Baby Birds’ Built-in Diapers

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Baby birds in their nests can be a darling sight to behold. But like all babies, chicks produce a lot of poop. And if they're babies of passerine, or "perching", birds, they'll typically spend lots of time in the nest—being rather underdeveloped at birth—crowded and confined with siblings. This means lots of time spent huddling, begging for food, growing prodigiously and, yes, pooping.

So how do birds keep their nests from filling up with waste? An ingenious solution known as the fecal sac. Like a built-in diaper dispenser, the digestive tract of most passerine chicks produces a mucous membrane at its terminus to envelop excreta. These sacs, like the disposable diapers humans find so convenient, make for easy clean-up by the parents. The process is unsurprisingly straightforward: Baby bird is fed, promptly excretes a sac for removal; parent flies off with said sac to dispose far from nest. As the old (sanitized) saw goes, "Don't poop where you procreate." Distant disposal has some very practical benefits: poop smells and breeds disease, and its presence near a nest could alert potential predators to the chicks' whereabouts.

This Chestnut-backed Chickadee is seen removing a fecal sac from its cavity nest in a Big-leaf Maple.