Burrow Abundance Research Articles

Links between riparian characteristics and the abundance of common wombat (Vombatus ursinus) burrows in an agricultural landscape

Agricultural riparian zones are often vulnerable to weed invasion and degradation of the physical streambank character through the trampling of livestock. Riparian zone restoration seeks to improve habitat biodiversity, minimise streambank erosion and improve water quality. In order for this to be effective land managers need to broadly understand the connections between riparian systems and adjoining agricultural ecosystems and to understand the habitat requirements of wildlife species adapted to the evolving riparian landscape. Common wombats (Vombatus ursinus) are abundant in the riparian agricultural landscapes of south-eastern Australia, but there is concern about their persistence in other landscapes. To understand the importance of riparian characteristics for wombats, we examined five physical and five vegetative characteristics associated with abundance of wombat burrows in the riparian zone of an agricultural landscape in south-eastern New South Wales, using two independent datasets. The abundance of wombat burrows increased substantially with increasing shrub cover in both datasets. There was weaker but consistent support for an association between wombat burrows and stream order and vegetation width. There were more burrows per metre by high than low order streams and burrows were most abundant at an intermediate vegetation width. In one of the two datasets, burrow abundance declined as the proportion of native shrubs in the shrub layer increased. As wombats are generally limited to riparian buffers in agricultural landscapes, these results are important as a first step toward managing and restoring the riparian zone. Restoration strategies, for example, may need to consider retaining patches of shrubs, even if they are weeds, whereas native shrubs are established in interspersed patches along larger rivers, in order to maintain suitable wombat habitat.

Comparison of methods for estimating abundance of gopher tortoises

Estimates of abundance of threatened and endangered species are crucial for monitoring population status and recovery progress. For most wildlife species, multiple abundance estimation methods are available and the choice of method should depend on cost and efficacy. We field-tested the cost and efficacy of line transect, total count, sample count, and double observer methods for estimating abundance of gopher tortoise (Gopherus polyphemus) burrows in two habitats that differed in vegetation density (sparse and dense) at the Ordway-Swisher Biological Station in north-central Florida. In the dense vegetation stratum, density of burrows estimated using the line transect method (8.58 ± 0.94 burrows ha−1) was lower than that obtained from the total count method (11.33 burrows ha−1). In the sparse vegetation stratum, estimated burrow density using the line transect method (11.32 ± 1.19 burrows ha−1) was closer to the burrow density obtained from the total count method (13.00 burrows ha−1). Density of burrows estimated using the double observer method was identical to that obtained from the total count method in dense vegetation stratum, but slightly greater than that obtained from the total count method in sparse vegetation stratum. Density of burrows estimated using the sample count method varied widely depending on the proportion of plots sampled. The cost of sampling as well as estimates of burrow density varied with habitat type. The line transect method was the least costly of the methods, and we were able to sample a larger effective area with the same effort. Using burrow cameras and patch occupancy modeling approach, we also estimated the probability of burrow occupancy by gopher tortoises (active: 0.50 ± 0.09; inactive: 0.04 ± 0.04), and used these values to estimate abundance of gopher tortoises. Using estimates of burrow abundance based on the line transect method, density of gopher tortoises was 2.75 ± 0.74 ha−1 in the sparse vegetation stratum. We recommend that gopher tortoise monitoring programs use rigorous methods for estimating burrow abundance (e.g., line transect methods) and the probability of burrow occupancy by gopher tortoises (e.g., patch occupancy modeling approach).

Vertebrate burrows in late Pleistocene paleosols at Korean Palaeolithic sites and their significance as a stratigraphic marker

A vertebrate burrow-bearing layer of late Pleistocene age is commonly found at many Paleolithic archaeological sites in Korea. The burrows are straight to slightly curved in horizontal (plan) view and gently inclined in lateral (sectional) view. They are interpreted as having been produced by rodent-like mammals based on their size and architecture. The significance of such burrow-bearing layers as a characteristic stratigraphic marker unit is demonstrated by high burrow abundance, consistent stratigraphic position, lack of stratigraphic recurrence at these sites, and widespread geographic extent. Three dating methods, tephrochronology, radiocarbon, and OSL dating, were used to infer the age of these burrow-bearing layers. The dating results indicate that they were formed between ca. 40,000 and 25,000 yr (MIS 3−2), and this suggests that this layer can be used as a stratigraphic time-marker in late Pleistocene paleosol sequences for this region.

