Summary
Cuckoos lay eggs in other birds' nests, driving an evolutionary arms race of mimicry and detection.
In depth
Cuckoos mimic host eggs; hosts evolve egg rejection; cuckoos evolve better mimicry. Some chicks beg with exaggerated calls mimicking a brood. Honeyguide birds, cowbirds and some fish also parasitise.
Hosts respond with egg rejection, nest abandonment or chick discrimination. Parasites respond with better mimicry, faster laying and tricks such as eggshell thickness. It is a model of coevolution.
Example: some host species evolved distinctive egg patterns that make forgeries easier to spot.
Brood parasites lay eggs in other birds' nests and leave the hosts to raise the young. Obligate parasites include cuckoos, cowbirds and honeyguides; the parasitic chick often hatches early, ejects host eggs or outcompetes host chicks.
Hosts evolve defences such as rejecting odd eggs, desertion or recognising intruders, and parasites respond with better egg mimicry and chick begging signals, a coevolutionary arms race. Egg colours in some hosts become more variable to make forgery harder.
Example: common cuckoo eggs mimic the colour and pattern of reed warbler eggs.
Frequently asked questions
What is Brood Parasitism?
Cuckoos lay eggs in other birds' nests, driving an evolutionary arms race of mimicry and detection.
Which area of biology covers Brood Parasitism, and how advanced is it?
Brood Parasitism is one of the 53 topics in Animal Behaviour. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Play Behaviour, Predator-Prey Arms Races, Animal Cognition Experiments.
Why does Brood Parasitism matter?
It is a classic example of coevolution and of how learning (imprinting on eggs) shapes defences.
Can you give an example of Brood Parasitism?
Reed warblers reject eggs that differ from theirs.
What should I learn before Brood Parasitism?
Work through the Beginner topics in Animal Behaviour first, such as Animal Behaviour, Innate Behaviour, Learned Behaviour, then return to Brood Parasitism. Advanced topics assume the Intermediate vocabulary.
What topics are related to Brood Parasitism?
The closest topics to Brood Parasitism are Play Behaviour, Predator-Prey Arms Races, Animal Cognition Experiments, Innate Behaviour. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Brood Parasitism?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Brood Parasitism. To practise the whole of Animal Behaviour, use the Animal Behaviour quiz.
How is Brood Parasitism different from Play Behaviour?
Brood Parasitism: Cuckoos lay eggs in other birds' nests, driving an evolutionary arms race of mimicry and detection. Play Behaviour: Seemingly purposeless activity in young animals that develops skills and social bonds. Read both side by side and note what each one explains.
How should I study Brood Parasitism step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Play Behaviour and explain the difference aloud. Finally, take the Animal Behaviour quiz and come back to this page for any question you miss.