It prompts the parent bird to feed them.
to eat, or to sing, or to vomit into the mouths of their children
They open their mouths on land, and led birds eat the food on their teeth. Hope this helps.
they open their mouths to suck in food.
for food
They open their mouths and swallow it.
Crocodiles clean their teeth by opening their mouths wide and allowing small birds called "crocodile birds" to pick food bits and debris from between their teeth. This cleaning symbiosis benefits both species as the birds get a meal and the crocodiles get their teeth cleaned.
They open their mouths, grab the food, and swallow !
Innate.
they open their mouths, bite some food, chew, then swallow
They normally lie with their mouths partly open, and the local birds pick off any bits of flesh from the teeth.
Crocodile and Hippos because when they open their mouths the birds will peck all off the bacteria and leftovers.
Fish open their mouths to breathe by taking in oxygen-rich water, to eat by capturing prey or scavenging for food, and to communicate with other fish through displays of aggression or courtship.