Predictive habitat modelling for the population census of a burrowing seabird: A study of the endangered Cook’s petrel

Inaccurate population data remain a major problem in the conservation of burrow-nesting Procellariiform seabirds. We evaluated the potential of predictive habitat modelling, in contrast with traditional surface-area based strategies, to estimate the population size of the endangered Cook’s petrel ( Pterodroma cookii), breeding on one of two islands in New Zealand. Generalised linear models of burrow abundance using topographic data collected in the field, or extracted from Geographic Information System layers, were developed, and the final model applied to Geographic Information Systems-derived datasets in a population analysis. To compare this result with traditional census methods, population estimates were also calculated by averaging burrow densities across the total area available (simple model) and within vegetation zones (habitat-area model). Results of all models were scaled using rigorously collected burrow occupancy data. The final model, based upon altitude, slope, and distance from ridgelines, explained 31% of the variance in Cook’s petrel burrow abundance and showed an enhanced predictive fit compared with the two area-based models. This model indicated that annually 286,000 (95% confidence interval: 213,000–413,000) pairs of Cook’s petrel breed on Little Barrier Island, approximately six times that previously suggested. Population estimates based on simple and habitat-area models were less accurate, being 10% and 30% greater than the predictive model estimate, respectively. This study underlines the need for accurate population estimates for burrowing seabird taxa by presenting a major population revision for the Cook’s petrel. Predictive habitat models, employing rigorously collected data, offer an improvement on more traditional population census methodologies that are susceptible to scale-induced bias.

Effects of Land Use on the Distribution of Three Species of Armadillos in the Argentinean Pampas

We evaluated the effects of land use on the distribution of 3 sympatric species of armadillos, Chaetophractus villosus, C. vellerosus, and Dasypus hybridus, on 34 farms in the eastern Pampas. We characterized 4 soil and vegetation variables around each burrow located during surveys of these farms, and related burrow abundance to 10 variables used to characterize each farm. C. vellerosus was the most specialized, using primarily native woodlands and areas with calcareous soil. D. hybridus was associated with natural grasslands and avoided cultivated pastures, and was negatively related to the number of dogs that lived on the farms. C. villosus, the most abundant species, was found in all 4 types of habitats, but its distribution depended on the intensity of hunting on each farm.

Quantification of Ammonia-Oxidizing Bacteria and Factors Controlling Nitrification in Salt Marsh Sediments

To elucidate the geomicrobiological factors controlling nitrification in salt marsh sediments, a comprehensive approach involving sediment geochemistry, process rate measurements, and quantification of the genetic potential for nitrification was applied to three contrasting salt marsh habitats: areas colonized by the tall (TS) or short (SS) form of Spartina alterniflora and unvegetated creek banks (CBs). Nitrification and denitrification potential rates were strongly correlated with one another and with macrofaunal burrow abundance, indicating that coupled nitrification-denitrification was enhanced by macrofaunal burrowing activity. Ammonia monooxygenase (amoA) gene copy numbers were used to estimate the ammonia-oxidizing bacterial population size (5.6 x 10(4) to 1.3 x 10(6) g of wet sediment(-1)), which correlated with nitrification potentials and was 1 order of magnitude higher for TS and CB than for SS. TS and CB sediments also had higher Fe(III) content, higher Fe(III)-to-total reduced sulfur ratios, higher Fe(III) reduction rates, and lower dissolved sulfides than SS sediments. Iron(III) content and reduction rates were positively correlated with nitrification and denitrification potential and amoA gene copy number. Laboratory slurry incubations supported field data, confirming that increased amounts of Fe(III) relieved sulfide inhibition of nitrification. We propose that macrofaunal burrowing and high concentrations of Fe(III) stimulate nitrifying bacterial populations, and thus may increase nitrogen removal through coupled nitrification-denitrification in salt marsh sediments.

