55121972
Inferred Spatial use by Elephants is Robust to Landscape Effects on GPS Telemetry
Global Positioning System (GPS) telemetry provides data to study spatial utilization patterns of animals. Spatial uncertainty due to poor accuracy and fix rates, however, may detract from inferences based on such data. The exclusion of two-dimensional (2D) locations may improve such inferences, but the prevalence of 2D locations may be a factor of landscape properties. In trials conducted using GPS units stationed at known positions, fix rate decreased significantly with increased canopy cover, but was unaffected by slope. Most (75%) of the locations recorded in closed woodland were 2D locations, suggesting that the exclusion of 2D locations may reduce estimates of the utilization of such habitats. Excluding 2D locations from records obtained for GPS units deployed on free-ranging elephants (Loxodonta africana) increased daily displacement distances, and changed the number of locations per habitat. However, selection ratios and estimates of home range area were not influenced by filtering location data. We concluded that although the exclusion of 2D locations improved the accuracy of locations per se, it resulted in significant data loss. This loss could alter inferences on patterns of spatial utilization.
83963636
Effects of habitat on GPS collar performance: using data screening to reduce location error
Summary 
 
1 
Global positioning system (GPS) technology enables researchers to evaluate wildlife movements, space use and resource selection in detail for extended periods of time. Two types of errors, missed location fixes and location error, are inherent to GPS telemetry and can bias location data sets. Habitat characteristics can influence both types of errors, but no studies have reported how continuous ranges of canopy cover and terrain simultaneously affect location error at different positional dilution of precision (PDOP) and signal quality levels. This information can assist in developing a protocol for removing large location errors from GPS data sets. 
 
2 
The objectives of this study were to quantify how canopy cover and terrain affected GPS collar performance within a mountainous region of northern Idaho, USA, and evaluate different data-screening options for GPS location data sets from stationary test collars and free-ranging black bears Ursus americanus. 
 
3 
The fix rate for test collars was very high in all habitats (mean 99·5%, SE 0·14, range 97·9–100%) and was not related to canopy cover or terrain obstruction. However, habitat variables strongly influenced location error, PDOP values and proportion of three-dimensional (3-D) fixes. The 95% circular error probable (CEP) equalled 106·8 m for locations at all test sites, and varied substantially with canopy cover, terrain obstruction and signal quality categories, ranging from 14·3 m to 557·0 m. Location errors for two-dimensional (2-D) fixes were more variable at higher PDOP values and were significantly larger compared with 3-D fixes. 
 
4 
Data screening increased the accuracy of test collar location data sets by removing large location errors that were associated with high PDOP values. Data-screening options that focused on screening 2-D locations were most effective in reducing location error and retaining the greatest number of locations. For black bear data sets, the four data screening options resulted in data reduction ranging from 8% to 35%. 
 
5 
Synthesis and applications. We have demonstrated how location data can be analysed and screened based on 2-D and 3-D fixes in relation to PDOP values to eliminate locations with potentially large location errors. This information can be applied to GPS location data for individual animals to increase data accuracy for analyses.
87341826
Effects of moose movement and habitat use on GPS collar performance
We tested a radiotelemetry collar that uses a Global Positioning System (GPS) unit to calculate animal locations. We placed the collar in a range of cover types and compared locations reported by the collar to differentially-corrected GPS locations. We placed the collar on a free-ranging moose (Alces alces) and determined how selection of cover types, collar movement, and collar orientation affected GPS locations. On or off the moose, the GPS unit collected a location in >90% of location attempts in areas with no or thin canopy cover, including mature deciduous canopies in winter. Under a mature conifer canopy or a mature deciduous canopy in summer, 60 to 70% of location attempts were successful. Locations from the GPS unit in the collar were close to the expected precision of non-differentially corrected GPS (within 40 m 50% of the time and 100 m 95% of the time). Locations did not have a directional bias. Movement of the moose while a location was being attempted did not affect GPS locations. The moose occasionally laid down so the collar was horizontal. Although this decreased the success of location attempts, <1% of location attempts were so affected. GPS radiotelemetry has great promise for expanding our knowledge about hourly, daily, and annual patterns in animal movements and habitat selection.
