An automatic counter for aerial images of aggregations of large birds

Abstract

Capsule: Counts with precision comparable to those of an expert observer can be achieved automatically. Aims: To develop an open-source freeware program that automatically extracts and counts the number of birds in aerial images of dense aggregations. Methods: Software was developed and validated using aerial photographs of Greater Flamingo colonies from France, Turkey and Mauritania. We used a stochastic approach based on object processes. The objects representing flamingos were defined as ellipses, and the software detected these and produced a count. Details of the procedure are provided in electronic supplementary material. The energy is extracted by a birth-and-death algorithm, leading to the total number of birds. Results: This procedure gave counts with precision comparable to manual counts of the aerial photographs by an expert (<5% difference). The procedure does not need any supervision of the extraction by an operator, thus reducing the processing time required to get the estimate of bird numbers in the image from >4h to 20min on average. Conclusion: This open-source freeware should be useful for ornithologists and wildlife managers. © 2011 British Trust for Ornithology.