Improving the Accuracy of Bird Counts Using Manual and Automated Counts in ImageJ: An Open-Source Image Processing Program

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Abstract

Bird counts estimated ‘by eye’ are subject to high levels of observer variation. Comparison of bird numbers estimated by experienced ornithologists and through manual counting in Image J indicated that observers typically underestimate by more than 30 %, with the median ranging from −13% to −57%. Image J is an open source software package that provides both manual and automated options for counting birds, whether on the ground or in flight. The manual approach has the least preparation time, and will generate accurate counts of 1000 birds in only c. 20 min. This technique is particularly useful for counting birds in breeding colonies, where the complexity of the background in an image will compromise the accuracy of automated approaches. The manual counter provides markers for counting up to eight species simultaneously and is the preferred option for images containing up to 3000 birds. The automated counter is best suited for estimating bird numbers when large groups occur against relatively plain backgrounds. However, the automated counter will not differentiate between species and will typically underestimate the number of birds in an image, as it is object-based and overlapping individuals will count as one bird. Conversely, birds with strongly contrasting plumage patterns will be overestimated.”

Keywords

Variation in observer bird count estimates Object based image analysis (OBIA) ImageJ Open-source image processing software Manual and automated bird counts 
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Notes

Acknowledgements

Thanks are due to Dan Guest, Chris Millican and Jonas Grahn for helping with the thankless task of copy-editing and for providing invaluable comments on the content. I am also grateful to the 35 experienced ornithologists who participated in the observer variation exercise by contributing flock size estimates of the images presented in this chapter: as agreed, these contributors will remain nameless. Finally I would like to thank Ricardo Diaz-Delgado, Manuel Mañez and their colleagues at Estación Biológica de Doñana for giving me the opportunity to accompany their wetland bird counters, both on the ground and in the air: an exercise that rekindled my interest in the subject area and inspired me to write this chapter.

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© Springer International Publishing AG 2017

Authors and Affiliations

  1. 1.Natural Resources WalesCardiffUK

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