83940730
Accuracy of GPS telemetry collar locations with differential correction
Global Positioning System (GPS) units in telemetry collars provide an unbiased and precise estimate of animal locations. Under ideal conditions at least 50% of locations are expected to be within 40 m in uncorrected mode GPS, and within 5 m in differential mode GPS. When the collar was placed under open sky, most locations were 3-dimensional locations that could be differentially corrected. Under hardwood canopies with leaves on, the frequency of 3-dimensional locations decreased, the frequencies of failed location attempts and 2-dimensional locations increased, and the precision of GPS locations decreased. We compared the precision of each GPS mode by calculating uncorrected mode and differential mode locations from the same pseudo-range and ephemeris data. We varied the number of satellites used in the location solution to simulate the effect of decreased satellite acquisition due to canopy cover on precision of locations. Precision of locations increased if signals from >4 satellites were used to calculate the location in uncorrected mode and in differential mode. We found that 2-dimensional locations were almost as precise as 3-dimensional positions if the altitude of the GPS unit was known. If the altitude used to calculate a 2-dimensional location was within 50 m of the actual collar altitude, the precision of 2-dimensional differential mode locations was better than 3-dimensional uncorrected mode locations. If the error in altitude was 100 or 150 m, then 50% of 2-dimensional differential mode locations were within 70 m and 95% were within 185 m of the true location. We used GPS locations from collars placed in different cover types and on free-ranging moose (Alces alces) to determine the effect of season, time of day, rainfall, and cover type on GPS performance. On free-ranging moose the collar GPS unit found ≥4 satellites on 52% of location attempts, >50% of locations were 3-dimensional, and >24% of locations were 2-dimensional. Precise tracking of individual animals in all weather throughout the year is possible with GPS telemetry.
86870223
Field test of a GPS location system for moose Alces alces under Scandinavian boreal conditions
This paper reports on field tests of an animal-borne GPS telemetry system for moose Alces alces in northern Sweden. Tests involved accuracy of locations (standard mode GPS), percentage of successful location attempts under different canopy conditions, effect of movement, and performance of the GPS telemetry system on free-ranging moose. Locational accuracy was better than 92 and 183 m 95% of the time, and better than 42 and 74 m 50% of the time, respectively, dependent on whether the GPS receiver recorded a 2- or 3-dimensional location (3 or 4 satellites used to calculate the location). Percentage of successful location attempts ranged within 69–100%, and varied inversely with over-storey canopy cover and basal area of stems. Thick canopy cover and high stem basal area reduced locational accuracy and the percentage of successful location attempts. A backpack trial indicated that movement rate of 3–4 km/hour may reduce the percentage of successful location attempts under forest canopy. On moose, approximately 75% of attempts resulted in a location, the success rate being highest during winter/spring and lowest during fall. It is concluded that GPS has a great potential in wildlife telemetry studies, but effects of movement and habitat selection have to be addressed further.
88955003
GPS radiotelemetry error and bias in mountainous terrain
Abstrac tRadiotelemetry methods using global positioning system (GPS) technology are becomin g increasingly popular, but raw data obtained from these methods contain error and bias tha t must be addressed. We deployed GPS radiocollars at fixed locations in mountainous te r rain across a range of canopy cover and terrain conditions using nondifferentially correc t ed GPS data to test a hypothesis that these factors affect fix rates and location error in a predictable manner. Terrain did not affect fix rates in forest openings but interacted with canopy cover, resulting in lower fix rates as canopy cover increased. Horizontal diffe r ences between recorded locations and associated true locations were 5.9 m and 30.6 m , respectively, for 50% and 95% circular error probable (CEP). Absolute difference s between recorded elevations and associated true elevations were 22.9 m and 54.6 m , respectively, for 50% and 95% CEP. We rejected time of day as an influence on fix rate s and found that collar performance was a large potential source of error. We recommend that raw GPS radiotelemetry data be screened for collar malfunctions and impossible dat a (e.g., a location beyond the possible range of a study animal) prior to analysis. We su g gest that error in GPS radiotelemetry data could be decreased by considering rejection o f 2-dimensional fixes, but doing so could introduce additional biases and must be done with caution, if at all. Fix-rate bias may potentially be addressed with correction factors if pr e dictable relationships between fix rates and environmental factors exist .
88751664
Performance of two GPS telemetry collars under different habitat conditions
The recent removal of Selective Availability from satellite signals has allowed for more accurate Global Positioning System (GPS) locations without the use of differential correction. Previous studies of GPS collars have documented decreased success rates and increased positional error with increasing canopy closure, which may confound analysis of telemetry data. We tested 2 companies' collars (Lotek, Inc. and Advanced Telemetry Systems, Inc. [ATS]) for success rates, proportion of 3-dimensional (3D) fixes, and positional error under 6 habitat types with varying canopy characteristics. On average, collars were highly successful (99% Lotek and 93% ATS) and positional error (14 m [Lotek] and 16 m [ATS]) was within the manufacturers' specifications. Most (>88%) locations for both collars had positional errors of ≤25m. Success rates differed between habitat types for ATS (p=0.014) and Lotek (p<0.001) collars. The mean proportion of 3D fixes was higher for ATS collars (90%) than for Lotek (64%). Proportion of 3D fixes differed between habitats and canopy-closure classes for both collars. Success rate was negatively related to basal area but not to canopy closure. Positional error was not strongly influenced by plot basal area. Both collars performed well and offer cost-effective telemetry for medium and large animals; however, success rates were lower in plots with dense canopies. Therefore, use of areas with dense canopy closure by telemetered animals may be underestimated.
