The darker bird pictured above belongs to a family of trickster birds known as the
cuckoo. The common cuckoo is notorious for creeping into other birds' nests and laying their eggs, leaving the hosts to raise the chick as their own. This mechanism is known as
brood parasitism, and it is quite common in the animal kingdom. However, not all cuckoos are dead-beat parents, many do raise their own young. The cuckoo birds that do use this mechanism are obligate brood parasites, meaning that they only reproduce in this fashion.
The best-known example is the
European common cuckoo (shown above). The shells of the eggs of brood-parasites are usually thick. They have two distinct layers with an outer chalky layer that is believed to provide resistan ...
