Photography as a tool for avian morphometric measurements

Abstract

Accurate morphometric measurements of birds are frequently needed in studies to provide an index of body size. However, obtaining these measurements in the field can be challenging and inter-observer repeatability of taking these measurements using calipers has been questioned in the literature. Here we present a method for measuring tarsus length and bill length, width and depth using digital photography with open source software (ImageJ), and we compare the repeatability and handling time of the digital measurements with those traditionally made using calipers. The digital method was more or equally repeatable than manual measurements of bill and tarsus and its repeatability was independent of measurement length, making it especially suited to making shorter measurements. While digital and manual measures were highly correlated for all body measures, the digital method produced slightly higher measurements in all cases meaning digital and manual measurements may not be directly comparable. Morphometric measurements made from digital photographs were possible with a significantly shorter bird handling time, can be completed by less experienced fieldworkers, and create a permanent record that can be later verified, making them a useful alternative to traditional manual measurements of unfeathered skeletal body parts which can be clearly visualized in photographs.