Cuckoos are masters of deception. When it comes to raising their young, these birds don’t need to build a nest, protect their eggs or feed their offspring. Instead, female cuckoos pass these roles onto unsuspecting victims.
Cuckoos are brood parasites, meaning they don’t raise their own young. They lay their eggs in the nests of other bird species, according to the Max Planck Society in Germany, tricking other birds into thinking the cuckoo eggs are theirs. Some of the main targets for cuckoos include dunnocks (Prunella modularis), meadow pipits (Anthus pratensis) and reed warblers (Acrocephalus scirpaceus), researchers reported in 2009 in the journal Bird Study.
There are 150 species of cuckoos listed in the IOC World Bird List, all of which belong to the Cuculidae family. They are medium-size birds averaging 13 inches (33 centimeters) long and weighing about 3.7 to 4.5 ounces (105 to 130 grams). They often have gray or brown backs and barred bellies, and have long tails, according to the Woodland Trust.
When a cuckoo hatches and begins to grow in a host’s nest, it can look obvious to an onlooker that the cuckoo is not the same species as its foster parent. Sometimes, a young cuckoo is six times bigger than the host parent, but it continues to receive food, according to research published in 2018 in the Proceedings of the Royal Society B.
The cuckoo imposter is usually the only hatchling that a host parent has to care for. This is because the young cuckoo gets rid of all the other eggs in the nest. It will usually hatch before the other eggs, after around 11 days in the nest. Then, it will carry the other eggs on its back, one by one, and throw them over the edge of the nest, according to BBC Wildlife.
A cuckoo’s new, non-biological parent will continue to treat it as one of its own chicks. After 20 days, the cuckoo will leave the nest but will still receive food from its former host, according to the Woodland Trust.
Cuckoos sometimes lay their eggs outside of the hosts’ nests, according to a 2019 journal article published by The Royal Society. If an egg looks similar to the host’s eggs, the host can retrieve the seemingly misplaced egg and place it in the nest itself.
Sometimes, a cuckoo chick will be rejected by its host after hatching, because of the cost of raising the cuckoo. An example of this is when the cuckoo is much larger than its unsuspecting new parent, according to research published in the Journal of Zoology in 2011. Feeding the cuckoo will use up much more of the host bird’s energy. If the chick’s demands are much higher than the host would expect from its own species, the cuckoo can be abandoned at this later stage.
Around the time of laying their eggs, female cuckoos have been known to distract the host birds by producing a noise similar to Eurasian sparrowhawks (Accipiter nisus), according to an article published in the Journal of Experimental Biology in 2017. This is to alert the birds to potential dange, distracting them from the nest. This gives the cuckoo enough time to lay her eggs and to make her escape, unspotted.