While we humans sometimes leave food out to feed adult birds, it is up to the mom and dad birds to feed their babies. The babies are voracious, and nature has given them characteristics to make sure that they get fed.
Songbird nestlings have various characteristics that make it easier to get fed. First, they make a gesture called “gaping,” in which they hold their heads up and their mouths wide open. Second, the insides of the mouths of many nestlings are brightly colored to give the parents a “target” for which to aim. The fleshy edges, called “flanges,” of a baby’s beak may be brightly colored too. There is even one bird – a Gouldian finch – that has glow in the dark spots in its mouth.
As children’s author Anna Bird Stewart has said, “Each bird learns first a single word, quite long for a beginner, but says it very plainly, ‘Dinner, Dinner, Dinner.'” Besides gaping, birds have other gestures which prompt parents to feed them. Flamingo chicks practice head bobbing and cheeping; shearwaters nibble their parents bills; herring gulls tap a spot on their parents bills; and young penguins, pelicans, and comorants shove their beaks – and sometimes even their heads – right into their parents’ mouths.
As for a voracious appetite, consider this: many nestlings can easily eat their own weight in food each day. The parent birds devote almost all of their waking hours to feeding the babies. The statistics compiled by the Smithsonian (Smithsonian Q&A Birds, (C) 2006 Harper Collins) are astonishing:
- Hummingbirds feed nestlings once every 20 minutes
- The total length of the worms eaten by one American robin fledgling in a day was calculated to be 14 feet
- A pair of red-breasted grosbeaks fed their young 246 times over 11 hours
- Tree swallows carry home about 8000 insects each day
- Pied flycatchers complete at least 6000 feeding trips to raise their broods