53189377
The implications of location accuracy for the interpretation of satellite-tracking data
Over the last two decades, satellite tracking with the Argos system has become a widely used tool, enabling the movements of a large variety of terrestrial, aquatic and aerial vertebrates to be recorded (e.g. Weimerskirch et al. 1992; Gudmundsson et al. 1995; McConnell & Fedak 1996; Morreale et al. 1996; Block et al. 1998; Boyd 1999; Polovina et al. 2000). The system uses transmitters (termed platform terminal transmitters or PTTs) that periodically (typically at an interval of around 60 s) send a short (typically 360–920 ms) radio signal (401.650 mHz), termed an uplink, to polar-orbiting NOAA satellites. The location of the transmitter is then calculated from the Doppler shift in the frequency of transmissions received by a satellite as it approaches and then moves away from the transmitter on a single overpass, with each location being assigned a level of accuracy. A frequent use of satellite tracking is to document long-distance animal movements of hundreds or even thousands of kilometres. When plotting tracks over such spatial scales and describing the general pattern of movement, the inaccuracy of individual locations may be unimportant (e.g. Kjellén et al. 1997). However, once more detailed aspects of Argos tracking data are considered, such as the speed of travel or small-scale movements, then location accuracy is likely to become a much more important issue. For example, the speed of travel may be determined be dividing the distance between two Argos locations by the intervening time interval, but this calculation will be compromised if this distance is short and the location inaccuracy is high. Such problems may be particularly acute in marine studies where the diving behaviour of animals can severely limit the number of uplinks received on each satellite overpass and hence a high proportion of locations may be of low quality (e.g. Plotkin 1998). It is, therefore, surprising that the implications of location accuracy, while frequently
89433871
GPS approach to study fine-scale site use by wild red deer during active and inactive behaviors
Studying fine-scale habitat selection of wild mammals relative to environmental parameters requires 1) correctly sampling the species' activity in time and space and 2) measuring the environmental variables at those locations. We propose a procedure using Differential Global Positioning System (DGPS) technology to achieve these goals. A data set from red deer (Cervus elaphus) was used to demonstrate the method. We validated an individual-based relative method using the count provided by a GPS collar activity sensor to separate active from inactive behaviors. This method allowed the correct classification of locations as active or inactive (82-97% of correct allocations depending on the fix interval used). We analyzed activity sampling using various fix intervals (5, 10, and 15 min) and the resulting spatial sampling when we retained only highly accurate locations (<10-m error radius). We demonstrated that long intervals between fixes could cause a loss of information for the shortest activity bouts, which make up 5 and 11.5% of the daily budget using 10- and 1 5-min fix intervals, respectively. The proposed spatial sampling allowed 65 to 73% of the total fixes to be kept. Active bouts were slightly undersampled, whereas inactive bouts were oversampled. We used a subsample of animal locations that were relocated using hand-held DGPS to measure several environmental variables in situ and examined the variations relative to animal and activity combinations.
16187957
Measurement error causes scale-dependent threshold erosion of biological signals in animal movement data.
Recent advances in telemetry technology have created a wealth of tracking data available for many animal species moving over spatial scales from tens of meters to tens of thousands of kilometers. Increasingly, such data sets are being used for quantitative movement analyses aimed at extracting fundamental biological signals such as optimal searching behavior and scale-dependent foraging decisions. We show here that the location error inherent in various tracking technologies reduces the ability to detect patterns of behavior within movements. Our analyses endeavored to set out a series of initial ground rules for ecologists to help ensure that sampling noise is not misinterpreted as a real biological signal. We simulated animal movement tracks using specialized random walks known as Lévy flights at three spatial scales of investigation: 100-km, 10-km, and 1-km maximum daily step lengths. The locations generated in the simulations were then blurred using known error distributions associated with commonly applied tracking methods: the Global Positioning System (GPS), Argos polar-orbiting satellites, and light-level geolocation. Deviations from the idealized Lévy flight pattern were assessed for each track after incrementing levels of location error were applied at each spatial scale, with additional assessments of the effect of error on scale-dependent movement patterns measured using fractal mean dimension and first-passage time (FPT) analyses. The accuracy of parameter estimation (Lévy mu, fractal mean D, and variance in FPT) declined precipitously at threshold errors relative to each spatial scale. At 100-km maximum daily step lengths, error standard deviations of > or = 10 km seriously eroded the biological patterns evident in the simulated tracks, with analogous thresholds at the 10-km and 1-km scales (error SD > or = 1.3 km and 0.07 km, respectively). Temporal subsampling of the simulated tracks maintained some elements of the biological signals depending on error level and spatial scale. Failure to account for large errors relative to the scale of movement can produce substantial biases in the interpretation of movement patterns. This study provides researchers with a framework for understanding the limitations of their data and identifies how temporal subsampling can help to reduce the influence of spatial error on their conclusions.
