Gaelic name: Còrcach, Chuthag
Conservation Status: Red
A familiar, summer visitor to the UK and although falling numbers are of concern in the south, still widespread in Scotland, arriving from Africa late April and departing after breeding. Its familiar coo-koo call from the male will serenade us during May and June in particular. Females make a bubbling trill sound. There are currently an estimated 18,000 breeding pairs spread across the UK.
Understanding the decline of the Common Cuckoo
Identification
A medium size bird, length 32 – 36 cm, with short legs and weighing around 110 gm. The male is ash grey on head, back and breast, with sparrow hawk style barring on the belly. Females usually have a similar pattern, but with a rusty tint and possibly barring spreading up the breast. Juveniles will be distinguished by a darker brownish colouring above and a white spot on the nape is a definite indicator of immaturity.
Flight pattern is low, with short wingbeats mainly below horizontal plane and absence of gliding.
Food
Cuckoos eat invertebrates. Hairy caterpillars are a favourite, which other birds avoid. Lack of adequate food source in farmland areas of southern Britain may be a pointer towards dwindling populations.
Habitat
Cuckoos can be found across many terrains, but especially heaths, woodland, moorland, marshland and farmland, although the latter on a reducing scale. Taking into account its shy nature, this bird avoids populated areas.
Breeding
Seen by many as a tyrant, the cuckoo foregoes the tasks of nest building and parenting, by following a parasitic regime. Constantly watching for an opportunity, the female will lay one egg in the nest of an unsuspecting future host. This is where things get really interesting, as the cuckoo possesses the ability to mimic the eggs in the recipient nest. Numerous races exist within this species, each laying an egg which matches those of their favourite target foster parent. In the UK, these are more commonly Meadow Pipits, Reed Warblers and Dunnocks, varying across terrains. These are solitary birds and the female is not choosy over partners, laying up to 25 eggs each season.
Carefully monitoring target nests, the female will stealthily glide to a temporarily vacated nest, quickly remove one egg to keep the numbers identical, probably gobbled up, then lay her own egg and depart to a safe distance, all of this within the space of around 10 seconds. Around 11 days later, the infant hatches and instinctively heaves eggs or chicks from the nest, heaving upwards with its shoulders. Baby cuckoo has another trick up its sleeve, to fool the foster parents into believing they have a full nest of chicks to feed – its own requirement for food being as large as maybe half a dozen pipits! It has the ability to produce rapid feeding calls, telling the adults there are many mouths to be filled. Another 20 days pass by and the chick is now considerably larger than its ‘parents’ and ready to
fledge the nest. It will remain close by though, being fed for another 2 or 3 weeks before becoming self dependant. The juvenile bird will not know its real parents – who will by now be on the southerly migration route, this being late June or early July. The young cuckoo will not depart UK until much later, most likely in August.
Migration
Satellite tracking by the BTO for more than a decade of adults tagged with miniature transmitters, has now revealed very useful information on migration routes followed by these birds on their long journeys to and from Central Africa. Results from this research show a correlation between routes and declining / stable populations. Cuckoos from Scotland, where numbers are stable or increasing follow the easterly path through Italy, whereas the westerly route through Spain relates to territories further south in UK. These journeys are undertaken in stages, with breaks in both southerly and northerly directions to re-fuel for their long passages. Crossing the Sahara desert without a break presents arduous challenges and can result in significant mortality rates, particularly amongst juveniles on their first unguided attempt.
More interesting reading can be found here on migration movements and populations:
Useful articles:
Guide to cuckoos: where to see in Britain and why the species is in decline
Sad countryside silence as the cuckoo moves north
Thanks to group members David Cuthbertson, Penny Gardner, Stephen Kirkup and Hedley Wright for use of their photos, which is much appreciated.
John Wright – May 2024