Ichnology of a late Pleistocene ichnofabric, Nebraska, USA

Abstract The “Citellus zone” is a regionally extensive biohorizon with abundant burrows and remains of ground squirrels (Spermophilus=“Citellus”) and other rodents. One hundred and four outcrops were evaluated to determine the stratigraphic relationship of the zone and to confirm its geographic extent. “Citellus zone” bioturbation exists over the entire 1700-km2 study area in south-central Nebraska and was synchronous with mid-Wisconsinan Gilman Canyon loess deposition (Altonian and Farmdalian Substages), since burrow abundances are constant throughout its thickness. Calculations based upon maximum burrow abundance and the known digging rates of the burrowers confirm that the zone could have been produced during Gilman Canyon deposition. In the lower part of the zone, decline in burrow abundance with increasing depth in the Loveland Formation (Sangamonian and Illinoian Stages) suggests that this unit predates burrowing. Thomomys-sized geomyid trace fossils become proportionally less common with increasing depth, consistent with the transition from fodinichnia to domichnia, as Spermophilus richardsonii-sized spermophiline and prairie dog domichnia become more common.

Ichnology of a late Pleistocene ichnofabric, Nebraska, USA

The “ Citellus zone” is a regionally extensive biohorizon with abundant burrows and remains of ground squirrels ( Spermophilus=“ Citellus”) and other rodents. One hundred and four outcrops were evaluated to determine the stratigraphic relationship of the zone and to confirm its geographic extent. “ Citellus zone” bioturbation exists over the entire 1700-km 2 study area in south-central Nebraska and was synchronous with mid-Wisconsinan Gilman Canyon loess deposition (Altonian and Farmdalian Substages), since burrow abundances are constant throughout its thickness. Calculations based upon maximum burrow abundance and the known digging rates of the burrowers confirm that the zone could have been produced during Gilman Canyon deposition. In the lower part of the zone, decline in burrow abundance with increasing depth in the Loveland Formation (Sangamonian and Illinoian Stages) suggests that this unit predates burrowing. Thomomys-sized geomyid trace fossils become proportionally less common with increasing depth, consistent with the transition from fodinichnia to domichnia, as Spermophilus richardsonii-sized spermophiline and prairie dog domichnia become more common.

Impact of tillage practices and burrows of a native Australian anecic earthworm on soil hydrology

Anecic earthworms are rare in Australian soils and potential benefits of introduction of exotic anecic earthworms have been suggested. The contribution of the native anecic earthworms to soil hydrology is unknown. The impact of tillage on the abundance and continuity of burrows formed by the native earthworm, Spenceriella hamiltoni (Fletcher) and consequent effect on hydrology were investigated in a red earth (Ultisol) in the Central Tablelands of New South Wales, Australia. On the permanent pasture site, the burrows occurred at a density of 157 (±65) m −2, had an average diameter of 6.0 mm (S.D.=1.6), and a predicated median length of 1.8 m. Dye infiltration studies showed that only 53% of the burrow openings were conducting and therefore available for infiltration under high rainfall conditions. It was estimated that a single burrow over an area of one square metre had an infiltration rate of 1.9 times that of the soil matrix (6.7 mm h −1 versus 3.6 mm h −1). Prediction using the rainfall characteristics of the region and the existing density of transmitting burrows under permanent pasture suggests that runoff should be a rare event (<once every 100 years). While earthworm burrow density under no-tillage (NT) cropping was similar to that found under permanent pasture, 3 years of conventional tillage (CT) involving discing reduced transmitting burrows by nearly 90% (to only 10 m −2) and this had the effect of a 8.3-fold reduction in maximum infiltration rate of the soil, thereby significantly increasing the likelihood of runoff and erosion.

