Hummingbirds Measuring Hummingbirds To make precise measurements of the hummimgbird's wing length, tail length, and bill length, Nancy uses a tool called a caliper. It takes just a second or two to open a caliper so the points touch the two ends of the part being measured. Then she can take the caliper away from the bird and read the scale to see how long the body part is. Measuring Hummingbirds Nancy uses a special tool called a caliper to measure the hummingbird's tail and upper beak (called the culmen).   Next: How Much Fat? Facebook Pinterest Twitter © 1997 – 2019 Journey North. All rights reserved.