87209980
Effects of sampling effort based on GPS telemetry on home-range size estimations
Home-range size is widely used in wildlife biology to assess animal-habitat relationships. But home-range size estimation largely depends on the estimator and sample size used. Using 3 different estimators (minimum convex polygons, fixed-kernels, clusters), we used data collected on moose (Alces alces), fitted with Global Positioning System (GPS) collars (which allow automatic recording of large data sets with fewer field constraints than VHF telemetry) to investigate to what extent increasing the number of locations affects home-range size estimations. Our results indicated that 100 to 300 locations per animal annually and 30 to 100 locations seasonally were needed to reach an asymptote. High biases occurred below this asymptotic value. Minimum convex polygons consistently underestimated home-range sizes, but fixed-kernel and cluster estimators followed variable trends that often overestimated home-range sizes. Low sampling efforts also affected the number of animals needed to ensure an adequate statistical power of analysis to compare space use between 2 groups. Despite the higher cost, our findings indicate that in most instances, GPS telemetry is better suited than conventional radiotelemetry to estimate home-range sizes precisely and accurately. Moreover, this tracking technique is not limited by meteorological constraints and allows for the collection of similar sample sizes for all tracked animals, which is of major importance for further comparisons of space use among individuals.
83970501
Sensitivity of species-distribution models to error, bias, and model design: An application to resource selection functions for woodland caribou
Models that predict distribution are now widely used to understand the patterns and processes of plant and animal occurrence as well as to guide conservation and management of rare or threatened species. Application of these methods has led to corresponding studies evaluating the sensitivity of model performance to requisite data and other factors that may lead to imprecise or false inferences. We expand upon these works by providing a relative measure of the sensitivity of model parameters and prediction to common sources of error, bias, and variability. We used a one-at-a-time sample design and GPS location data for woodland caribou (Rangifer tarandus caribou) to assess one common species-distribution model: a resource selection function. Our measures of sensitivity included change in coefficient values, prediction success, and the area of mapped habitats following the systematic introduction of geographic error and bias in occurrence data, thematic misclassification of resource maps, and variation in model design. Results suggested that error, bias and model variation have a large impact on the direct interpretation of coefficients. Prediction success and definition of important habitats were less responsive to the perturbations we introduced to the baseline model. Model coefficients, prediction success, and area of ranked habitats were most sensitive to positional error in species locations followed by sampling bias, misclassification of resources, and variation in model design. We recommend that researchers report, and practitioners consider, levels of error and bias introduced to predictive species-distribution models. Formal sensitivity and uncertainty analyses are the most effective means for evaluating and focusing improvements on input data and considering the range of values possible from imperfect models.
8784125
Removing GPS collar bias in habitat selection studies
Summary 1. Compared to traditional radio-collars, global positioning system (GPS) collars provide finer spatial resolution and collect locations across a broader range of spatial and temporal conditions. However, data from GPS collars are biased because vegetation and terrain interfere with the satellite signals necessary to acquire a location. Analyses of habitat selection generally proceed without correcting for this known sampling bias. We documented the effects of bias in resource selection functions (RSF) and compared the effectiveness of two bias-correction techniques. 2. The effects of environmental conditions on the probability of a GPS collar collecting a location were modelled for three brands of collar using data collected in 24-h trials at 194 test locations. The best-supported model was used to create GPS-biased data from unbiased animal locations. These data were used to assess the effects of bias given data losses in the range of 10‐40% at both 1- and 6-h sampling intensities. We compared the sign, value and significance of coefficients derived using biased and unbiased data. 3. With 6-h locations we observed type II error rates of 30‐40% given as little as a 10% data loss. Biased data also produced coefficients that were significantly more negative than unbiased estimates. Increasing the sampling intensity from 6- to 1-h locations eliminated type II errors but increased the magnitude of coefficient bias. No type I errors or changes in sign were observed. 4. We applied sample weighting and iterative simulation given a 30% data loss. For a biased vegetation type, simulation reduced more type II errors than weighting, most probably because the original sample size was re-established. However, selection for areas near trails, which was influenced by a biased vegetation type, showed fewer type II errors after weighting existing animal locations than after simulation. Both techniques corrected 100% and ≥ 80% of the biased coefficients at the 6- and 1-h sampling intensities, respectively. 5. Synthesis and applications. This study demonstrates that GPS error is predictable and biases the coefficients of resource selection models dependant upon the GPS sampling intensity and the level of data loss. We provide effective alternatives for correcting bias and discuss applying corrections under different sampling designs.
