Evaluation of Solar-Powered GPS Ear Tags and Long-Range Data Transmission for Use in Wildlife Research: Case Study of Collared Peccary (Pecari tajacu)

Technical Summary: Evaluation of Solar-Powered GPS Ear Tags and LoRaWAN for Wildlife Research

Problem Statement
Global Positioning System (GPS) technology is a cornerstone of wildlife monitoring, yet datasets are frequently compromised by data loss (missing fixes) and horizontal error. These biases, often caused by vegetation canopy masking satellite signals, can lead to inaccurate ecological inferences regarding space use and resource selection. While traditional GPS collars store data locally (requiring physical retrieval) or use expensive satellite transmission (e.g., Iridium), emerging Internet of Things (IoT) technologies offer a low-cost alternative. Specifically, Long Range Wide Area Network (LoRaWAN) combined with solar-powered GPS tracking presents a potential solution for near real-time data retrieval without high transmission fees. However, the efficacy of these integrated systems in wildlife contexts—particularly for species utilizing dense vegetation—remains under-evaluated. There is a critical need to determine if solar-powered, LoRaWAN-enabled tags can maintain sufficient battery life and fix success rates in environments where animals seek cover, which limits solar recharge and signal transmission.

Methodology
The study evaluated mOOvement solar-powered GPS ear tags (30–37 g) equipped with LoRaWAN data transmission capabilities through two distinct phases: stationary testing and on-animal deployment.

• Study Sites: Testing occurred at two locations in southern Texas: La Copita Demonstration Area and Research Ranch (1,103 ha) and the Chaparral Wildlife Management Area (CWMA; 6,151 ha). Both sites feature dense thorny shrublands but differ in vegetation structure and density.
• Stationary Testing: Researchers deployed 410 tags (225 at La Copita, 185 at CWMA) across linear transects extending up to 7.4 km from LoRaWAN antennas. Tags were mounted on stakes at 100 m (La Copita) or 200 m (CWMA) intervals. At each point, five tags were oriented in different directions (North, South, East, West, Up) to test orientation effects. The study recorded woody cover (%) using the Rangeland Analysis Platform (30-m resolution) and calculated Euclidean distances to the antenna. Tags were programmed to record one GPS fix per hour for 48 hours.
• On-Animal Deployment: Ten collared peccaries (Pecari tajacu) were captured, chemically immobilized, and fitted with the tags. Nine tags successfully transmitted data. Vital signs and morphometrics were recorded, and animals were released after recovery.
• Data Analysis: Fix success (proportion of attempted fixes received) and horizontal error (Euclidean distance between recorded and true locations) were analyzed using Generalized Linear Mixed Models (GLMMs). Covariates included woody cover, distance to the antenna, and their interaction. Battery voltage trends were analyzed to assess solar recharge efficiency under varying vegetation conditions.

Key Results

• Fix Success: Overall fix success during stationary testing was moderate: 58.2% at La Copita and 51.2% at CWMA. At La Copita, fix success significantly decreased as woody cover and distance to the antenna increased, particularly when these factors acted in combination. Conversely, at CWMA, neither woody cover nor distance significantly influenced fix success.
• Horizontal Error: Neither woody cover nor distance to the antenna significantly affected horizontal error at either site. The average horizontal error was 21.7 m at La Copita and 26.9 m at CWMA.
• Battery Performance: Battery voltage was highly sensitive to woody cover. At La Copita, tags in denser cover experienced rapid voltage decline, with projections suggesting a drop below the transmission threshold (3.91 V) within ~100 days under continuous dense cover. At CWMA, tags in low-to-moderate cover maintained or slightly increased voltage.
• On-Animal Deployment: Of the 10 peccaries, one tag failed immediately. The remaining nine transmitted data for an average of 5.6 days (range: 3–7 days) before battery voltage declined below the operational threshold. During this period, average fix success was 41.0%. The rapid failure was attributed to the species' behavior: collared peccaries frequently occupied dense woody cover (averaging 85.4% cover during midday), preventing solar recharge during peak sunlight hours.

Key Contributions
This study provides one of the first rigorous evaluations of solar-powered, LoRaWAN-enabled GPS ear tags on a wildlife species known for utilizing dense cover. The research highlights that the performance of these devices is not solely a function of hardware but is deeply dependent on the interaction between local environmental conditions (vegetation structure, antenna proximity) and species-specific ecology (habitat selection and activity patterns). The study demonstrates that while LoRaWAN offers a cost-effective transmission method, the reliance on solar recharge creates a vulnerability for species that seek shade during the day, leading to rapid battery depletion and shortened data collection windows.

Significance and Claims
The authors conclude that solar-powered, LoRaWAN GPS ear tags may offer a relatively low-cost option for wildlife telemetry, but their application is constrained by environmental and behavioral factors. The paper claims that these tags are best suited for medium- to large-bodied species that regularly occupy open habitats where solar recharge is reliable. For species like the collared peccary that frequently seek dense cover, the technology's dependence on solar energy results in significant limitations in battery longevity and data recovery.

The authors emphasize that researchers must carefully evaluate habitat conditions, species behavior, and spatial-resolution requirements before large-scale deployment. They suggest that pilot testing is essential to determine if the observed fix success rates (51–58%) and positional errors (~22–27 m) are sufficient for specific study objectives, particularly noting that the horizontal error is greater than that of traditional GPS collars. Ultimately, the paper argues that matching tracking technology to the ecological characteristics of the focal species is critical, and that current limitations in solar recharge efficiency under dense canopy may restrict the utility of these devices for certain wildlife applications.