Increased Lesser Earless Lizard (Holbrookia maculata) Abundance on Gunnison's Prairie Dog Colonies and Short Term Responses to Artificial Prairie Dog Burrows

Our studies of the association between the lesser earless lizard (Holbrookia maculata) and Gunnison's prairie dogs (Cynomys gunnisoni) revealed: (1) the lesser earless lizard was more abundant on prairie dog colonies than off; (2) lesser earless lizard abundance was positively correlated with prairie dog burrow abundance; (3) lesser earless lizards responded positively to artificial burrows created on noncolonized areas; and (4) lesser earless lizards used prairie dog burrows as refuges from predators; however, the relative use of burrows was greatest at high and low temperature extremes. Although prairie dogs alter habitat in many ways, our study suggests that burrows are an important mechanism involved in the association between the lesser earless lizard and Gunnison's prairie dogs.

Influence of abundance of small-mammal burrows and conspecifics on the density and distribution of spotted salamanders (Ambystoma maculatum) in terrestrial habitats

Spotted salamander (Ambystoma maculatum) distributions were studied within eighteen 272-m2 field enclosures in upland deciduous forest adjacent to two breeding ponds. The enclosures were subsequently used in experiments involving (i) removal of small-mammal burrows to determine if burrow abundance influenced salamander density and (ii) manipulation of salamander densities to determine if increased density was associated with decreased growth, fecundity, or probability of re-emerging to breed. Mean density of salamanders wintering in enclosures &lt;65 m from the breeding ponds was 1.0/100 m2 (SD = 1.1/100 m2, n = 17, range = 0–4.0/100 m2). Density declined as distance to the nearest breeding pond increased, and the sex ratio was skewed sharply toward males (8:1) wintering close (&lt;65 m) to the pond but not farther from the pond (1:1). Males residing within the enclosures weighed more than males wintering farther from the breeding ponds. Migrating salamanders were over 3 times more likely to leave burrow-removal plots than control plots prior to the summer inactive period. Salamanders housed at high density (15/enclosure) were less likely to re-emerge to breed than were salamanders housed at low density (5/enclosure), but we observed no effects on growth or fecundity. Results suggest that conspecific distribution and burrow availability might affect the density of spotted salamanders within terrestrial habitats.

Density affects female and male mate searching in the fiddler crab, Uca beebei

In most species, only one sex searches for mates while the other waits. Models of sex-specific mate-searching behavior predict single-sex searching, but the factors that determine which sex searches are not understood. In this study, we examine the effects of den- sity and predation risk on mate-searching behavior in the fiddler crab Uca beebei. U. beebei is one of the few fiddler-crab species in which both sexes search for mates. In a field experiment conducted in Panama, we manipulated crab density and perceived predation risk in replicate plots. Females searched more and males searched less at high densities. At high levels of per- ceived predation risk, both sexes similarly reduced their search rates. Observations of plots that naturally varied in crab density show that females were more likely to search for mates in areas of higher density, where there were more males. Females may preferentially search for mates in high-density areas because the abundance of nearby burrows, into which they can run to escape preda- tors, decreases their costs of searching and because the abundance of males and male burrows facilitates com- parisons and thus may increase their benefits from searching. Males at high densities decrease their mate- searching rate perhaps in response to the increase in fe- male searching and to the corresponding increase in the intensity of their competitors' mate-attraction signals.

