Estimating kangaroo density by aerial survey: a comparison of thermal cameras with human observers

Abstract

ContextAerial surveys provide valuable information about the population status and distribution of many native and pest vertebrate species. They are vital for evidence-based monitoring, budget planning and setting management targets. Despite aircraft running costs, they remain one of the most cost-effective ways to capture distribution and abundance data over a broad area. In Australia, annual surveys of large macropods are undertaken in several states to inform management, and in some jurisdictions, to help set commercial kangaroo harvest quotas. Improvements in the cost efficiencies of these surveys are continually sought. Aerial thermal imaging techniques are increasingly being tested for wildlife surveys, but to date no studies have directly compared population data derived from thermal imaging with data collected by human observers during the same flight. AimsDuring an aerial survey of western grey kangaroos (Macropus fuliginosus), eastern grey kangaroos (M. giganteus) and red kangaroos (Osphranter rufus) across the state of Victoria, Australia, the objective was to conduct a direct comparison of the effectiveness of thermal camera technology and human observers for estimating kangaroo populations from aerial surveys. MethodsA thermal camera was mounted alongside an aerial observer on one side of the aircraft for a total of 1360km of transect lines. All thermal footage was reviewed manually. Population density estimates and distance sampling models were compared with human observer counts. Key resultsOverall, the kangaroo density estimates obtained from the thermal camera data were around 30% higher than estimates derived from aerial observer counts. This difference was greater in wooded habitats. Conversely, human-derived counts were greater in open habitats, possibly due to interference from sunlight and flushing. It was not possible to distinguish between species of macropod in the thermal imagery. ConclusionsThermal survey techniques require refining, but the results of the present study suggest that with careful selection of time of day for surveys, more accurate population estimates may be possible than with conventional aerial surveys. ImplicationsConventional aerial surveys may be underestimating animal populations in some habitats. Further studies that directly compare the performance of aerial observers and thermal imaging are required across a range of species and habitats.

An experimental approach to exploring the feasibility of unmanned aerial vehicle and thermal imaging in terrestrial and arboreal mammals research

“…A possible reason for the non-detection of small terrestrial and arboreal mammals in open habitats compared to dense vegetation by thermal imaging is the combined effect of surface reflection from sunlight and thermal radiation from the canopy and ground. Compared to studies by [14], our study shows the same findings, washed-out thermal images in open areas due to high surface reflectance, making it challenging to distinguish animals from their background. The canopy of trees in the surrounding is a significant barrier for thermal sensors to detect animals.…”

Cameras replace human observers in multi‐species aerial counts in Murchison Falls, Uganda

“…It is now possible to test RSO performance with parallel digital camera systems that are inclined at the same angle as RSO-viewing, and image the same strip. Recent cross-comparisons in simultaneous RSO and OCC counting have been conducted for narwhal in Greenland (Monodon monoceros) (Br€ oker et al 2019) and kangaroos in Australia (Lethbridge et al 2019) where thermal image-based estimates of kangaroo density were 30% higher than RSO estimates. In Kenya, an RSObased SRF was run concurrently with high-resolution camera systems in a multi-species count over a large protected area, and it was found that RSOs missed, for example, 60% of giraffe and 66% of the large antelopes (Lamprey et al 2019).…”

Possibility of applying unmanned aerial vehicle and thermal imaging in several canopy cover class for wildlife monitoring – preliminary results

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