Inferred Spatial use by Elephants is Robust to Landscape Effects on GPS Telemetry

Ott, Theresia; Aarde, Rudi J. van

doi:10.3957/056.040.0204

Cited by 5 publications

(5 citation statements)

References 31 publications

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“…Average location error in our study was strongly reduced by 1) eliminating 2‐D fixes from data sets with long fix intervals or periods without satellite information, and/or 2) eliminating all 2‐D fixes after a series of failed fixes until a 3‐D fix was obtained. As demonstrated in previous studies (Lewis et al , Ott and van Aarde ), removing all 2‐D fixes results in data loss and further biases data (Cargnelutti et al ). However, in cold‐start mode mimicking fix intervals >4 hr, every 2‐D fix was inaccurate (>198 m).…”

Section: Discussionmentioning

confidence: 76%

“…In complex patches with dense forest cover and a multistory canopy, the GPS devices we used were 6.6× less likely (11% vs. 69% fix success) to obtain a fix when in cold‐start mode than when in continuous mode. Fix success rates <50% may be typical in areas with vegetation obstructions and fix intervals greater than the interval for which ephemeris data are valid (i.e., 1–4 hr; Sager‐Fradkin et al , Blackie , Ott and van Aarde ). Our controlled experiment suggests that the combination of vegetation obstruction and lack of satellite information imposes substantial GPS bias on many data sets.…”

Section: Discussionmentioning

confidence: 99%

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Retained satellite information influences performance of GPS devices in a forested ecosystem

Moriarty

Epps

2015

Wildl. Soc. Bull.

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Global Positioning System (GPS) units used in animal telemetry often suffer from nonrandom data loss and location error. GPS units use stored satellite information to estimate locations, including almanac and ephemeris data reflecting satellite positions at weekly and at <4‐hr temporal scales, respectively. Using the smallest GPS collars (45–51 g) available for mammals, we evaluate how satellite information and environmental conditions affected GPS performance in 27 mobile trials, and field reliability during 56 deployments on Pacific marten (Martes caurina). We conducted trials in Lassen National Forest, California, USA, during March 2011–January 2012. We programmed GPS units to retain or remove satellite data (i.e., continuous or cold‐start mode) before attempting a location (fix), thereby mimicking differing fix intervals. In continuous mode, fix success was 2.2× higher, was not influenced by environmental obstructions, and improved after a location with ≥4 satellites (3 ‐D). In cold‐start mode, fix success was negatively correlated with vegetation cover. Location error was lower for 3‐D fixes. Censoring cold‐start fixes with only 3 satellites (2‐D) and 2‐D locations prior to the first 3‐D fix in continuous mode decreased location error by 91% and 55%, ensuring <50 m accuracy. The significance of previous fix success and reduced battery expenditure underscores the benefits of ephemeris data and short fix intervals. Only 66% of 56 units functioned upon delivery for field deployment. Once tested and deployed, 28% malfunctioned. This study demonstrates that GPS tests should use the same fix schedules as field deployments, and GPS data quality in dense cover improves with short fix intervals. Miniature GPS units are a promising tool, but the study design should be carefully considered. © 2015 The Wildlife Society.

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Section: Discussionmentioning

confidence: 76%

Section: Discussionmentioning

confidence: 99%

Retained satellite information influences performance of GPS devices in a forested ecosystem

Moriarty

Epps

2015

Wildl. Soc. Bull.

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“…For instance, the impacts of free-ranging forest elephants depend largely on what they are doing at very speci c localities [139,140]. At present, GPS is mostly used to re ect on where elephants move as a general response to the availability of resources such as food, water and safety [e.g., 139,141,142]. Driftcorrected dead-reckoning can highlight the speci cs of behaviours and localities, and therefore, for example, allow researchers to retrace elephant movements to determine what elephants feed on and where they do it, which has obvious management value.…”

Section: The Utility Of Dead-reckoningmentioning

confidence: 99%

How Often Should Dead-Reckoned Animal Movement Paths be Corrected for Drift?

