Does electric fishing influence movements of fishes in streams? Experiments with brook trout, Salvelinus fontinalis
[No abstract available]
Fisheries Management and Ecology↗
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Spatial capture-recapture models allowing Markovian transience or dispersal
Spatial capture–recapture (SCR) models are a relatively recent development in quantitative ecology, and they are becoming widely used to model density in studies of animal populations using camera traps, DNA sampling and other methods which produce spatially explicit individual encounter information. One of the core assumptions of SCR models is that individuals possess home ranges that are spatially stationary during the sampling period. For many species, this assumption is unlikely to be met and, even for species that are typically territorial, individuals may disperse or exhibit transience at some life stages. In this paper we first conduct a simulation study to evaluate the robustness of estimators of density under ordinary SCR models when dispersal or transience is present in the population. Then, using both simulated and real data, we demonstrate that such models can easily be described in the BUGS language providing a practical framework for their analysis, which allows us to evaluate movement dynamics of species using capture–recapture data. We find that while estimators of density are extremely robust, even to pathological levels of movement (e.g., complete transience), the estimator of the spatial scale parameter of the encounter probability model is confounded with the dispersal/transience scale parameter. Thus, use of ordinary SCR models to make inferences about density is feasible, but interpretation of SCR model parameters in relation to movement should be avoided. Instead, when movement dynamics are of interest, such dynamics should be parameterized explicitly in the model.
Population Ecology↗
Molecular detection of hematozoa infections in tundra swans relative to migration patterns and ecological conditions at breeding grounds
Tundra swans ( Cygnus columbianus ) are broadly distributed in North America, use a wide variety of habitats, and exhibit diverse migration strategies. We investigated patterns of hematozoa infection in three populations of tundra swans that breed in Alaska using satellite tracking to infer host movement and molecular techniques to assess the prevalence and genetic diversity of parasites. We evaluated whether migratory patterns and environmental conditions at breeding areas explain the prevalence of blood parasites in migratory birds by contrasting the fit of competing models formulated in an occupancy modeling framework and calculating the detection probability of the top model using Akaike Information Criterion (AIC). We described genetic diversity of blood parasites in each population of swans by calculating the number of unique parasite haplotypes observed. Blood parasite infection was significantly different between populations of Alaska tundra swans, with the highest estimated prevalence occurring among birds occupying breeding areas with lower mean daily wind speeds and higher daily summer temperatures. Models including covariates of wind speed and temperature during summer months at breeding grounds better predicted hematozoa prevalence than those that included annual migration distance or duration. Genetic diversity of blood parasites in populations of tundra swans appeared to be relative to hematozoa prevalence. Our results suggest ecological conditions at breeding grounds may explain differences of hematozoa infection among populations of tundra swans that breed in Alaska.
Alaska↗
Spatiotemporal patterns in habitat use of natal and non-natal adult Atlantic sturgeon in two spawning rivers
Background Monitoring movement across an organism’s ontogeny is often challenging, particularly for long-lived or wide-ranging species. When empirical data are unavailable, general knowledge about species’ ecology may be used to make assumptions about habitat use across space or time. However, inferences about habitat use based on population-level ecology may overlook important eco-evolutionary contributions from individuals with heterogenous ethologies and could diminish the efficacy of conservation and management. Methods We analyzed over a decade of acoustic telemetry data to understand individual differences in habitat use of federally endangered adult Atlantic sturgeon ( Acipenser o. oxyrinchus ) in the Delaware and Hudson rivers during spawning season. In particular, we sought to understand whether sex or natal origin could predict patterns in habitat use, as there is a long-held assumption that adult Atlantic sturgeon seldom stray into non-natal rivers. Results In both rivers, migration timing, spawning habitat occupancy, and maximum upstream migration distance were similar between natal and non-natal individuals. While non-natal individuals represented only 13% of fish detected in the Hudson River, nearly half of all tagged fish detected in the Delaware River were non-natal and generally occupied freshwater habitats longer than natal individuals. In both systems males had more heterogenous patterns of habitat use and longer duration of occupancy than did females. Conclusions This study demonstrates the importance of non-natal rivers for fulfilling ontogenetic habitat requirements in Atlantic sturgeon. Our results may also highlight an opportunity to improve conservation and management by extending habitat designations to account for more heterogenous patterns in individual habitat use in non-natal freshwater environments.
