Songbirds evict some chicks, sacrificing them to give others a better chance of survival

A radio-tagged fledgling common yellowthroat is shown here.

(CNN)You may admire the birds in your garden for their commitment to their young -- endlessly catching bugs and delivering them back to the brood of chicks in their nest.

But researchers from the University of Illinois have uncovered a darker side to songbird parenting. They have found many species deliberately evict their young chicks -- before they are ready to fly.
The study, led by the university's College of Agricultural, Consumer and Environmental Sciences, looked into the behavior of 18 songbird species in various habitats across the United States and found they all forced some of their chicks out of the nest.
    The scientists assessed a number of papers stretching back as far as 2004 to draw their conclusion, researching the behavior of species including the Acadian flycatcher, brown-headed cowbird, indigo bunting and worm-eating warbler.
      The paper, published in the Proceedings of the National Academy of Sciences, found all of the species studied "manipulated" some of their offspring into leaving the nest early.
      They do this, the researchers believe, by decreasing the amount of food they give them, to force them out with hunger, and by communicating with them directly to encourage them to leave.