How an Eight-Sided ‘Egg’ Ended Up in a Robin’s Nest - The New York Times
https://www.nytimes.com/2021/01/29/science/robin-eggs-nest.htmlThe limits of egg recognition: testing acceptance thresholds of American robins in response to decreasingly egg-shaped objects in the nest
https://royalsocietypublishing.org/doi/10.1098/rsos.201615