This 2016 video says about itself:
Brood parasitism: American Robin rejects a Cowbird egg
Video credit: Analía V. López, Miri Dainsonm, Mark E. Hauber.
From the Cornell Lab of Ornithology in the USA, 23 August 2018:
How did the bizarre folklore of the “changeling” child first enter European literature? Perhaps an avian reproductive strategy called “brood parasitism” served as inspiration. Brood parasitism is how some birds avoid the work of raising young by laying eggs in the nests of other birds.
In our latest blog post, we explore the origins of the fairy changeling lore by examining some real-life changelings (i.e., cowbirds and cuckoos). Read on for a fanciful new take on folk stories as they relate to nesting biology.