Faunal burrows as indicators of paleo-vegetation in eastern Washington, USA

The Palouse loess deposits in the Pacific Northwestern United States contain buried paleosols with distinctive biological fabrics. The Washtucna Soil, formed 40,000–15,000yr ago during the last full glacial, contains up to 90% by volume distinctive cylindrical pedotubules that are 1–2cm in diameter formed by burrowing fauna. The overlying post-glacial loess and modern surface soils that support perennial grasslands lack these cylindrical burrows. We investigated the paleoecological significance of the burrows. Observations of several types of burrowing fauna under native vegetation indicated that nymphs of cicadas (Homoptera: Cicadidae) are responsible for cylindrical, back-filled burrows that match those in the Washtucna Soil. We measured the abundance of active cicada burrows in soils in four native vegetation zones (Soil sites), establishing that cicada burrows comprise 19% of the rooting zone volume in sagebrush steppe, but just 1–3% of the rooting zone volume in bunchgrass steppe, meadow steppe and coniferous forest. This suggests strongly that abundant cicada burrows in paleosols are a proxy for the geographic extent of plant communities that contained sagebrush. To assay the activity of cicada nymphs through time, we measured burrowed volume by depth from the soil surface down through the Washtucna Soil (i.e. from the present to ca. 40,000yrbp) at five stratigraphic research sites (Paleosol sites). Cicada-burrowed volume is generally less than 5% in the rooting zone of the surface soils and throughout Holocene loess, but is up to 94% in the rooting zone of the Washtucna Soil at Paleosol sites that currently support bunchgrass steppe outside the present-day sagebrush steppe zone. Cicada host preferences in vegetation zones today suggest that sagebrush was the dominant shrub as the Washtucna Soil formed. From this reconstruction, combined with information from studies of pollen and plant opal, we infer that periglacial steppe plant communities dominated by sagebrush spread, from 40,000 to 15,000yrbp, into areas of the Columbia Plateau that support bunchgrass steppe, meadow steppe, and even some coniferous forest today. Trace fossils of soil fauna in paleosols are indicators of fluctuations in biological activity in response to climatic changes of the Quaternary Period in Palouse loess deposits.

The effect of biogenic irrigation intensity and solute exchange on diagenetic reaction rates in marine sediments

The activities of infaunal macrobenthos strongly influence the pathways, rates, and extent of organic matter remineralization and associated reactions in marine sediments. Solute transport during irrigation is a particularly important process that stimulates microbial activity and net remineralization, both within and adjacent to the bioturbated zone. Part of the stimulation proximal to the bioturbated zone is due to redox oscillation and oxidant supply during transport, but part of both the near and far-field effects are a result of other factors. Experiments designed to simulate different degrees of diffusive exchange, and thus infaunal abundances or activity, demonstrate a regular and strong dependence of anaerobic remineralization on diffusive transport. For example, net production of NH 4 + , HPO 4 = , I - , and Mn ++ increases as the effective distance between burrows becomes ≤2 cm (burrow abundance ≥800 m -2 ) in otherwise identical anoxic sediment. Corresponding changes in sedimentary bacterial numbers, exoenzyme activity, per cell growth rate (RNA), and solid phase properties (N, C/N, P) indicate that the increases in net rates are due in part to an absolute increase in total production. Transport-reaction models and experimental results demonstrate that relative decreases in the uptake of solutes into biomass, abiogenic precipitation reactions, and increased removal of inhibiting metabolites all occur simultaneously, enhancing both total and net remineralization. The phenonomenological first-order rate constant for organic matter decomposition is therefore a function not only of the reductant and oxidant pool properties, but also the environmental transport regime. Solid phase reaction products can differ substantially as a function of diffusive openness. For example, both organic P and the organic Plinorganic P ratio increase in more diffusively-open (irrigated) compared to diffusively-closed, anoxic sediment. The sensitivity of solute concentrations, microbial activity and diagenetic reaction balances to diffusive transport regime, indicates that macrofauna can functionally manipulate these properties through relatively small changes in burrow spacing patterns and individual burrow geometries.

Distribution and abundance of burrows formed by Lumbricus terrestris L. and Aporrectodea caliginosa Sav. in the soil profile

The distribution of burrows made by Lumbricus terrestris L. and Aporrectodea caliginosa Sav. was studied on an unploughed field. The positions of earthworm burrows were mapped in 9 horizontal planes to a depth of 80 cm in a pit of 70 by 40 cm. Burrow diameter and presence of plant roots growing in burrows were also recorded. Burrows on six of the nine planes were considered as two-dimensional point patterns and analyzed as spatial point processes. A three-dimensional image was constructed for burrows formed by L. terrestris. The total number of burrows ranged between 180 and 1260 m −2 at depths of 80 and 30 cm, respectively. The majority of burrows were evidently formed by A. caliginosa. The smallest size class (2–3 mm) of burrows was dominant at depths between 8 and 40 cm. Deeper in the soil profile, the proportion of larger burrows increased markedly. Burrows formed by L. terrestris appeared to be non-branching, and extended vertically beyond 80 cm. In all soil layers studied, burrow distribution was found to be completely random. The proportion of burrows containing plant roots was between 18 and 60%, at depths of 80 and 15 cm, respectively.

