Use of a gel documentation system to measure feather growth bars

Feather growth bar widths have become a standard index of nutritional condition in ornithological research. Traditional techniques of measuring these bars are difficult and slow because the bars are often hard to see. We present a fast and repeatable method of visualizing and measuring growth bars using a gel documentation system from Alpha-Innotech Corporation. This system takes digital photos of objects in a low light chamber. These photos can then be enhanced and measured on a computer. We show that this system can be used to quickly obtain repeatable measurements of growth bars that are highly correlated with those obtained using traditional methods. The high repeatability and low inter-observer variability of our results also validates more traditional methods of ptilochronology.