Delaware↗
Applying circuit theory and landscape linkage maps to reintroduction planning for California condors
Conservation practitioners are increasingly looking to species translocations as a tool to recover imperiled taxa. Quantitative predictions of where animals are likely to move when released into new areas would allow managers to better address the social, institutional, and ecological dimensions of conservation translocations. Using >5 million California condor ( Gymnogyps californianus ) occurrence locations from 75 individuals, we developed and tested circuit-based models to predict condor movement away from release sites. We found that circuit-based models of electrical current were well calibrated to the distribution of condor movement data in southern and central California (continuous Boyce Index = 0.86 and 0.98, respectively). Model calibration was improved in southern California when additional nodes were added to the circuit to account for nesting and feeding areas, where condor movement densities were higher (continuous Boyce Index = 0.95). Circuit-based projections of electrical current around a proposed release site in northern California comported with the condor’s historical distribution and revealed that, initially, condor movements would likely be most concentrated in northwestern California and southwest Oregon. Landscape linkage maps, which incorporate information on landscape resistance, complement circuit-based models and aid in the identification of specific avenues for population connectivity or areas where movement between populations may be constrained. We found landscape linkages in the Coast Range and the Sierra Nevada provided the most connectivity to a proposed reintroduction site in northern California. Our methods are applicable to conservation translocations for other species and are flexible, allowing researchers to develop multiple competing hypotheses when there are uncertainties about landscape or social attractants, or uncertainties in the landscape conductance surface.
Central California↗
Evaluating the institutional and ecological effects of invasive species prevention policy: A case study from the U.S. Fish and Wildlife Service
Wildlife and natural resource institutions play key roles in invasive species monitoring and management. Paradoxically, the extensive fieldwork undertaken by these institutions and their partners may result in the inadvertent movement and spread of invasive species within and between sensitive ecosystems. In this work, we consider the potential effects of internal guidelines and policies designed to prevent the spread of invasive species by the field activities of management institutions and their partners. Such policies could be high-leverage tools for invasive species prevention, however, as large, complex organizations seek to implement policies to limit the spread of invasive species, it may be challenging to accommodate the wide diversity of potential invasion pathways and mitigation efforts facilitated via the programs, activities, and ecosystems they manage. Prevention policies may also be met with resistance due to the costs of implementation unless concrete benefits can be demonstrated. Assessing and communicating the effects of prevention policies could motivate improved implementation and adherence by institutional units and partners and could help inform adaptive policy changes. However, assessing the effectiveness of invasive species prevention presents a unique set of challenges, including incomplete data on invasive species distribution and pathways, that make it difficult to measure the effects of prevention efforts. In this work, we present a conceptual framework for evaluating institutional policies for invasive species prevention. We describe a flexible, multifaceted approach that considers policy implementation and adherence as well as ecological outcomes. We discuss potential application of this framework using a policy recently implemented by the Pacific Region of the U.S. Fish and Wildlife Service to prevent the introduction and spread of invasive species by service personnel and partners during field activities as a case study.