Ichnology of a reworked strandplain complex: Mississippian Hartselle Sandstone of Alabama

The Hartselle Sandstone of northern Alabama represents a mesotidal strandplain complex of Hombergian (middle Chesterian) age that was reworked by a transgressing sea. Transgressive reworking resulted in complex facies patterns that can best be deciphered by ichnology. Thickly bedded, unbioturbated beach to shoreface sandstone is widespread at the base of the formation. Wavy-bedded back-barrier to shelf sandstone and shale predominate in the middle and upper parts of the formation and contain distinctive assemblages of trace fossils, invertebrates, and plants.Barriers with a broad, gently sloping beach face and muddy coastal swamps typified the Hartselle strandplain which extended across northern Alabama. Barrier and coastal-swamp deposits lack trace fossils but locally contain an indigenous lycopod flora including stumps and Stigmaria root systems.Back-barrier tidal flats and lagoon deposits have trace-fossil assemblages dominated by bivalve traces that probably represent brackish environments. Marginal-marine sandstone contains chiefly monospecific assemblages and is reworked by bivalves and unknown organisms; Lockeia, Uchirites, and Rosselia are dominant at different sites. The Lockeia assemblage includes bedding surfaces with crowded bivalve resting traces. The abundance, density, and small size of monospecific burrows suggests estuarine conditions with high food supply and rapid larval colonization. The Uchirites assemblage is characterized by bivalve trails, representing probably brackish substrates with a high sedimentation rate.Shelf sandstone and shale include bivalve resting traces and trails (Lockeia ispp., Uchirites isp. aff. U. triangularis, Walcottia rugosa, and W. imbricata), asteroid and ophiuroid resting traces (Asteriacites stelliforme and Pentichnus pratti), trilobite resting traces and trackways (Rusophycus ispp. and Petalichnus isp.), and dwelling burrows, feeding burrows, trails, and trackways of unknown organisms (Chondrites-like burrows, Phycodes isp., Haplotichnus isp., Rosselia isp., Planolites montanus, Nereites missouriensis, Tasmanadia twelvetreesi, imbricate burrows, and wavelike burrows). Some shelf areas even supported diverse calcified faunas containing crinoids, fenestrate bryozoans, and articulate brachiopods.The Hartselle Sandstone is a facies mosaic that records indundation of an extensive strandplain complex and a distinctive stratigraphic succession of lithofacies and biofacies. Hartselle ichnofacies have unique aspects, but are similar to those of other marginal-marine Carboniferous strata in eastern North America. The paleoecologic complexity of the Hartselle Sandstone helps to establish the dynamic range of Carboniferous ecosystems, which have yet to be fully explored.

Paleoecologic aspects of ichnofabrics (biogenic sedimentary fabrics) in deep-sea sediment

