Biology
Brood Parasitism and Host Egg Rejection in Reed Warblers
Quick fact
Reed warblers reject foreign eggs about 60-70% of the time, but they make mistakes—occasionally rejecting their own eggs—illustrating the imperfect nature of recognition.
Why this is interesting
A reed warbler returns to its nest to find an egg that looks slightly different from its own. Why does it sometimes toss the egg out, but other times accept it?