Management of Biological Invasions↗
Divergent movements of walrus and sea ice in the northern Bering Sea
The Pacific walrus Odobenus rosmarus divergens is a large Arctic pinniped of the Chukchi and Bering Seas. Reductions of sea ice projected to occur in the Arctic by mid-century raise concerns for conservation of the Pacific walrus. To understand the significance of sea ice loss to the viability of walruses, it would be useful to better understand the spatial associations between the movements of sea ice and walruses. We investigated whether local-scale (~1 to 100 km) walrus movements correspond to movements of sea ice in the Bering Sea in early spring, using locations from radio-tracked walruses and measures of ice floe movements from processed synthetic aperture radar satellite imagery. We used generalized linear mixed-effects models to analyze the angle between walrus and ice floe movement vectors and the distance between the final geographic position of walruses and their associated ice floes (displacement), as functions of observation duration, proportion of time the walrus was in water, and geographic region. Analyses were based on 121 walrus-ice vector pairs and observations lasting 12 to 36 h. Angles and displacements increased with observation duration, proportion of time the walrus spent in the water, and varied among regions (regional mean angles ranged from 40° to 81° and mean displacements ranged from 15 to 35 km). Our results indicated a lack of correspondence between walruses and their initially associated ice floes, suggesting that local areas of walrus activities were independent of the movement of ice floes.
Marine Ecology Progress Series↗
Space use and site fidelity of wintering whooping cranes on the Texas Gulf Coast
The Aransas-Wood Buffalo population (the only non-reintroduced, migratory population) of endangered whooping cranes ( Grus americana ) overwinters along the Texas Gulf Coast, USA. Understanding whooping crane space use on the wintering grounds reveals essential aspects of this species' ecology, which subsequently assists with conservation. Using global positioning system telemetry data from marked whooping cranes during 2009–2017, we fit continuous-time stochastic process models to describe movement and home range using autocorrelated kernel density estimation (AKDE) and explored variation in home range size in relation to age, sex, reproductive status, and drought conditions. We used the Bhattacharyya coefficient of overlap and distance between home range centroids to quantify site fidelity. We examined the effects of time between winter home ranges and the sex of the crane on site fidelity using Bayesian mixed-effects beta regression. Winter whooping crane 95% AKDE home range size averaged 30.1 ± 45.2 (SD) km 2 (median = 14.3, range = 1.1–308.6). Home ranges of sub-adult females were approximately 2 times larger than those of sub-adult males or families. As drought worsened, home ranges typically expanded. Between consecutive years, the home ranges of an adult crane exhibited 68 ± 31% overlap (site fidelity), but fidelity to winter sites declined in subsequent winters. The overlap of adult home ranges with the nearest unrelated family averaged 33 ± 28%. As a whooping crane aged, overlap with its winter home range as a juvenile declined, regardless of sex. By 4 years of age, a whooping crane had approximately 14 ± 28% overlap with its juvenile winter home range. Limited evidence suggested male whooping cranes return to within 2 km of their juvenile home range by their fifth winter. Previous data obtained from aerial surveys led ecologists to assume that whooping crane families normally used small areas (~2 km 2 ) and expressed persistent site fidelity. Our analyses showed <8% of families had home ranges ≤2 km 2 , with the average area 15 times greater, and waning site fidelity over time. Our work represents an analysis of whooping crane home ranges for this population, identifying past misconceptions of winter space use and resulting in better estimates of space requirements for future conservation efforts.
Texas↗
Interisland genetic structure of two endangered Hawaiian waterbirds: The Hawaiian Coot and Hawaiian Gallinule
Most of Hawaii's endemic avifauna are species of conservation concern. Some of Hawaii's endangered waterbirds, however, have increased in number as a result of intensive management of wetlands. To inform these conservation efforts, we examined interisland genetic structure and gene flow within 2 Hawaiian endemic waterbirds, the Hawaiian Coot ( Fulica alai ) and the Hawaiian subspecies of the Common Gallinule ( Gallinula galeata sandvicensis ), using microsatellite and mitochondrial loci. Hawaiian Coots and Hawaiian Gallinules occupy coastal wetlands and exhibit similar life history characteristics and generation times, although they may differ in dispersal propensity. Mark–resight data for Hawaiian Coot indicate interisland movements, whereas Hawaiian Gallinules are sedentary. Genetic diversity is partitioned across the landscape differently for Hawaiian Coots and Hawaiian Gallinules; patterns of variation are likely influenced by behavioral and ecological mechanisms. Hawaiian Coots exhibit low levels of structure at microsatellite loci ( F ST = 0.029) and high levels of gene flow among islands. Conversely, Hawaiian Gallinules are highly structured across marker types (microsatellite F ST = 0.205, mtDNA control region F ST = 0.370, mtDNA ND2 F ST = 0.087), with restricted recent gene flow. Patterns of gene flow have changed after the population declines in the early to mid-1900s. Gene flow estimates indicate historical dispersal from Kauai to Oahu in both species, while recent estimates show individual Hawaiian Coots dispersing from Oahu and restricted gene flow between islands for the Hawaiian Gallinule. Changes in gene flow through time suggest that patterns of dispersal may be an artifact of the availability of habitat, which may be indirectly associated with the synergistic influences of population density and wetland quality. Despite recent population size increases for both species, continued threats to Hawaiian waterbirds (i.e. nonnative mammalian predators and invasive plants, avian disease, altered hydrology, and saltwater inundation of freshwater wetlands) will likely require continued active management to maintain viable populations.
