lSUNY College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse, NY 13210, USA 2Biometrics Unit, Minnesota Department of Natural Resources, 5463-C W, Broadway Forest Lake, MN 55025, USA 3 Wildlife Biology Program, College of Forestry and Conservation, University of Montana, Missoula, MT 59812, USA 4Research and Innovation Centre, Environment and Natural Resources Area, Edmund Mach Foundation, 38010 San Michele alVAdige, Trento, Italy 5Stelvio National Park, 23032 Bormio, Sondrio, Italy

/pdf/resolving-issues-of-imprecise-and-habitat-biased-locations-2hxznbopmn.pdf

Resolving issues of imprecise and habitat-biased locations in ecological analyses using GPS telemetry data.

Animals selecting habitats often have to consider many factors, e.g., food and cover for safety. However, each habitat type often lacks an adequate mixture of these factors. Analyses of habitat selection using resource selection functions (RSFs) for animal radiotelemetry data typically ignore trade-offs, and the fact that these may change during an animal's daily foraging and resting rhythm on a short-term basis. This may lead to changes in the relative use of habitat types if availability differs among individual home ranges, called functional responses in habitat selection. Here, we identify such functional responses and their underlying behavioral mechanisms by estimating RSFs through mixed-effects logistic regression of telemetry data on 62 female red deer (Cervus elaphus) in Norway. Habitat selection changed with time of day and activity, suggesting a trade-off in habitat selection related to forage quantity or quality vs. shelter. Red deer frequently used pastures offering abundant forage and little canopy cover during nighttime when actively foraging, while spending much of their time in forested habitats with less forage but more cover during daytime when they are more often inactive. Selection for pastures was higher when availability was low and decreased with increasing availability. Moreover, we show for the first time that in the real world with forest habitats also containing some forage, there was both increasing selection of pastures (i.e., not proportional use) and reduced time spent in pastures (i.e., not constant time use) with lowered availability of pastures within the home range. Our study demonstrates that landscape-level habitat composition modifies the trade-off between food and cover for large herbivorous mammals. Consequently, landscapes are likely to differ in their vulnerability to crop damage and threat to biodiversity from grazing.

/pdf/temporal-scales-trade-offs-and-functional-responses-in-red-3wriimwaak.pdf

Temporal scales, trade-offs, and functional responses in red deer habitat selection

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.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2664.2007.01286.x

Effects of habitat on GPS collar performance: using data screening to reduce location error

Do domestic cats impose an unsustainable harvest on urban bird populations

Animal locations estimated by Global Positioning System (GPS) inherently contain errors. Screening procedures used to remove large positional errors often trade data accuracy for data loss. We developed a simple screening method that identifies locations arising from unrealistic movement patterns. When applied to a large data set of moose (Alces alces) locations, our method identified virtually all known errors with minimal loss of data. Thus, our method for screening GPS data improves the quality of data sets and increases the value of such data for research and management.

https://bioone.org/journals/journal-of-wildlife-management/volume-74/issue-6/2009-405/Screening-Global-Positioning-System-Location-Data-for-Errors-Using-Animal/10.2193/2009-405.pdf

Screening Global Positioning System Location Data for Errors Using Animal Movement Characteristics

Summary


1
Global positioning system (GPS) radio-telemetry has become an important wildlife research technique worldwide. However, understanding, quantifying and managing error and bias in raw GPS radio-telemetry data sets requires much more work. In particular, error and bias resulting from position (angle away from vertical) and orientation (compass direction) of GPS radio-collars on free-ranging animals is currently unknown.

2
We tested the effects of collar position and orientation on GPS radio-collar performance using five stationary GPS radio-collars. We also investigated the use of positional dilution of precision (PDOP) as a method for screening data with high location errors.

3
Orientation had no statistical effect on fix rates or location errors. The biggest source of variation was attributed to collar position, which resulted in significantly lower performance at angles below 90° from vertical.

4
PDOP-based screening was effective and can be used to lower location error, but the trade-off between higher location accuracy and data loss (potentially leading to new bias) must be assessed.

5
Synthesis and applications. The results of this study refine our understanding of error and bias in GPS radio-telemetry data. We suggest that collar orientation can safely be disregarded, whereas radio-collar position remains a large potential source of error and bias. This finding has major implications regarding animal activity and GPS radio-telemetry research. Researchers need to quantify and account for biases resulting from animals moving through heterogeneous terrain and habitats.

Effects of radio‐collar position and orientation on GPS radio‐collar performance, and the implications of PDOP in data screening

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Effects of radio‐collar position and orientation on GPS radio‐collar performance, and the implications of PDOP in data screening