Web databases of feather photographs are useful tools for avian morphometry studies

Abstract

1. Wing area, wing loading and aspect ratio are key variables for studies of avian comparative ecology, despite the complexity of measuring wing characteristics in living and museum specimens. The systematic databases of feather photographs available on the internet may offer an alternative way of obtaining such morphometric data. Here we evaluate whether measurements of scanned feathers from web photo databases may offer reliable estimates of avian morphometry. 2. Published data on wing area was obtained for 317 bird species and feather measurements from web photo databases for 225 of them. A variable termed ‘lift generation area’, a proxy for wing area, was calculated for each species on the basis of the mean length of the five distal secondary feathers and wingspan data from literature. The fit between this proposed variable and data extracted from the literature was examined by correlation, employing linear regression to explore the lack of fit among species. 3. ‘Lift generation area’ proved to be highly informative as a proxy for wing area for the study species as a whole (R2>0.98). Discrepancies observed between species were strongly negatively associated with the size of the original sample used to calculate wing area (P=0.001) and, to a lesser extent, with bird size (P=0.023), but not with aspect ratio. It was also found that the mean value of the mismatch between ‘lift generation area’ and wing area (13.1%) among the study species as a whole was of similar magnitude to that found between sources of bibliographical wing area data for the 64 species for which two published estimates of this variable were available (15.3%). 4. We conclude that measurements made from feather photo databases are reliable for use in studies of avian comparative ecology, enabling the inclusion of biomechanical parameters of many more species than featured at present.