Hawaii↗
Shallow Groundwater Movement in the Skagit River Delta Area, Skagit County, Washington
Shallow groundwater movement in an area between the lower Skagit River and Puget Sound was characterized by the U.S. Geological Survey to assist Skagit County and the Washington State Department of Ecology with the identification of areas where water withdrawals from existing and new wells could adversely affect streamflow in the Skagit River. The shallow groundwater system consists of alluvial, lahar runout, and recessional outwash deposits composed of sand, gravel, and cobbles, with minor lenses of silt and clay. Upland areas are underlain by glacial till and outwash deposits that show evidence of terrestrial and shallow marine depositional environments. Bedrock exposures are limited to a few upland outcrops in the southwestern part of the study area, and consist of metamorphic, sedimentary, and igneous rocks. Water levels were measured in 47 wells on a quarterly basis (August 2007, November 2007, February 2008, and May 2008). Measurements from 34 wells completed in the shallow groundwater system were used to construct groundwater-level and flow-direction maps and perform a linear-regression analysis to estimate the overall, time averaged shallow groundwater-flow direction and gradient. Groundwater flow in the shallow groundwater system generally moves in a southwestward direction away from the Skagit River and toward the Swinomish Channel and Skagit Bay. Local groundwater flow towards the river was inferred during February 2008 in areas west and southwest of Mount Vernon. Water-level altitudes varied seasonally, however, and generally ranged from less than 3 feet (August 2007) in the west to about 15 feet (May 2008) in the east. The time-averaged, shallow groundwater-flow direction derived from regression analysis, 8.5 deg south of west, was similar to flow directions depicted on the quarterly water-level maps. Seasonal changes in groundwater levels in most wells in the Skagit River Delta follow a typical pattern for shallow wells in western Washington. Water levels rise from October through March, when precipitation is high, and decline from April through September, when precipitation is lower. Groundwater levels in wells along the eastern margin of the study area also are likely influenced by stage on the Skagit River. Water levels in these wells remained elevated through April, and did not seem to begin to decline until the end of May in response to declining river stage. Groundwater levels in a well equipped with a continuous water-level recorder exhibited periodic fluctuations that are characteristic of ocean tides. This well is less than 1 mile east of the tidally influenced Swinomish Channel, and exhibited water-level fluctuations that correspond closely to predicted tidal extremes obtained from a tide gage near La Conner, Washington.
Scientific Investigations Report↗
Sexual differentiation in the distribution potential of northern jaguars ( Panthera onca )
We estimated the potential geographic distribution of jaguars in the southwestern United States and northwestern Mexico by modeling the jaguar ecological niche from occurrence records. We modeled separately the distribution of males and females, assuming records of females probably represented established home ranges while male records likely included dispersal movements. The predicted distribution for males was larger than that for females. Eastern Sonora appeared capable for supporting male and female jaguars with potential range expansion into southeastern Arizona. New Mexico and Chihuahua contained environmental characteristics primarily limited to the male niche and thus may be areas into which males occasionally disperse.
