Females and males of most bird species are conscientious parents; building nests, incubating eggs, and feeding nestlings and fledglings.

Cuckoos, on the other hand, would be at the top of the list for a "worst parents" award.

A Repeating Cycle

Many cuckoo species are nest parasites, which means they lay their eggs in other species' nests and take off, abandoning their offspring. Often, their eggs have evolved to look similar to the host's eggs so they can't be detected.

When their eggs hatch, the nestlings nudge the host bird's eggs or nestlings out of the nest.

They use their begging skills to fool the host parents into feeding them, and when they grow to adulthood, they repeat the cycle.

How Do They Take Over The Nest?

Scientists have been puzzled by the cuckoo nestling's ability to take over the host's nest.

Early research suggested that their small egg size might enable them to develop faster and get a head start over the host's nestlings. But more recent research has discovered another secret. Female cuckoos also use internal incubation to give their eggs the upper hand.

Cuckoos Are Tricky

Most birds lay their eggs about twenty-four hours after fertilization. Eggs are left at air temperature and occasionally warmed at night until incubation begins. But cuckoos are tricky. Their eggs remain inside the female for an additional twenty-four hours.

Not only that, they stay at a higher temperature than an egg in the nest, so they develop faster. Overall, they have a thirty-one hour advantage over a host egg laid at the same time.

Cuckoos might not be the best parents, but they have evolved an incubation strategy to give their nestlings the best chance to hatch first and wreak havoc in a stranger's nest. It is definitely working.