The paleoecology of deep-sea, benthic, macroinvertebrate communities is largely confined to the trace fossil record. While a few taxa have preservable hard parts, most of the deep-sea macrofauna are unpreservable as body fossils below the aragonite or calcite compensation depths. The ichnologic record provides important synecologic information regarding the behavioral diversity and endobenthic habitat partitioning of at least some community members.The deep-sea trace fossil record is strongly influenced by sediment composition (biogenic calcite vs. terrigenous clay), sedimentation regime (pelagic vs. turbidite deposition) and bioturbation history (continuous vs. discontinuous burrowing). These influences are directly reflected in the ichnofabric, or biogenic sedimentary fabric.Ichnofabrics of deep-sea sediments can shed light on the ecologic relationships of the infaunal community (trophic and tiering relationships), occupation of the sea floor by successive and different communities (deciphered from the different trace fossil suites in a composite ichnofabric), stability and firmness of the sedimentary substrate (revealed by burrow distinctness and deformation), interstitial oxygen conditions below the sea floor (determined from the abundance and preservation state of deposit-feeding burrows, such as Chondrites and Zoophycos), and effects of bioturbation patterns on early diagenetic processes (differential cementation and mineralization).The sedimentary habitat of the ancient deep-sea floor changes through time via compaction, dewatering, cementation and secondary mineralization. The benthos that inhabit this changing habitat likewise change according to their differing requirements for burrowing and endobenthic feeding. The resulting ichnofabric reflects a successive occupation of the sea floor by different types of organisms, ranging from shallow burrowers to deep burrowers to hard-substrate borers. Composite ichnofabrics thus can reveal a complex sequence of ecologic and diagenetic events.The tiered structure of infaunal communities in late Cretaceous and early Tertiary shelf-sea chalks is well-known, and because of their pelagic depositional aspect, these situations provide good analogues in outcrop for truly deep-sea environments. In the European and North American chalks, deeply emplaced fodinichnia (Thalassinoides, Chondrites and Zoophycos) typically are superimposed upon shallowly emplaced fodinichnia and pascichnia (Planolites and Teichichnus). Tracks and trails of epifaunal animals certainly were produced at the sediment-water interface, but they are not preserved. Very similar ichnofabrics occur in late Cretaceous and early Tertiary pelagic carbonates in New Zealand, where composite ichnofabrics reveal at least five main phases of occupation of the substrate by burrowers and borers. Multiple generations of Thalassinoides include both burrows and borings, each produced at different stages in the development of a major regional unconformity.Deep-sea pelagic deposits (in kilometers of water) represent a continuous accretion of the sea floor during sediment accumulation, accompanied by a continuous vertical shift of a tiered endobenthic community of burrowers that does not change appreciably over short time intervals. In partial contrast, shelf-sea pelagic deposits (in hundreds of meters of water) are affected more directly by short-term changes in bathymetry, salinity and oxygenation. The response of benthic communities to environmental shifts at the sea floor, therefore, is more pronounced in shelf-sea than in deep-sea settings.

The status of the Red Hills salamander Phaeognathus hubrichti, Alabama, USA, 1976–1988

A total of 144 sites in the Red Hills Physiographic Province in south-central Alabama, USA, were surveyed in 1988 for burrows of the Red Hills salamander Phaeognathus hubrichti. Of 92 sites surveyed in 1976, no change occurred in the habitat at 54 sites, conditions improved at 19 sites and deteriorated at 18 sites following selective or clear cutting. An additional 14 of 52 sites not surveyed in 1976 were adversely affected by logging. Burrows were most often found on high (x̄ = 17 m), steep (x̄ = 50°), uncut slopes containing a high soil moisture content (x̄ = 57%) and full tree canopy. Slope angle and soil pH did not affect burrow abundance. Burrow openings averaged 10·9 mm high × 15·3 mm wide. Burrow angle was negatively correlated with burrow width and slope angle but low r2 values indicate that little of the variation was explained by these variables. Burrows were most often found on the upper two-thirds of slopes; burrows on slopes affected by cutting were found in the middle of the slope where they were less prone to disturbance and desiccation. Although most timber companies claim to no longer cut steep slopes in order to protect salamanders, detrimental forestry practices are still occuring. In some instances, Red Hills salamanders survive selective and clear cutting, but the persistence and viability of affected populations remain unknown. Suggestions are made to reduce impacts from forestry operations. Acquisition of 25 sites containing viable salamander populations and retention as a threatened species under United States federal law are recommended.

