Stress Bars

Cleaning the raptor mews may be a dirty job, but it can lead to some interesting discoveries. Under a pile of shredded newspaper, I found this feather from Carson the Red-tailed Hawk. The central shaft forms a slight S-curve, telling me this came from Carson's alula, a bird's "thumb." 

I noticed faint lines along the feather vane like frets on a guitar's fingerboard. Known as stress bars, these lines are weak spots in the feather. They form if the bird undergoes heightened stress as the feather grows. It might be physical stress like starvation or psychological stress like escaping a predator. For Carson, I believe these stress bars are caused by her permanent wing injury affecting feather growth.