DOI: 10.5061/dryad.gtht76hn6
title: Tracking wildlife energy dynamics with unoccupied aircraft systems and 3-dimensional photogrammetry

description: We present a novel application using unoccupied aircraft systems (UAS;
 drones) for structure-from-motion three-dimensional (3-D) photogrammetry
 of multiple, free-ranging animals simultaneously. Pinnipeds reliably
 haul-out on shore for pupping and breeding each year, accompanied by
 dramatic female-to-pup mass transfer over a short lactation period and
 males lose mass while defending mating territories. This provides a
 tractable study system for validating the use of UAS as a non-invasive
 tool for tracking energy dynamics in wild populations. UAS imagery of grey
 seals (Halichoerus grypus) was collected at Saddle Island, Nova Scotia. A
 multirotor UAS was piloted in 360-degree orbits around relatively dense
 animal aggregations and georeferenced images were used for construction of
 a 3-D point cloud, orthomosaic, and Digital Surface Model for animal
 volumetric measurements. Directly following UAS survey, a subset of adult
 females were hand-measured (morphometrics, blubber depth, n=21 handlings
 [15 were unique animals]) and female-pup pairs were weighed (adult
 females: n=32 [24]; pups: n=33 [23]) to validate that UAS 3-D
 photogrammetric models provided accurate animal volume and mass estimates.
 UAS two-dimensional body length measurements were sensitive to animal
 recumbency and posture. The new UAS 3-D photogrammetric method overcame
 these constraints, and aerial-derived body volume measurements were
 equivalent to those collected from the ground. UAS body volume
 measurements precisely predicted ‘true’ body mass (mean-absolute-error,
 adult female: 8 kg, 2.1% body mass; pup: 4.1 kg, 9.8%), and exhibited a
 stronger relationship with total body mass than with blubber volume. The
 method was applied to 673 free-ranging animals to characterize volume and
 mass dynamics across lactation and breeding for a much larger sample size
 than would be possible using traditional ground methods. Indeed, 1-46
 animals (mean±SE: 9.2±1.2) were modeled concurrently within the focal area
 of a UAS flight. Application of the method also captured significant
 inter-annual variation in body volume/mass dynamics, and female-to-pup
 energy transfer efficiencies were lower when there was low sea-ice extent.
 The UAS 3-D photogrammetric method presented in this study is likely to be
 broadly applicable to other species, and the ability to measure whole
 groups of free-ranging animals at once makes strides towards ‘weighing
 populations’.
description: README_SheroMethodsEcolEvol2021.xlsx contains metadata for each
 of the following datasheets:
 Shero_MEE2021_masses_volumes.csv file contains ground acquired
 mass and animal body volume measurements, as well as the UAS-derived
 volumetric measurements for each animal. Animal posture, terrain, and
 flight characteristics are also provided.
 Shero_MEE2021_larger_area_surveys.csv file contains UAS body
 volume measurements collected from larger area surveys. Note that under
 Age Cagetory, Adult female = "AF", Pup = "P",
 Unaccompanied pup = "UP", and Male = "M".
 Shero_MEE2021_Alta6_flight_specs.csv file contains information on
 flight attributes for the FreeFly Alta 6 multirotor UAS projects used in
 the manuscript. Shero_MEE2021_Morphs_datasheet.csv file
 contains original ground morphometrics measurements that were used to
 calculate animal total body volume using elliptical truncated
 cones.
 Shero_MEE2021_supplemental_DJIPhantom_flightspecs.csv contains
 flight attributes of the DJI Phantom 4 Pro V2 flights used in the
 supplemental materials.
 Shero_MEE2021_supplemental_DJIPhantom_animal_volumes.csv contains
 UAS volumetric measurements of animals imaged with the DJI Phantom Pro V2
 UAS.