The distribution and abundance of Helice tridens (De Haan) burrows and substratum conditions in a northeastern Japan salt marsh (Crustacea: Brachyura)

The effects of the physical condition of the substratum on the distribution and abundance of mud-crab burrows were investigated. In the salt-marsh habitats studied, where burrows were abundant, there was a high proportion of silt-clay. In such conditions, the diameters of openings and the depths of the burrows were greater than those when the relative proportion of silt-clay was low. In the laboratory, it was found that with a low proportion of clay, mud-crabs did not dig burrows when the water content was high and thus equivalent to that in the marsh. When the proportion of silt-clay was low, the larger mud-crabs did not make burrows at the depth of the water table in the marsh, because the layer above the water table was too thin to allow construction of the burrow. The field observations could thus be explained by the results of experiments showing that the depth of the burrows was controlled by the depth of the water table and the relative proportion of silt-clay in the substratum.

Estimation of Habitat Quality and Summer Population Density for Muskrats on a Watershed Basis

A model for assessing habitat quality for muskrats (Ondatra zibethicus) was field tested in central Massachusetts during 1978-79 and in northcentral Pennsylvania during 1981-82. The habitat model predicted favorable habitat and ranked watersheds with respect to potential muskrat abundance using topographic maps. Local population attributes must be combined with habitat analyses to obtain reliable quantitative estimates of muskrat numbers. Summer density estimates of 23 muskrats/km and 48 muskrats/km were obtained for an unglaciated and a glaciated river, respectively. J. WILDL. MANAGE. 50(2):269-273 To fill the need for an economically feasible method of inventorying riverine muskrats, we developed a multivariate model of habitat selection based on principal components regression (PCR) with data from 5 watersheds in Massachusetts (Brooks 1980, Brooks and Dodge 1981, Allen and Hoffman 1984). When applied to 3 additional rivers in Massachusetts this model successfully identified favorable muskrat habitat. However, when quantitative predictions from the model were compared to actual censuses, the numbers of burrows were underestimated ( +? SE = 55 ? 4%, range = 32-71%). A curvilinear equation was developed to correct for this underestimation (Brooks and Dodge 1981). The importance of validating habitat models before implementation has been discussed by many authors (see Lancia et al. 1982). Therefore, the objective of this study was to determine the reliability of the corrected habitat model for qualitative assessments of muskrat habitat and quantitative estimates of muskrat abundance. Appreciation is extended to L. Bors-Koefoed for his assistance in the field and to S. D. Miller, J. M. Payne, D. R. Progulske, A. J. Steiner, and R. H. Yahner for earlier reviews of the manuscript. This study was cooperatively supported by the Mass. Coop. Wildl. Res. Unit (U.S. Fish and Wildl. Serv., Mass. Div. Fish. and Wildl., Univ. Massachusetts, Amherst, and Wildl. Manage. Inst.), Pennsylvania State Univ. (DuBois Campus and School For. Resour.), and SigmaXi. This is J. Ser. 6963 of the Pa. Agric. Exp. Stn. STUDY AREA AND METHODS The habitat model was developed on data collected on 8 watersheds in Massachusetts (Brooks 1980). The main study area, the Ware River, is in the central plateau region and flows southwest about 90 km through upland forests and wooded wetlands, agricultural land and pasture, and mill towns into the Connecticut River Basin. Fifty 300-m sections were selected randomly on the Ware River from May to October 1978 for study. Supplemental data were collected from 24 sections that were chosen randomly on 4 other rivers during July-August 1979: the Quaboag and Chicopee rivers of the Chicopee Basin, the Manhan of the Connecticut River Basin, and the Nashua which flows north to the Merrimack River Basin. A model of habitat selection by muskrats was developed from data collected on these 5 rivers. To refine the predictive capability of the habitat model, we studied 16 sections on 3 additional rivers in September 1979: the north-flowing ConcordAssabet system of the Merrimack River Basin and the Massachusetts portion of the southflowing Housatonic River (Brooks and Dodge 1981). The adjusted habitat model was tested on data from Sandy Lick Creek in northcentral Pennsylvania during the summers of 1981 and 1982. Sandy Lick Creek flows 48 km from the eastern continental divide west to the Ohio River Basin. Information on hydrology, soils, vegetation, land use, bank structure and composition, burrow and house abundance, and muskrat signs was