Gunner

Holton

Scantlebury

et al. 2021

Preprint

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BackgroundUnderstanding what animals do in time and space is important for a range of ecological questions, however accurate estimates of how animals use space is challenging. Within the use of animal-attached tags, radio telemetry (including the Global Positioning System (GPS)) is typically used to verify an animal’s location periodically. Straight lines are typically drawn between these ‘Verified Positions’ (VPs) so the interpolation of space-use is limited by the temporal- and spatial resolution of the system’s measurement. As such, parameters such as route-taken and distance travelled can be poorly represented when using VP systems alone. Dead-reckoning has been suggested as a technique to improve the accuracy and resolution of reconstructed movement paths, whilst maximising battery life of VP systems. This typically involves deriving travel vectors from motion sensor systems and periodically correcting path dimensions for drift with simultaneously deployed VP systems. How often paths should be corrected for drift, however, has remained unclear.Methods & ResultsHere, we review the utility of dead-reckoning across four contrasting model species using different forms of locomotion (the African lion Panthera leo, the Red-tailed tropicbird Phaethon rubricauda, the Magellanic penguin Spheniscus magellanicus, and the Imperial cormorant Leucocarbo atriceps). Simulations were performed to examine the extent of dead-reckoning error, relative to VPs, as a function of Verified Position correction (VP correction) rate and the effect of this on estimates of distance moved. Dead-reckoning error was greatest for animals travelling within air and water. We demonstrate how sources of measurement error can arise within VP-corrected dead-reckoned tracks and propose advancements to this procedure to maximise dead-reckoning accuracy.ConclusionsWe review the utility of VP-corrected dead-reckoning according to movement type and consider a range of ecological questions that would benefit from dead-reckoning, primarily concerning animal-barrier interactions and foraging strategies.

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“…For instance, the impacts of free-ranging forest elephants depend largely on what they are doing at very specific localities [145,146]. At present, GPS is mostly used to reflect on where elephants move as a general response to the availability of resources such as food, water and safety (e.g., [145,147,148]). Drift-corrected dead-reckoning can highlight the specifics of behaviours and localities, and therefore, for example, allow researchers to retrace elephant movements to determine what elephants feed on and where they do it, which has obvious management value.…”

Section: The Utility Of Dead-reckoningmentioning

confidence: 99%

How often should dead-reckoned animal movement paths be corrected for drift?

et al. 2021

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Background Understanding what animals do in time and space is important for a range of ecological questions, however accurate estimates of how animals use space is challenging. Within the use of animal-attached tags, radio telemetry (including the Global Positioning System, ‘GPS’) is typically used to verify an animal’s location periodically. Straight lines are typically drawn between these ‘Verified Positions’ (‘VPs’) so the interpolation of space-use is limited by the temporal and spatial resolution of the system’s measurement. As such, parameters such as route-taken and distance travelled can be poorly represented when using VP systems alone. Dead-reckoning has been suggested as a technique to improve the accuracy and resolution of reconstructed movement paths, whilst maximising battery life of VP systems. This typically involves deriving travel vectors from motion sensor systems and periodically correcting path dimensions for drift with simultaneously deployed VP systems. How often paths should be corrected for drift, however, has remained unclear. Methods and results Here, we review the utility of dead-reckoning across four contrasting model species using different forms of locomotion (the African lion Panthera leo, the red-tailed tropicbird Phaethon rubricauda, the Magellanic penguin Spheniscus magellanicus, and the imperial cormorant Leucocarbo atriceps). Simulations were performed to examine the extent of dead-reckoning error, relative to VPs, as a function of Verified Position correction (VP correction) rate and the effect of this on estimates of distance moved. Dead-reckoning error was greatest for animals travelling within air and water. We demonstrate how sources of measurement error can arise within VP-corrected dead-reckoned tracks and propose advancements to this procedure to maximise dead-reckoning accuracy. Conclusions We review the utility of VP-corrected dead-reckoning according to movement type and consider a range of ecological questions that would benefit from dead-reckoning, primarily concerning animal–barrier interactions and foraging strategies.

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Inferred Spatial use by Elephants is Robust to Landscape Effects on GPS Telemetry

Cited by 5 publications

References 31 publications

Retained satellite information influences performance of GPS devices in a forested ecosystem

Retained satellite information influences performance of GPS devices in a forested ecosystem

How Often Should Dead-Reckoned Animal Movement Paths be Corrected for Drift?

How often should dead-reckoned animal movement paths be corrected for drift?

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