Arizona;Chihuahua;New Mexico;Sonora;Texas↗
Diel horizontal migration in streams: juvenile fish exploit spatial heterogeneity in thermal and trophic resources
Vertical heterogeneity in the physical characteristics of lakes and oceans is ecologically salient and exploited by a wide range of taxa through diel vertical migration to enhance their growth and survival. Whether analogous behaviors exploit horizontal habitat heterogeneity in streams is largely unknown. We investigated fish movement behavior at daily timescales to explore how individuals integrated across spatial variation in food abundance and water temperature. Juvenile coho salmon made feeding forays into cold habitats with abundant food, and then moved long distances (350–1300 m) to warmer habitats that accelerated their metabolism and increased their assimilative capacity. This behavioral thermoregulation enabled fish to mitigate trade-offs between trophic and thermal resources by exploiting thermal heterogeneity. Fish that exploited thermal heterogeneity grew at substantially faster rates than did individuals that assumed other behaviors. Our results provide empirical support for the importance of thermal diversity in lotic systems, and emphasize the importance of considering interactions between animal behavior and habitat heterogeneity when managing and restoring ecosystems.
Alaska↗
Satellite tracking reveals heavy use of local MPAs by green turtles (Chelonia mydas) nesting in southeast Florida, USA
Florida hosts a regionally important nesting aggregation of green turtles ( Chelonia mydas ) in the North Atlantic, yet internesting and post-nesting movements for this rookery remain poorly understood. Here, we used satellite telemetry to track 23 green turtles nesting on southeast Florida beaches from 2017 to 2021 to investigate their spatial ecology and use of marine protected areas (MPAs) during internesting, migration, and foraging. Marine protected areas are widely used in marine conservation and can be powerful tools for managing species and protecting biodiversity. During internesting, turtles used nearshore, unprotected coastal waters adjacent to the study site. After the nesting season, turtles migrated 24.1 to 203.5 km to previously identified foraging grounds, including areas within Biscayne National Park and Florida Keys National Marine Sanctuary, as well as a high-use but unprotected area off Cape Sable, Florida. Throughout the internesting and foraging periods, turtles exhibited little spatial overlap of core-use areas, suggesting limited space-use sharing even in high-density regions. This study provides the first satellite telemetry dataset for green turtles from southeast Florida and reveals their strong reliance on a relatively small MPA network along southwest Florida. Our findings underscore how these MPAs can support conservation efforts for Florida’s overall green turtle nesting population, while further emphasizing the potential benefits of expanded protections in key areas to safeguard regionally important green turtle habitat.
Florida↗
Translocations as a tool for restoring populations of bighorn sheep
We analyzed factors that contributed to the success of 100 translocations of bighorn sheep within six western states between 1923 and 1997. We categorized the populations as unsuccessful (i.e., extirpated or remnant, <29 animals), moderately successful (30–99 animals), and successful (100–350 animals) by the end of the study period in 1997. Thirty of the translocated populations were unsuccessful ( n = 13 were extirpated and n = 17 were remnant), 29 were moderately successful, and 41 were successful (21 ± 1.3 [SE] years of information per translocation). Translocations were less successful when domestic sheep were located within 6 km of the known bighorn sheep use areas (logistic regression, p = 0.052). Grazing of cattle on the same range also negatively influenced success ( p = 0.004). Use of indigenous versus previously translocated source stocks increased success ( p = 0.084). The translocation was twice as likely to be successful when indigenous herds were used as sources ( p = 0.043), but mixing genetic stocks ( p = 0.381) or later additional augmentations did not influence success ( p = 0.095). Annual migrations by newly established translocated populations increased success ( p = 0.014). We recommend translocations of founder groups of bighorn sheep from indigenous sources into large patches of habitat that promote movements and migrations, and with no domestic sheep present in the area.
