This is a follow-up of sorts to my Throwback Thursday post yesterday. That showed how cramped it was getting inside this nestbox.
After posting it occurred to me that I should post a photo showing how the adults keep the nest clean. While in the nest the young produce fecal sacs. These are droppings encased in a gelatinous sac allowing the adults to carry it out of the nestbox and drop it some distance away.
The young stick their bottoms in the air as a sign to an adult that they’re about to produce one.
Interestingly, when I captioned the slides in 1987 the reference books I used spelled it as faecal sac but the accepted spelling nowadays is fecal.