85772559
GPS MEASUREMENT ERROR INFLUENCES ON MOVEMENT MODEL PARAMETERIZATION
Global positioning system (GPS) technology has increased the accuracy and efficiency in recording animal locations and has provided data used to parameterize move- ment models. Although numerous studies have investigated the quality and accuracy of location data associated with different brands of GPS collars, none of these studies has investigated the influence of measurement error on the parameters used to create movement models. We used Monte Carlo simulation to quantify the measurement error for estimates of turning angle and step length as a function of distance between consecutive locations. We show that estimates of turning angle and step length are accurate only when the distance between two locations is large relative to the measurement error. Estimates of turning angle are particularly susceptible to error for short step lengths. The consequences of choosing poor data-collecting schedules are discussed, and suggestions for designing appropriate data-collecting schedules are provided.
83717535
Testing the importance of spatial configuration of winter habitat for woodland caribou: An application of graph theory
Abstract Conservation of remaining woodland caribou ( Rangifer tarandus caribou ) populations requires land management strategies that not only maintain caribou habitat, but also favour habitat connectivity. This study presents and field tests graph theory-based measures of landscape connectivity, and demonstrate an association between the distribution of woodland caribou and well-connected winter habitat. Cost values for the intervening land cover types were determined based on the probability of selection relative to high-quality winter habitat. Habitat connectivity was then represented by linking high-quality habitat patches along least-cost paths through this parameterized cost surface. A randomization procedure was used to assess the animal’s association with habitat connected at increasing distance thresholds to identify appropriate scales of response. A strong relationship was obtained between large clusters of high-quality winter habitat patches and winter GPS telemetry location points (November 1–March 15) from two woodland caribou herds in Manitoba, Canada. This relationship was stronger when only late winter location points (January 1–March 15) were used. Our results highlight the importance of accounting for the spatial configuration of habitat on the landscape and the intervening land cover types when assessing range quality for woodland caribou. They also provide support for the use of graph theory to assist in identifying core activity areas for woodland caribou and key linkages between these areas and other parts of the landscape.
85577036
Overcoming radiotelemetry bias in habitat- selection studies
For many species, determination of habitat selection is based on habitat-use data obtained through radiotelemetry. Recent papers pertaining to study techniques have largely ignored the effect of habitat-dependent bias in the performance of radiotelemetry systems. Such biases cannot be overcome by increasing radiotelemetry precision, excluding data, or increasing sample sizes, as the biases are centred around data that are missing or that contain habitat-dependent errors in location. The problem is best addressed at the data-analysis stage through the use of geographic information systems. We used Monte Carlo simulations to assess the effect of habitat-dependent bias in radiotelemetry studies on the assessment of habitat selection. We looked at the effects of habitat-patch size, level of telemetry signal inhibition, level of habitat co-occurrence, and selection pattern. We demonstrated that regarding use as the composition of habitat types within a circular area around each telemetry location can help to o...
28333146
Landscape heterogeneity and the use of space by elephants in the Kruger National Park, South Africa
Landscape heterogeneity may influence ranging behaviour of mammals. Here we relate the home range size of elephants living in the Kruger National Park to the number of patches, proportion of each patch, spatial arrangement of patches, patch shape, and contrast between neighbouring patches. Home range sizes decreased exponentially with an increase in the number of patches per 100 km 2 and the
84380005
Home range and seasonal movement of elephants in the Kunene Region, northwestern Namibia
ABSTRACT This paper examines the home ranges and seasonal movements of eight GPS-collared elephants (two females and six males) in the northwestern Kunene region of Namibia. Minimum convex polygon (MCP) and the fixed kernel density estimation (FKDE) methods were used to analyse home ranges. The collared elephants showed defined home and seasonal ranges. In the eastern section of the research area, the elephants generally had smaller home ranges that were at their least during the hot and cold dry seasons, expanding during the wet season. In the western areas, the elephants moved between the Hoanib and Hoarusib Rivers in response to available vegetation that did not necessarily correspond to rainfall. The length of movement of collared elephants varied from 54.5 to 473 km in the eastern section of the research area to between 251 to 625 km in the west, over periods of up to five months.
10613109
Social dominance, seasonal movements, and spatial segregation in African elephants: a contribution to conservation behavior
The structure of dominance relationships among individuals in a population is known to influence their fitness, access to resources, risk of predation, and even energy budgets. Recent advances in global positioning system radio telemetry provide data to evaluate the influence of social relationships on population spatial structure and ranging tactics. Using current models of socio-ecology as a framework, we explore the spatial behaviors relating to the maintenance of transitive (i.e., linear) dominance hierarchies between elephant social groups despite the infrequent occurrence of contests over resources and lack of territorial behavior. Data collected from seven families of different rank demonstrate that dominant groups disproportionately use preferred habitats, limit their exposure to predation/conflict with humans by avoiding unprotected areas, and expend less energy than subordinate groups during the dry season. Hence, our data provide strong evidence of rank derived spatial partitioning in this migratory species. These behaviors, however, were not found during the wet season, indicating that spatial segregation of elephants is related to resource availability. Our results indicate the importance of protecting preexisting social mechanisms for mitigating the ecological impacts of high density in this species. This analysis provides an exemplar of how behavioral research in a socio-ecological framework can serve to identify factors salient to the persistence and management of at risk species or populations.
