This is a male Eastern Bluebird removing a fecal sac from the nest box. If I’m not mistaken, Eastern Bluebirds nestlings will point their posterior in the air to let the parents know that they produced a fecal sac and it needs removing. The parent bird will then remove and fly a long distance to discard it.
A fecal sac is a mucous membrane, usually white or transparent with a dark end surrounding the feces. It makes it easier for parent birds to remove fecal material from the nest. As you can see in my photo, the fecal sac is white for the Eastern Bluebirds.
I read that the nestling creates a fecal sac within seconds of being fed. From my observation of the two baby Eastern Bluebirds in the nest box I have photographed, the parents remove one or two an hour.
How I Got The Shot
I photograph these birds from inside my vehicle. You can see my setup here – My Eastern Bluebird Photography Setup
I had my Fujifilm X-T3 with a Canon EF 100-400 mm f/4.5-5.6L IS II lens attached with a Fringer EF-FX Pro. I have the camera and lens resting on a bean bag draped over the open window of my pickup. I was shooting in aperture priority mode (AV) with a shutter speed of 1/220 of a second at f5.6 and the ISO at 2500. White Balance on auto.
Fecal Sac Facts
- Not all bird species generate them.
- In some birds, the parents will eat the fecal sac. Some believe it is a nutritional benefit to the parents.
- Generally, young birds stop making them shortly before they fledge.
- Removal of fecal material helps enhance nest hygiene, which in turn produces healthy nestlings.
- It also helps decrease the likelihood of predators seeing or smelling it and finding the nest.
Here is a great article from the Audubon: What Are Fecal Sacs? Bird Diapers, Basically