Eyes on the herd: Quantifying ungulate density from satellite, unmanned aerial systems, and GPScollar data

Abstract

Novel approaches to quantifying density and distributions could help biologists adaptively manage wildlife populations, particularly if methods are accurate, consistent, cost-effective, rapid, and sensitive to change. Such approaches may also improve research on interactions between density and processes of interest, such as disease transmission across multiple populations. We assess how satellite imagery, unmanned aerial system (UAS) imagery, and Global Positioning System (GPS) collar data vary in characterizing elk density, distribution, and count patterns across times with and without supplemental feeding at the National Elk Refuge (NER) in the US state of Wyoming. We also present the first comparison of satellite imagery data with traditional counts for ungulates in a temperate system. We further evaluate seven different aggregation metrics to identify the most consistent and sensitive metrics for comparing density and distribution across time and populations. All three data sources detected higher densities and aggregation locations of elk during supplemental feeding than non-feeding at the NER. Kernel density estimates (KDEs), KDE polygon areas, and the first quantile of interelk distances detected differences with the highest sensitivity and were most highly correlated across data sources. Both UAS and satellite imagery provide snapshots of density and distribution patterns of most animals in the area at lower cost than GPS collars. While satellite-based counts were lower than traditional counts, aggregation metrics matched those from UAS and GPS data sources when animals appeared in high contrast to the landscape, including brown elk against new snow in open areas. UAS counts of elk were similar to traditional groundbased counts on feed grounds and are the best data source for assessing changes in small spatial extents. Satellite, UAS, or GPS data can provide appropriate data for assessing density and changes in density from adaptive management actions. For the NER, where high elk densities are beneath controlled Tabitha A. Graves and Michael J. Yarnall are co-lead authors.

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“…In line with Graves et al . [ 39 ] we also calculated 25% quantiles, which were 0.32 and 0.49 m for grey and harbour seals, respectively. These quartiles also significantly differed between species ( t -value 8.32539, p < 0.001).…”

Estimating the abundance of a group‐living species using multi‐latent spatial models

“…Potential extensions include the use of environmental covariates as described above, as well as explicitly modelling the temporal dynamics of the wildebeest herds (Blangiardo et al, 2013). The greater flexibility of the model translates to greater flexibility in the field when conducting the survey, as well as the prospect of including multiple species in the analysis and incorporating data from multiple sources (Graves et al, 2022;Robinson et al, 2021). F I G U R E 4 Posterior distribution of wildebeest abundance.…”

How Many Reindeer? UAV Surveys as an Alternative to Helicopter or Ground Surveys for Estimating Population Abundance in Open Landscapes

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