper pole, producing a pear shape. Third instar larvae were found in pears with a soil covering.
• 6 In the case of H.japetus the pears later became soil-covered balls containing the new adults, and the female remained in the chamber and died after the young had emerged.
• 7 The push-ups of H.japetus and of H.hamadryas were distinguishable, reflecting slight differences in the technique of burrow construction. H.hamadryas burrows were deeper and contained smaller brood balls.

     

Obligate crayfish burrow use and core habitat requirements of crawfish frogs

Crawfish frogs (Lithobates areolatus) have experienced declines across large portions of their former range. These declines are out of proportion to syntopic wetland-breeding amphibian species, suggesting losses are resulting from unfavorable aspects of non-breeding upland habitat. Crawfish frogs get their common name from their affinity for crayfish burrows, although the strength of this relationship has never been formally assessed. We used radiotelemetry to address 4 questions related to upland burrow dwelling in crawfish frogs: 1) what burrow types are used and how do they function to affect crawfish frog survivorship; 2) what are the physical characteristics and habitat associations of crawfish frog burrows; 3) what are the home range sizes of crawfish frogs when burrow dwelling; and 4) where are crawfish frog burrows situated with respect to breeding wetlands? We tracked crawfish frogs to 34 burrows, discovered another 7 occupied burrows, and therefore report on 41 burrows. Crawfish frogs exclusively occupied crayfish burrows as primary burrows, which they inhabited for an average of 10.5 months of the year. With one exception, crawfish frogs also used crayfish burrows as secondary burrows—temporary retreats occupied while exhibiting breeding migrations or ranging forays. Burrows were exclusively located in grassland habitats, although crawfish frogs migrated through narrow woodlands and across gravel roads to reach distant grassland primary burrow sites. Home range estimates while inhabiting burrows were 0.05 m² (the area of the burrow entrance plus the associated feeding platform) or 0.01 m³ (the estimated volume of their burrow). Crawfish frog burrows were located at distances up to 1,020 m from their breeding wetlands. To protect crawfish frog populations, we recommend a buffer (core habitat plus terrestrial buffer) of at least 1.2 km around each breeding wetland. Within this buffer, at least 3 critical habitat elements must be present: 1) extensive grasslands maintained by prescribed burning and/or logging, 2) an adequate number of upland crayfish burrows, and 3) no soil disturbance of the sort that would destroy crayfish burrow integrity. © 2012 The Wildlife Society.     

Microscale oxygen distribution in various invertebrate burrow walls

Profiles of dissolved oxygen were measured in pore waters of unburrowed sediment and the burrow walls of seven invertebrate dwellings. Burrows studied include those of Corophium volutator, Heteromastus filiformis, Arenicola marina, Saccoglossus bromophenolosus, Clymenella sp., Hemigrapsus oregonensis and Cirriformia luxuriosa all from mudflats in Willapa Bay, Washington. These animals comprise a range of burrow architectures ranging from simple, unlined burrows to more complex, mucous lined burrows. Oxygen penetrated unburrowed sediment between depths of 0.4–2.6 mm, whereas oxygen penetrated the burrow walls from 0.3 mm to 2.3 mm. Three groups of burrows are recognized based on the oxygen diffusive properties relative to the unburrowed sediment including those that: (1) slightly impeded oxygen penetration, (2) clearly inhibited oxygen penetration, and (3) enhanced oxygen penetration. Differences in the diffusive properties of the burrow wall are related to the burrow microstructure and presumably the microbial communities living within the burrow microenvironment. The results of this study suggest that burrow shape and burrow‐wall architecture may play an important role in controlling the diffusion of oxygen, and possibly of other dissolved gases (i.e. CO₂, H₂S). The results further demonstrate that simplified assumptions (i.e. that bioturbation uniformly enhances oxygen diffusion into suboxic and anoxic sediments), while requisite for numerical modelling, are not necessarily representative of field data.     

Burrow defense behaviors in a sand-bubbler crab, Scopimera globosa, in relation to body size and prior residence

The burrow defense behaviors in a sand-bubbler crab, Scopimera globosa, living on a tidal flat, were experimentally examined. Body size and prior residence influenced the results of struggles for the burrows, and large individuals or the burrow owners won in most cases when the intruders were not significantly larger than the owners. Most large owners defended their burrows by directly fighting their opponents. On the other hand, small owners defended their burrows in three different ways. (1) Owners fought directly against same-sized or smaller intruders. For larger intruders, (2) most owners returned to their burrows when the owner was nearer to the burrow than the intruder (returning behavior), and (3) owners sat motionless when the intruder was nearer to the burrow than the owner (sitting behavior). Success ratios of the three types of burrow defense were 38.2%, 88.5%, and 100%, respectively. It was considered that sitting behavior of the cryptically colored S. globosa has evolved because intruders cannot see motionless owners and consequently cannot detect the owner's burrow. Received: October 6, 2000 / Accepted: January 22, 2001     

