The use of digital photography in systematics

Systematic problems often depend on whether individuals or taxa differ in colour. Recent advances in digital camera technology have made digital photography an attractive method for quickly and easily obtaining objective colour measurements. The present study explores some potential applications for the use of digital photography in systematics. Using an affordable camera apparatus that can take both visible and ultraviolet images, it is found that colour measurements of bird plumage patches are highly repeatable. Calibrated digital images were used to quantify visible and ultraviolet colour in several avian examples, and issues addressed included characterizing the extent of invisible ultraviolet patches, quantifying the degree of colour difference among patches, and testing for cryptic sexual dichromatism. Because the spatial relationships among colours are preserved, colour patterns can be quantified from digital images. As an example, the amount of head spotting is measured along a geographical transect to characterize the shape of a phenotypic cline between two taxa. Another potentially powerful application of digital photography is for species delimitation. Digital images were used to assess colour differences between two putative taxa. Patch measurements were plotted in three-dimensional colour space to determine whether patch colour overlapped between taxa. Four of the five colour patches that were originally described as distinguishing taxa were non-overlapping, and so the taxa were determined to be diagnosable. Digital photography thus provides a potentially powerful method for addressing systematic problems.(c) 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110, 1-13.