46915566
Rules of habitat use by elephants Loxodonta africana in southern Africa: insights for regional management
Abstract Managers in southern Africa are concerned that continually increasing elephant populations will degrade ecosystems. Culling, translocation and birth control are flawed solutions. An alternative is providing elephants more space but this hinges on identifying landscape preferences. We examined two diverse ecosystems and uncovered similarities in elephant habitat use, expressing these as ‘rules’. We considered arid Etosha National Park, (Namibia) and the tropical woodlands of Tembe Elephant Park (South Africa) and Maputo Elephant Reserve (Mozambique). Landscape data consisted of vegetation types, distances from water and settlements. To surmount issues of scale and availability we incorporated elephant movements as a function that declined as distance from an elephant's location increased. This presumes that elephants optimize trade-offs between benefiting from high-quality resources and costs to find them. Under a likelihood-based approach we determined the important variables and shapes of their relationships to evaluate and compare models separated by gender, season and location. After considering elephants' preferences for areas nearby, habitat use usually increased with proximity to water in all locations. Elephants sought places with high proportions of vegetation, especially when neighbouring areas had low vegetative cover. Lastly, elephants avoided human settlements (when present), and cows more so than bulls. In caricature, elephants preferred to move little, drink easily, eat well, and avoid people. If one makes more areas available, elephants will probably favour areas near water with high vegetative cover (of many different types) and away from people. Managers can oblige elephants’ preferences by supplying them. If so, they should anticipate higher impacts to neighbouring vegetation.
13955924
Roadless Wilderness Area Determines Forest Elephant Movements in the Congo Basin
A dramatic expansion of road building is underway in the Congo Basin fuelled by private enterprise, international aid, and government aspirations. Among the great wilderness areas on earth, the Congo Basin is outstanding for its high biodiversity, particularly mobile megafauna including forest elephants (Loxodonta africana cyclotis). The abundance of many mammal species in the Basin increases with distance from roads due to hunting pressure, but the impacts of road proliferation on the movements of individuals are unknown. We investigated the ranging behaviour of forest elephants in relation to roads and roadless wilderness by fitting GPS telemetry collars onto a sample of 28 forest elephants living in six priority conservation areas. We show that the size of roadless wilderness is a strong determinant of home range size in this species. Though our study sites included the largest wilderness areas in central African forests, none of 4 home range metrics we calculated, including core area, tended toward an asymptote with increasing wilderness size, suggesting that uninhibited ranging in forest elephants no longer exists. Furthermore we show that roads outside protected areas which are not protected from hunting are a formidable barrier to movement while roads inside protected areas are not. Only 1 elephant from our sample crossed an unprotected road. During crossings her mean speed increased 14-fold compared to normal movements. Forest elephants are increasingly confined and constrained by roads across the Congo Basin which is reducing effective habitat availability and isolating populations, significantly threatening long term conservation efforts. If the current road development trajectory continues, forest wildernesses and the forest elephants they contain will collapse.
84035268
Elephant seasonal vegetation preferences across dry and wet savannas
As African savanna elephants (Loxodonta africana) become increasingly confined to smaller fragmented landscapes, concern over their potential detrimental impacts on vegetation and biodiversity has increased. Understanding elephant vegetation preferences across relevant spatial and temporal scales is a critical step towards managing protected areas for the persistence of both elephants and biodiversity. To better understand elephant vegetation selection, we fitted 68 elephants with GPS collars across a strong rainfall gradient spanning seven southern African countries over a period of 6 years. We compared elephant locations with remotely-sensed environmental data that measure bi-monthly vegetation greenness across the study area. Elephants consistently seek out greener than expected vegetation throughout the year. Interestingly, they do so by utilizing vegetation with different phenologies and by selecting landscapes when they are greener than their surroundings. We found no differences between dry and wet savannas. These patterns persist even when elephants are constrained by seasonally available water. In the wet season, elephants select seasonally variable landscapes such as open woodlands, shrublands, and grasslands. These landscapes have a lower average annual greenness but become very green for a few months in the wet season. In the dry season, elephants prefer less variable landscapes that are more consistently green year-round such as well-wooded areas and closed woodlands. Because elephants prefer different vegetation types at different times of the year, small homogeneous protected areas may be unsuitable for elephants. Since elephants prefer woody vegetation during the dry season when they are constrained by water, human actions that increase dry season water availability may contribute to detrimental elephant impacts on vegetation and biodiversity.
23158133
Density as an explanatory variable of movements and calf survival in savanna elephants across southern Africa.
