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Thermal Drones Found Nearly All Moose in Favourable Winter Weather

Aerial view of a bull moose walking across snow
Conservation · Management

Thermal-camera drones found almost all moose (Alces alces) present in Swedish trials when winter conditions were cold, cloudy and calm. The result shows that drones can be highly effective for estimating moose density, but the researchers also found that weather, forest structure and how animals are distributed in the landscape strongly affect how a survey must be designed.

The study, commissioned by the Swedish Environmental Protection Agency, tested both automated grid flights and manually piloted surveys in three areas in northern and central Sweden. The researchers repeated flights, compared experienced pilots and used GPS-collared moose to check whether animals known to be inside the survey areas were actually detected.

Detection approached 100% in favourable winter weather

Under the favourable winter conditions used in the field trials, detection probability was close to 100%, and all GPS-collared moose within the surveyed plots were found. Manual and automated flights produced very similar results, and drone-based density estimates agreed with independent estimates from other monitoring methods where comparisons were possible.

Required coverage depended on how clustered the moose were

How much land must be surveyed depends on how clustered the moose are. Simulations indicated that covering about 20–30% of an area may be enough for useful density estimates when animals are only moderately aggregated, whereas populations concentrated in fewer places may require coverage of up to 50%. Estimating sex ratio and calves per cow generally requires still larger samples.

Finding a moose was easier than classifying sex and age

Finding a moose was also easier than classifying it. Sex and age could be determined from high-resolution zoom images, but reliable classification required extra flight time, several viewing angles and experienced observers. Sunlight creates another problem: warmed rocks can resemble animals in thermal images, while heated treetops can mask the heat signature of a moose below.

The authors therefore recommend repeated surveys in some plots when conditions are less favourable, so detection probability can be estimated rather than assuming every animal has been found. Battery endurance and aviation rules that restrict flights beyond the pilot’s visual line of sight also limit how efficiently large areas can be covered.

The report presents drones as a potential complement to Sweden’s existing moose-monitoring methods, not a replacement for them. Before drone data can be used routinely in management, the researchers call for standardised protocols, training and quality assurance, together with further tests under different weather, seasons and forest conditions.

Sources and image credit

  1. Inventering av älg med drönare: Utveckling av metodik för uppskattning av täthet, könskvot och reproduktion
  2. Drones have potential for moose surveys – but weather can be a limiting factor

Image: U.S. National Park Service — aerial view of a male moose (Alces alces) walking across snow in Lake Clark National Park and Preserve, Alaska, 2 December 2010; NPGallery/Wikimedia Commons. Representative aerial winter image, not from the Swedish drone study. · Public domain · Source

About this content: This story was produced with AI assistance within an editorial workflow developed by Wildlife Vagabond. Editorial responsibility remains with Wildlife Vagabond.How AI is used

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