Animals are amazing actors with the ability to mask injuries and illness. They want to hide any weakness from potential predators or competitors, while still finding their basic needs to survive. Raptors will keep hunting for food even with extreme injuries. When our Great Horned Owl, Theo, was rescued, he appeared to be well fed. The rehabilitators believed he was actually running down mice despite having a broken wing. Since their behaviors rarely show signs of illness, their weight is often the first sign of a problem. We take daily or weekly weights to track our birds’ health. The key is knowing what is normal for each bird.
I chart each bird’s weight to keep an eye on patterns. Aldo’s chart, for example, shows daily fluctuations and seasonal changes. His weight last summer hovered around 108 grams (3.8 oz) and increased in November. The higher weight gives him a little extra buffer against cold temperatures through the winter. As spring approaches, he has begun shedding weight in preparation for breeding season and warmer weather. With a baseline of these normal weight patterns, I can identify abnormalities and keep him at healthy weight.