1. Southern Africa's 'elephant problem' is often attributed to an overabundance of elephants (Loxodonta africana) in conservation areas. Paradoxically, the African elephant is listed as 'vulnerable' (IUCN Redlist) despite occupying a large geographical range and numbering about 600 000. How densities influence elephant populations is therefore important for conservation management decisions, particularly because a move towards non-equilibrium management of savannas implies a need for elephant populations to fluctuate in response to variation in intrinsic (demographic) and extrinsic (resource) factors. 2. A study on one of the world's largest elephant populations demonstrated that population regulation is driven by a spatial response to water availability, environmental stochasticity and density. The challenge remains to identify the demographic and behavioural variables that drive density dependence. 3. We evaluated whether the movements of elephant family groups from 13 populations across a wide resource gradient were explained by variability in primary productivity, rainfall and population density. We then assessed whether density-related movements explained variability in juvenile survival, hence inferring a spatially driven behavioural mechanism that may explain density-dependent population growth. We also analysed whether management actions modified this mechanism. 4. In the dry season, daily-displacement distances (DDDs) increased non-linearly with density, and declined with increased vegetation productivity and previous wet season rainfall. In the wet season, DDDs were primarily explained by vegetation productivity. 5. The survival of weaned calves (4-7 years) decreased with increasing dry season DDDs, but this did not hold for suckling calves (1-3 years) or sub-adults (8-11 years). 6. Fences and supplementary water modified the shape and strength of relationships between DDDs and densities, vegetation productivity and rainfall and negated the relationships between DDDs and weaned calf survival. 7. We suggest that density dependence in weaned calf survival is driven by the response of dry season roaming activities of family groups to variations in density, rainfall and the distribution of food. Fences and supplementary water that alter this mechanism may contribute to the relatively high population growth rates of some populations.
20820573
Are All Global Positioning System Collars Created Equal? Correcting Habitat-Induced Bias Using Three Brands in the Central Canadian Rockies
Abstract Global positioning system (GPS) collars are changing the face of wildlife research, yet they still possess biases such as habitat-induced fix-rate bias, which is a serious concern for habitat selection studies. We studied GPS bias in the Central Canadian Rockies, a critical area for wildlife conservation, to provide a statistical approach to correct GPS habitat bias for habitat selection studies using GPS collars. To model GPS habitat bias we deployed 11 different collars from 3 brands of GPS collars (Advanced Telemetry Systems [ATS], Asanti, MN; LOTEK Engineering Ltd., Newmarket, ON, Canada; and Televilt, Lindesberg, Sweden) in a random-stratified design at 86 sites across habitat and topographic conditions. We modeled the probability of obtaining a successful location, PFIX, as a function of habitat, topography, and collar brand using mixed-effects logistic regression in an information theoretic approach. For LOTEK collars, we also investigated the effect of 8 and 12 GPS channels on fix rate. The ATS collars had the highest overall fix rates (97.4%), followed by LOTEK 12 channel (94.5%), LOTEK 8 channel (85.6%), and Televilt (82.3%). Sufficient model selection uncertainty existed to warrant model averaging for logistic regression PFIX models. Collar brand influenced fix rate in all PFIX models: fix rates for ATS and LOTEK 12 channel were not statistically different, whereas LOTEK 8 channel receivers had intermediate fix rates, and Televilt had the lowest. Fix rate was reduced in aspen stands, closed coniferous stands, and sites in narrow mountainous valleys but was higher on upper mountain slopes. Slight discrepancies between fix rates from field trials and observed species fix rates (wolf [Canis lupus] and elk [Cervus elaphus]) suggest uncorrected behavioral or movement-induced bias similar to other recent studies. Regardless, the strong habitat-induced bias in GPS fix rates confirms that in our study area habitat effects are critical, especially for poorer performance brands. Based on previous studies of effects of the amount of bias on inferences, our results suggest correction for GPS bias should be mandatory for Televilt collars in the Canadian Rockies, optional for LOTEK (dependent on the no. of channels), and unnecessary for ATS. Thus, our GPS bias model will be useful to researchers using GPS collars on a variety of species throughout the Rocky Mountain cordillera.
85327506
Influence of topography and GPS fix interval on GPS collar performance
Abstract Topography, vegetation, and animal behavior may influence the performance of Global Positioning System (GPS) telemetry collars, affecting fix success rates and location error. We reviewed the scientific literature published from 1995 to June 2004 to determine the fix intervals used and fix success rates obtained in studies using GPS telemetry. We also programmed GPS telemetry collars with 6 different fix intervals and placed them at fixed locations of varying topography in the Cabeza Prieta National Wildlife Refuge, Arizona from August 2003–May 2004. Fix interval affected fix success rates both in our field study (99, 98, 96, 94, 93, 92% fix success rate for 0.25, 0.5, 1, 4, 6, and 13-hour fix intervals, respectively) and in our analysis of data obtained from scientific literature (r2=0.531, P≤0.001), with shorter fix intervals being associated with higher fix success rates. Topography affected the fix success rate (F2, 77=12.017, P≤0.001), location error (F2, 77=6.76, P=0.002), and proportion of 3-dimensional (3-D) fixes (F2,77=10.184, P≤0.001), resulting in lower fix success rates and larger location errors in areas with more rugged topography. The influence of topography and fix interval on location error and fix success rates may bias GPS location data, resulting in misclassification of habitat use and under-sampling certain areas used by animals. Location error and missing data can increase type II error and may result in incorrect inferences in some studies. These biases need to be assessed and steps should be taken to minimize their influence on results of studies of habitat selection and other aspects of animal ecology.
