Abstract
Our research presents a proof-of-concept that explores a new and innovative method to identify large animals in aerial imagery with single day image differencing. We acquired two aerial images of eight fenced pastures and conducted a principal component analysis of each image. We then subtracted the first principal component of the two pasture images followed by heuristic thresholding to generate polygons. The number of polygons represented the number of potential cattle (Bos taurus) and horses (Equus caballus) in the pasture. The process was considered semi-automated because we were not able to automate the identification of spatial or spectral thresholding values. Imagery was acquired concurrently with ground counts of animal numbers. Across the eight pastures, 82% of the animals were correctly identified, mean percent commission was 53%, and mean percent omission was 18%. The high commission error was due to small mis-alignments generated from image-to-image registration, misidentified shadows, and grouping behavior of animals. The high probability of correctly identifying animals suggests short time interval image differencing could provide a new technique to enumerate wild ungulates occupying grassland ecosystems, especially in isolated or difficult to access areas. To our knowledge, this was the first attempt to use standard change detection techniques to identify and enumerate large ungulates.
Highlights
IntroductionSources of variation in animal enumeration include observers, habitat or vegetative cover, topography, and animal behavior
Aerial imagery has been used to manually count and estimate population abundances of a diverse array of wildlife species from birds [1,2,3,4] to terrestrial species [5,6] to marine mammals [7,8,9,10,11].Sources of variation in animal enumeration include observers, habitat or vegetative cover, topography, and animal behavior
Manual counting of birds in photographs has resulted in inconsistent counts both within and among observers [1], while counts were less variable for larger bodied terrestrial and marine mammals in homogenous habitats [5,6,7,8,9,10,11,12,13]
Summary
Sources of variation in animal enumeration include observers, habitat or vegetative cover, topography, and animal behavior. Manual counting of birds in photographs has resulted in inconsistent counts both within and among observers [1], while counts were less variable for larger bodied terrestrial and marine mammals in homogenous habitats [5,6,7,8,9,10,11,12,13]. Terrestrial systems with little vegetative structure, such as grasslands or tundra, had fewer features that caused confusion when enumerating individual animals and were usually correlated with lower variation in counts. In the Arctic tundra, which has little vegetative structure and is relatively homogenous, two independent surveyors counted similar numbers of caribou (Rangifer tarandus) [15]
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