Data from: A high-altitude thermal infrared method for estimating moose abundance and demography in Rocky Mountain National Park, USA

Resource managers require accurate estimates of large herbivore abundance
and demography to maintain ecological integrity. Common methods to count
these species, including observations from low-altitude helicopter
flights, may conflict with other protected area management objectives and
struggle to produce precise estimates for more cryptic species. To address
these issues, we evaluated thermal infrared (TIR) assisted counts of
Shiras moose Alces alces shirasi in a temperate montane ecosystem of
Colorado, USA. We binned the 694.7 km2 study area into two strata,
depicting higher and lower moose habitat suitability. Sixty transects
(each 536 m wide by 5 km long) were randomly selected and flown from
fixed-wing aircraft flying at altitudes centered around ~ 610 m (2000 ft)
above ground level (AGL) in July 2019 and again in July 2020. We
determined abundance and demographic information using double-observer
line distance sampling with estimates produced using n-mixture models. The
detection probability of groups on the line, and of individuals within a
group, conditional on the group being observed, was high. Mean moose
density estimates across the study area were consistent from year to year,
with reasonable confidence. We estimated 0.215 moose km-2 (HDI 0.145,
0.286) in 2019 and 0.207 moose km-2 (HDI 0.144, 0.276) in 2020.
Within-stratum estimates varied from year to year, likely an effect of the
definition of suitable habitat and transect classification. Estimated
ratios of bulls per cow and calves per cow fell within expected ranges for
Shiras moose in Colorado but did vary across years. Thermal clutter
created some impact on TIR video quality. Our study indicates that this
approach can reliably estimate moose densities in forested and
topographically complex environments, while maintaining greater aircraft
altitude above ground level when compared with traditional aerial survey
methods. This reduced disturbance to wildlife, impacts on wilderness, and
improved aviator and aircraft passenger safety.