84304356
Performance of Gps Telemetry Collars for Red Deer Cervus Elaphus in Rugged Alpine Terrain Under Controlled and Free-living Conditions
Abstract In mountainous terrain, performance of VHF telemetry is often impaired by long distances between observer and animal, and by reflections of radio signals. GPS telemetry should be less affected by such constraints, but its performance has not been sufficiently tested in areas of rugged topography. We studied how current GPS telemetry deployed on red deer Cervus elaphus performs in the strong topographic relief of a rugged Alpine landscape. We examined the influence of topography, vegetation and red deer activity on GPS performance, assessed the accuracy of 2D positions of red deer and compared differences in GPS performance between collars in trials and collars fitted to deer. GPS performance was characterised by consistently high position acquisition rates (PAR), but a relatively low proportion of 3D positions compared to smoother terrain. The proportion of 3D positions was lower in forest than in open land but within forest different vegetation structures had only a weak influence. For collars fitted to red deer, we found that > 70% of the positions were either 3D positions or accurate 2D positions. The collars produced higher PAR and proportions of 3D positions in the trials than when they were fitted to red deer, probably reflecting an effect of red deer behaviour. We also observed better performance of collars on red deer during night than during daytime, because animals were more active at night where they more often occurred in open land. An effect of season on the proportion of 3D positions was found in collars fitted to red deer, but not in the trials, and may be interpreted as a secondary effect produced by seasonal differences in habitat selection by red deer. The fact that PAR was not affected more strongly by the rugged mountainous relief probably reflects the recent progress achieved in GPS technology, whereas the comparatively low proportion of 3D positions illustrates that the probability of four satellites being available at any one time is still constrained by topography.
84237730
Accuracy, Precision, and Observation Rates of Global Positioning System Telemetry Collars
Abstract We addressed concerns regarding performance of various Global Positioning System (GPS) collar configurations for describing habitat use by Rocky Mountain elk (Cervus elaphus) in rugged, forested terrain. We tested 8 GPS collars (Lotek Wireless, Newmarket, ON, Canada) in 4 different model and equipment configurations at 2 reference points (an open hilltop and a forested ravine) to determine habitat-specific differences in performance among collar configurations. We then placed individual collars at 60 additional points that were stratified randomly among 4 canopy-cover classes and 3 classes of available sky. All collars exhibited a locational bias of 4 m horizontally west and of 10 m vertically below a reference standard established by position-averaging with a handheld receiver (Garmin 12MAP) calibrated at National Geodetic Survey benchmarks. The GPS collar models that were programmed for longer satellite-acquisition times provided greater location precision than models that had been programmed for short acquisition times to preserve battery power. Canopy cover and available sky had a greater effect on collar location precision and observation rates than slope, slope position, aspect, conifer basal area, tree height, canopy depth, or elevation. Researchers should test collars at known reference points to confirm that location precision and rates of observation are adequate for their particular study objectives. Manufacturers of GPS collars should inform clients of their programming criteria for acquisition time so that customers can make informed decisions regarding trade-offs between precision of locations, data quantity, and battery life.
81989107
Evaluation of a GPS collar for white-tailed deer.
New collar designs should be tested in controlled settings to determine whether accuracy is comparable to currently available technology. We evaluated a new Global Positioning System (GPS) collar for white-tailed deer (Odocoileus virginianus) to determine whether positional accuracy was comparable to previous literature and whether behavior of collared animals or vegetation characteristics affected positional accuracy. We collared 5 male white-tailed deer at the enclosed Wildlife Research and Education Facility at Mississippi State University. We observed deer from a fixed observation stand. We recorded behavior, head position, and location of deer when GPS collars attempted to acquire a location. Global Positioning System collars collected locations on 85% of the attempts. Positional error was not affected by behavior (i.e., bedded, moving, or standing) or head position (i.e., down, mixed, up, P>0.05). Ability of the GPS collar to acquire a fix was affected by behavior (P<0.001), but not by head position (P=0.099). Vegetation characteristics (i.e., basal area, canopy coverage, and distance to nearest tree) did not affect ability of GPS collars to acquire a fix, although there was a narrow range of vegetation characteristics within the captive deer facility. This new GPS collar design can be used cost-effectively to obtain animal locations with great accuracy and precision and with little operator or equipment error.