Effects of Variable Sampling Frequencies on GPS Transmitter Efficiency and Estimated Wolf Home Range Size and Movement Distance

Abstract

Global positioning system (GPS) technology has greatly improved the ability to investigate animal ecology at fine spatial and temporal scales but many GPS telemetry-based investigations may be underutilizing the technical capabilities of modern transmitters. We estimated eastern timber wolf (Canis lycaon) movement distance and territory size using variable GPS transmitter sampling frequencies to evaluate the effect of programming details on estimated movement patterns, territory size, and transmitter performance. Estimated movement distance decreased exponentially as sampling frequency was reduced from 1 location every 5 minutes to 1 location every 24 hours, implying that intense sampling frequencies were required for accurate measurement of finescale wolf movements. Wolf territory size estimates using 95% minimum convex polygons declined with decreasing sampling frequency, whereas estimates using adaptive kernel methods were comparable across a range of sampling intensities. Estimated transmitter battery longevity increased as the interval between fixes was lengthened but transmitter efficiency, defined as the number of successful fixes obtained during battery lifespan of the transmitter, was highest with fix intervals of intermediate length.Although GPS transmitters are effective for documenting fine-scale movements of animals, we argue their performance is strongly dependent upon transmitter programming and scale of analysis. Effective use of GPS transmitters will require study-specific assessment of the trade-offs between sampling needs versus transmitter efficiency and longevity.

Maned Wolves of Noel Kempff Mercado National Park

“…GPS telemetry underestimates the true path length of an animal by an amount related to the intrinsic straightness of the path and the interval between locations (Mills et al, 2006). Actual maned wolf travel distances, from the difference between hourly and half-hourly data, were on average at least 1.2 km per night longer than those estimated from hourly fixes, or 12.2 km global nightly average.…”

“…When we briefly followed a vHF-collared zorro, it, too, moved much faster than is usual for MW (Emmons, unpublished data). Gray wolves in summer moved mean distances of 21 km per 24 hour day, at a mean rate of 830 m/h (Mills et al, 2006, data from GPS collars), with rests included in hourly rate calculations. Compared with our data, in which movement rates include only hours of active travel, Mills et al (2006) would underestimate wolf travel speed.…”

“…Gray wolves in summer moved mean distances of 21 km per 24 hour day, at a mean rate of 830 m/h (Mills et al, 2006, data from GPS collars), with rests included in hourly rate calculations. Compared with our data, in which movement rates include only hours of active travel, Mills et al (2006) would underestimate wolf travel speed. The long legs of MW thus are not associated with greater travel distances per night or per hour than those reported for shorter-limbed Canidae that travel with the efficient, longdistance, diagonal trot.…”

“…By connecting sequential locations into a route, a greater area traversed can be inferred than can be seen from individual fixes, but nightly routes neither reliably include quick visits to point resources nor generate time budgets such as can be developed with continuous observation . The information acquired from GPS telemetry obviously depends on the scheduling of the GPS fixes: the closer they are in time, the more accurately the fixes map the path and the more exact spots visited are recorded (Mills et al, 2006). GPS telemetry technology has rapidly improved since we began our work, and soon, battery life may no longer be an issue (Tobler, 2009).…”

Global positioning system and associated technologies in animal behaviour and ecological research

“…Telemetry system performance is important information for designing studies (Ryan et al 2004;Mills et al 2006;Horne et al 2007;Mitchell & Powell 2008;Godvik et al 2009). If the user is unfamiliar with the equipment, or if it is being used for the first time on a species or in an unusual landscape, ample time should be allowed to test functions of the radio telemetry 'system'.…”