Estimating animal population size with very high‐resolution satellite imagery

Very high‐resolution (VHR) satellite sensors can be used to estimate the size of animal populations, a critical factor in wildlife management, and acquire animal spatial distributions in an economical, easy, and precise way. We developed a method for satellite population size estimation that includes a noninvasive photogrammetry, from which the animal's average orthographic area is calculated, and an imagery interpretation method that estimates population size based on the ratio of an observed animal population area to the average individual area. As a proof of concept, we used this method to estimate the population size of Whooper Swans (Cygnus cygnus) in a national nature reserve in China. To reduce errors, the reserve was subdivided into regions of interest based on locations of Whooper Swan and background brightness. Estimates from the satellite pixels were compared with manual counts made over 2 years, at 3 locations, and in 3 land‐cover types. Our results showed 1124 Whooper Swans occupied a national nature reserve on 15 February 2013, and the average percent error was 3.16% (SE = 1.37). These results demonstrate that our method produced robust data for population size estimation that were indistinguishable from manual count data. Our method may be used generally to estimate population sizes of visible and gregarious animals that exhibit high contrast relative to their environments and may inform estimations of populations in complex backgrounds. Estimación del Tamaño de las Poblaciones Animales Mediante Imágenes Satelitales de Muy Alta Resolución Resumen Los sensores satelitales de muy alta resolución (VHR) pueden utilizarse para estimar el tamaño de las poblaciones animales, un factor muy importante para el manejo de fauna, y para adquirir las distribuciones espaciales de los animales de una manera económica, sencilla y precisa. Desarrollamos un método para la estimación satelital del tamaño poblacional que incluye fotogrametría no invasiva, a partir de la cual se calcula el área ortogonal promedio del animal, y un método de interpretación de imágenes que estima el tamaño poblacional con base en la proporción del área poblacional observada de un animal con respecto al área individual promedio. Como demostración conceptual, usamos este método para estimar el tamaño poblacional del cisne trompetista (Cygnus cygnus) dentro de una reserva natural nacional en China. Para reducir los errores, subdividimos la reserva en regiones de interés con base en las