Restoration Ecology↗
Coarse-scale movement patterns of a small-bodied fish inhabiting a desert stream
Located on the floor of Death Valley (CA, USA), Salt Creek harbors a single fish species, the Salt Creek pupfish, Cyprinodon salinus salinus, which has adapted to this extremely harsh environment. Salt Creek is fed by an underground spring and is comprised of numerous pools, runs, and marshes that exhibit substantial variability in temperature, salinity, and dissolved oxygen concentrations. In addition, the wetted area of Salt Creek is reduced throughout the summer months due to high rates of evaporation, with some reaches drying completely. Therefore, it seems logical that short- and long-term movement patterns may play an important role in Salt Creek pupfish population dynamics. The objective of this study was to describe coarse-scale movements of Salt Creek pupfish in Salt Creek during their breeding season from March to May. Sex ratios and length–frequency distributions varied spatially within Salt Creek, suggesting population segregation during the breeding season. Long-distance movements were generally rare, although two fish moved more than 1.2 km. Movement in upstream reaches was rare or absent, in contrast to the greater movement observed in downstream reaches (29% of recaptures). Temporal trends and demographic patterns in movement were not observed. Because the two most downstream habitats dry up in the summer, our results indicate that coarse-scale movements that re-populate downstream reaches likely occur during other times of year. Consequently, the importance of small- and large-scale movements is influenced by season. Further assessment of Salt Creek movement patterns conducted during other times of year may better illuminate long-distance movement patterns and source-sink dynamics.
California↗
Animal movement models for migratory individuals and groups
Animals often exhibit changes in their behaviour during migration. Telemetry data provide a way to observe geographic position of animals over time, but not necessarily changes in the dynamics of the movement process. Continuous‐time models allow for statistical predictions of the trajectory in the presence of measurement error and during periods when the telemetry device did not record the animal's position. However, continuous‐time models capable of mimicking realistic trajectories with sufficient detail are computationally challenging to fit to large datasets. Furthermore, basic continuous‐time model specifications (e.g. Brownian motion) lack realism in their ability to capture nonstationary dynamics. We present a unified class of animal movement models that are computationally efficient and provide a suite of approaches for accommodating nonstationarity in continuous trajectories due to migration and interactions among individuals. Our approach uses process convolutions to allow for flexibility in the movement process while facilitating implementation and incorporating location uncertainty. We show how to nest convolution models to incorporate interactions among migrating individuals to account for nonstationarity and provide inference about dynamic migratory networks. We demonstrate these approaches in two case studies involving migratory birds. Specifically, we used process convolution models with temporal deformation to account for heterogeneity in individual greater white‐fronted goose migrations in Europe and Iceland, and we used nested process convolutions to model dynamic migratory networks in sandhill cranes in North America. The approach we present accounts for various forms of temporal heterogeneity in animal movement and is not limited to migratory applications. Furthermore, our models rely on well‐established principles for modelling‐dependent data and leverage modern approaches for modelling dynamic networks to help explain animal movement and social interaction.
