1. Variations in counts of seabirds from photographs;MP Harris;Brit Birds,1977
2. Observer variability in estimating numbers: An experiment;RM Erwin;J Field Ornithol,1982
3. Goose counts from aerial photographs using an optical digitizer;DS Gilmer;Wildl Soc Bull,1988
4. An emperor penguin population estimate: the first global, synoptic survey of a species from space;PT Fretwell;PLOS ONE,2012
5. Russell J, Couturier S, Sopuck LG, Ovaska K (1994) Post-calving photo-census of the Rivière George caribou herd in July 1993. The Sixth N Amer Caribou Workshop, Prince George, British Columbia, Canada, 319–330.