Common Cuckoo - Description

Description

The Common Cuckoo is 32–34 centimetres (13–13 in) long from bill to tail (with a tail of 13–15 centimetres (5.1–5.9 in) and a wingspan of 55–60 centimetres (22–24 in). The legs are short. It is greyish with a slender body and long tail and can be mistaken for a falcon in flight, where the wingbeats are regular. During the breeding season, Common Cuckoos often settle on an open perch with drooped wings and raised tail. There is a rufous colour morph, which occurs occasionally in adult females but more often in juveniles.

All adult males are slate-grey; the grey throat extends well down the bird's breast with a sharp demarcation to the barred underparts. The iris, orbital ring, the base of the bill and feet are yellow. Grey adult females have a pinkish-buff or buff background to the barring and neck sides, and sometimes small rufous spots on the median and greater coverts and the outer webs of the secondary feathers.

Rufous morph adult females have reddish-brown upperparts with dark grey or black bars. The black upperpart bars are narrower than the rufous bars, as opposed to rufous juvenile birds, where the black bars are broader.

Common Cuckoos in their first autumn have variable plumage. Some are have strongly-barred chestnut-brown upperparts, while others are plain grey. Rufous-brown birds have heavily-barred upperparts with some feathers edged with creamy-white. All have whitish edges to the upper wing-coverts and primaries. The secondaries and greater coverts have chestnut bars or spots. In spring, birds hatched in the previous year may retain some barred secondaries and wing-coverts. The most obvious identification features of juvenile Common Cuckoos are the white nape patch and white feather fringes.

Common Cuckoos moult twice a year: a partial moult in summer and a complete moult in winter. Males weigh around 130 grams (4.6 oz) and females 110 grams (3.9 oz). The Common Cuckoo looks very similar to the Oriental Cuckoo, which is slightly shorter-winged on average.

A study using stuffed bird models found that small birds are less likely to approach Common Cuckoos that have barred underparts similar to the Eurasian Sparrowhawk, a predatory bird. Eurasian Reed Warblers were found more aggressive to cuckoos that looked less hawk-like, meaning that the resemblance to the hawk helps the cuckoo to access the nests of potential hosts.

Hosts attack cuckoos more when they see neighbors mobbing cuckoos. The existence of the two plumage morphs in females may be due to frequency-dependent selection if this learning applies only to the morph hosts see neighbors mob. In an experiment with dummy cuckoos of each morph and a sparrowhawk, reed warblers were more likely to attack both cuckoo morphs than the sparrowhawk, and even more likely to mob a certain cuckoo morph when they saw neighbors mobbing that morph, decreasing the reproductive success of that morph and selecting for the less common morph .

The male's call, goo-ko, is usually given from an open perch. During the breeding season the male typically gives this call with intervals of 1–1.5 seconds, in groups of 10–20 with a rest of a few seconds between groups. The female has a loud bubbling call. The song starts as a descending minor third early in the year in April, and the interval gets wider, through a major third to a fourth as the season progresses, and in June the cuckoo "forgets its tune" and may make other calls such as ascending intervals. Also the cuckoo seems to have a form of absolute pitch as it tends to sing in the key of C.