Depth of artificial Burrowing Owl burrows affects thermal suitability and occupancy

Many organizations have installed artificial burrows to help bolster local Burrowing Owl (Athene cunicularia) populations. However, occupancy probability and reproductive success in artificial burrows varies within and among burrow installations. We evaluated the possibility that depth below ground might explain differences in occupancy probability and reproductive success by affecting the temperature of artificial burrows. We measured burrow temperatures from March to July 2010 in 27 artificial burrows in southern California that were buried 15–76 cm below the surface (measured between the surface and the top of the burrow chamber). Burrow depth was one of several characteristics that affected burrow temperature. Burrow temperature decreased by 0.03°C per cm of soil on top of the burrow. The percentage of time that artificial burrows provided a thermal refuge from above‐ground temperature decreased with burrow depth and ranged between 50% and 58% among burrows. The percentage of time that burrow temperature was optimal for incubating females also decreased with burrow depth and ranged between 27% and 100% among burrows. However, the percentage of time that burrow temperature was optimal for unattended eggs increased with burrow depth and ranged between 11% and 95% among burrows. We found no effect of burrow depth on reproductive success across 21 nesting attempts. However, occupancy probability had a non‐linear relationship with burrow depth. The shallowest burrows (15 cm) had a moderate probability of being occupied (0.46), burrows between 28 and 40 cm had the highest probability of being occupied (>0.80), and burrows >53 cm had the lowest probability of being occupied (<0.43). Burrowing Owls may prefer burrows at moderate depths because these burrows provide a thermal refuge from above‐ground temperatures, and are often cool enough to allow females to leave eggs unattended before the onset of full‐time incubation, but not too cool for incubating females that spend most of their time in the burrow during incubation. Our results suggest that depth is an important consideration when installing artificial burrows for Burrowing Owls. However, additional study is needed to determine the possible effects of burrow depth on reproductive success and on possible tradeoffs between the effects of burrow depth on optimal temperature and other factors, such as minimizing the risk of nest predation.     

Redescription of the festive snailfish, Liparis marmoratus (Scorpaeniformes: Liparidae), with a new record from the northern Bering Sea

The liparid fish Liparis marmoratus is redescribed based on examination of two syntypes and two additional specimens. Liparis marmoratus is distinguished from other Sea of Okhotsk and Bering Sea Liparis by having a wide head, small mouth, short blunt snout, closely set chin pores, small gill opening, a firm body with slightly developed subcutaneous gelatinous tissue, a nearly horizontal dorsal body profile, and unique body markings and coloration. Liparis marmoratus was previously known only from the Sea of Okhotsk. A Liparis specimen collected near St. Lawrence Island in the northern Bering Sea was compared to the type series and determined to be L. marmoratus. Received: April 4, 2000 / Revised: November 2, 2000 / Accepted: January 11, 2001     

Estimation of N2 fixation based on differences in the natural abundance of 15N among freshwater N2-fixing and non-N2-fixing algae

The hypothesis that small mammal burrows can increase the amount of water infiltrating into the soil profile was tested. The amount of water added to the soil profile from spring recharge in areas adjacent to ground squirrel (Spermophilus townsendii and S. elegans) burrows was compared to nearby areas without burrows. Recharge amounts in burrow areas were significantly higher than nonburrow areas. An average of 21% more of the winter precipitation infiltrated into the soil near burrows. The amount of recharge was also found to be positively related to burrow density. Burrows also affected the distribution of the recharge by adding significantly more water to the deeper portions (>50 cm) of the soil profile.     

The microenvironment of house mice on Marion Island (sub-Antarctic)

On Marion Island, house mice ( Mus musculus) establish burrow systems that range from unbranched corridors 0.5 m long with a single chamber (in some instances without a chamber) to complexly branched systems extending over an area of up to 4 m² and containing up to four chambers. Total underground area occupied by burrow systems (chambers plus corridors) was from 5 to 23 m² ha^-1, corresponding to burrow-system volumes of 250-1,300 dm³ ha^-1. In autumn, about three-quarters of chambers contained small food caches. Most (87%) entrances to burrow systems faced away from prevailing winds, especially winds that bring snow, hail or rain. Seasonal and diurnal temperature variations in burrows are considerably dampened (daily minimum in burrows seldom drops below 2°C), compared with the air just above the vegetation canopy. Over the whole year, total night-time warmth in a burrow (heat sum, 24,883 degree hours) was 53% greater than at the top of the canopy (16,317 degree hours). Burrows' entrances are generally connected above ground by runways (paths and tunnels through the vegetation). Runways also represent a warmer environment than the air above the canopy during the breeding season at night (13,466 degree hours at the runway surface compared with 11,900 degree hours at the top of the canopy). House mice, which are living close to their physiological limits, temperature-wise, on Marion Island thus evade the worst extremes of the island's climate by constructing burrows and above-ground runways and this is an important factor in their survival.