Nests look like safe havens for baby birds but if they’re not kept clean they can quickly become infested with pathogens and parasites, or their smell can attract predators. For songbirds it’s especially important to keep their nests clean. Fortunately their bodies have evolved to make this easy.
In the photo above, a western bluebird is taking out the garbage after visiting his nest. In his beak is a fecal sac, a package of white mucous membrane surrounding the feces of one of his nestlings. Every nestling produces a fecal sac shortly after eating. The packaging makes it easy to keep the nest clean.
What the parents do with the fecal sacs depends on the species. Most drop them far away from the nest but some species, such as American robins, consume the fecal sacs while the nestlings are quite young and carry the sacs away when the nestlings are older.
Just before songbirds fledge their bodies switch from producing fecal sacs to defecating wet feces over the edge of the nest. Robins’ nests don’t have whitewash beneath them until you can see the youngsters above the nest rim. By the time they are messy, baby robins are almost out of there.
Birds of prey aren’t as fastidious. If you watch peregrine and bald eagle nestcams, you’ll see two differences in their nest sanitation:
- Raptor nestlings don’t produce fecal sacs. Instead they back up to the edge and aim wet feces away from the nest.
- As the nestlings age the parents become lazy housekeepers, often leaving food debris at the nest as a self serve snack for the young.
Birds of prey aren’t worried that predators will smell their nests. That’s why they don’t always take out the garbage.
(photo from Wikimedia Commons; click on the caption to see the original)