Methods in Ecology and Evolution↗
Mountain Lions of the Flagstaff Uplands: 2003-2006 Progress Report
Executive Summary Stakeholders in management of mountain lions in the Flagstaff Uplands of northern Arizona have expressed increasing concern about both potential impacts of humans on lions and potential risks posed by lions to humans. A series of human-mountain lion encounters during 2000-2001 on Mt. Elden, immediately adjacent to Flagstaff, and similar incidents during 2004 near Tucson brought increased attention to management of human safety in mountain lion range. These human-centered concerns, together with long-standing questions about how the human infrastructure centered on Flagstaff might be affecting lion movements led us to initiate a mountain lion study in 2003 which we plan to continue through 2009. Our study focuses on movements and other behaviors of mountain lions, with the goal of providing information that can be used to increase human safety, decrease human impacts, and, overall, provide insight into the ecology of lions in this region. To serve this goal, we have focused on collecting data that will be the basis of explanatory models that can provide spatially-explicit predictions of mountain lion activity, specify the effects of human facilities, such as highways and urban areas, and provide insight into when, where, and how often different kinds of lions kill different kinds of prey. During 2003-2006, we captured six female and five male mountain lions in the Flagstaff Uplands, 10 of which we fitted with collars that collected up to six high-precision GPS fixes per day, transmitted daily to our offices via Argos satellites. This timely delivery of data allowed us to visit kill sites and other foci of localized activity to collect detailed information on lion behavior. By June 2006 we had obtained 9357 GPS locations and visited 394 sites, at which we documented 218 kills, 165 of which were by five females and 53 by five males. These data were the basis for preliminary analyses presented in this report. All lions during all seasons exhibited a strong selection for rough terrain and forest or woodland cover. Females differed from males by selecting more strongly for intermediate, rather than extreme, levels of terrain roughness, by selecting more strongly for chaparral vegetation and related rocky areas during winter, and by not selecting as strongly for areas near water sources. Overall, lions collared during this study strongly avoided flat open areas in private ownership. Male but not female lions exhibited pronounced selection for National Park Service jurisdictions. Both males and females year-round avoided residential areas and a zone outward to about 1-3 km and, when within this zone, moved more slowly and with less change in direction compared to when farther away. Collared lions have so far rarely crossed paved highways of any description - orders of magnitude less often than expected by chance. We observed only 3 crossings of an interstate highway, all on I17 and none on I40. Elk comprised the majority (52%) of kills by lions in our study, followed by mule deer (46%), and small mammals (15%). Adults comprised most of the mule deer kills (68%) and mesocarnivores, primarily coyotes (n = 21), comprised 73% of smaller prey. Calf and short-yearling elk comprised the largest single category of kills (29%). In addition to kills, we documented seven instances of scavenging, involving four different lions. Females differed from males by killing more mule deer and virtually all of the mesocarnivores, and by killing fewer elk of all ages. Intervals between kills averaged between 144 hrs (young females) to 221 hours (adult females), whereas average time spent on a kill ranged from 19 hrs (adult males) to 40 hrs (young males). Carcass mass had a strong effect on likelihood that a lion would bury or relocate a kill, the percentage of edibles consumed, and overall time spent feeding. Time spent feeding and likelihoods of carcass burial and relocation all peaked at intermediate carcass masses, suggesting an optimal mass in the range of 50-150 kg, likely dictated as much by handling efficiencies and competition from other scavengers as by a lion's shear ability to kill prey. Adult male lions exhibited a life strategy distinctly different from all other sex-age classes that entailed moving more rapidly over larger areas, and spending less time on kills in which they invested less energy handling, but from which they consumed tissue at a higher sustained rate.
Open-File Report↗
Rangeland health attributes and indicators for qualitative assessment
Panels of experts from the Society for Range Management and the National Research Council proposed that status of rangeland ecosystems could be ascertained by evaluating an ecological site's potential to conserve soil resources and by a series of indicators for ecosystem processes and site stability. Using these recommendations as a starting point, we developed a rapid, qualitative method for assessing a moment-in-time status of rangelands. Evaluators rate 17 indicators to assess 3 ecosystem attributes (soil and site stability, hydrologic function, and biotic integrity) for a given location. Indicators include rills, water flow patterns, pedestals and terracettes, bare ground, gullies, wind scour and depositional areas, litter movement, soil resistance to erosion, soil surface loss or degradation, plant composition relative to infiltration, soil compaction, plant functional/structural groups, plant mortality, litter amount, annual production, invasive plants, and reproductive capability. In this paper, we detail the development and evolution of the technique and introduce a modified ecological reference worksheet that documents the expected presence and amount of each indicator on the ecological site. In addition, we review the intended applications for this technique and clarify the differences between assessment and monitoring that lead us to recommend this technique be used for moment-in-time assessments and not be used for temporal monitoring of rangeland status. Lastly, we propose a mechanism for adapting and modifying this technique to reflect improvements in understanding of ecosystem processes. We support the need for quantitative measures for monitoring rangeland health and propose some measures that we believe may address some of the 17 indicators.
Journal of Range Management↗