Cuckoos

Before the word “cuckoo” denoted clocks or craziness it belonged to a bird. Far from crazy, this species could be considered to have a touch of evil genius.

There are 147 species in the family Cuculidae, which also includes roadrunners. Their appearances vary greatly from the tiny mangrove cuckoo of coastal Mexico and the Caribbean, with its blue spotted tail feathers to the safety-orange beak and punk rock crest of the guira cuckoo of central and western South America. They prefer habitats with lots of leafy trees to take cover and blend in with forests, woods, and thickets. They inhabit every country except Antarctica.

The smallest is the little bronze cuckoo of Southeast Asia, New Guinea, and eastern Australia, just six inches long and weighing a bit over a half an ounce. At 10 times that size, the largest is the channel-billed cuckoo, of Australia, New Zealand, New Guinea, and Indonesia, at about two feet long and 1.3 pounds. These regal birds are sometimes called “flying walking sticks” due to their large, curved bills that are sometimes compared to that of a hornbill.

The cuckoo’s diet varies by species but the typical menu is mostly insects, especially the spiny, hairy caterpillars that other birds find irritating to eat. To combat this issue, cuckoos periodically shed their stomach linings. Indian cuckoos and channel-billed cuckoos add fruit to their diet and guira cuckoos also forage for small frogs and mammals. Some cuckoos eat baby birds of other species.

Their calls have a lot of variation as well, but it’s the common cuckoo —found in Europe, most of Asia, and Central to southern Africa— whose call is mimicked by the whimsical German clocks named for the species.

Reproductive behavior

Cuckoo courtship varies among species. Common cuckoos are ready to mate at two years old and both males and females mate with multiple partners. They only make their calls during breeding season, from April to September. Males will spread their wings, fan their tails, and bob their heads, and females respond with a bubbling call.

The lucky ladies of the Diederik cuckoo species get gifts of juicy caterpillars from prospective suitors. Channel-billed cuckoo females will call out to a male, who responds by bringing an insect to her.

Clutch sizes vary among species but the common cuckoo, for example, lays between 12 and 20 eggs a season, which hatch between 11 and 13 days.

Brood parasitism

Cuckoos are well known for laying their eggs in the nests of other birds, called brood parasitism. Some are non-obligate brood parasites, meaning they will put their eggs in nests of the same species or keep them in their own nests. Obligate brood parasites, like the European cuckoo, have lost the ability to make nests and put all their eggs in other birds’ nests.

By pawning their eggs off on other birds, these cuckoos put no energy into brooding or parenting. The cuckoo hatchling may even kick the host bird’s chicks out of the nest. It tricks the host parent into feeding it by sounding like an entire nest full of the host’s offspring. It even gets fed more since it sounds like more chicks. 

Each cuckoo species has preferences about what host species to leave its eggs with.  Females of some cuckoo species have evolved a variety of egg colors to outwit hosts known to throw unfamiliar eggs out of their nests. (Learn more about how cuckoos outsource the care of their offspring.)

Conservation

According to the International Union for the Conservation of Nature, about 77 percent of cuckoo species are of Least Concern. Even so, some regions have seen population declines. In the United Kingdom, for example, the cuckoo population is down by 65 percent, which may have to do with a number of variables including climate-related changes such as droughts brought on by warmer weather that have reduced the number of insects, leaving the cuckoo with less food and less energy to make their trip back to Africa at the end of mating season.

 The critically endangered Sumatran ground cuckoo of the west coast of Sumatra has an unusual light-green-and-black face, dark-green-and-purple feathers, and a haunting call. Its biggest threats are deforestation and becoming bycatch by hunters looking for jungle fowl. However, there are protected areas for this bird and efforts to increase its habitat are underway.