An unexpected encounter with a juvenile diderick (formerly diederik) cuckoo in our garden prompted me to find out a bit more about brood parasites and diderick cuckoos in particular.

A few weeks ago, hearing a baby bird calling incessantly from a small tree in our garden, I went outside to see if I could find it. Eventually I spotted a young cuckoo partially concealed in the foliage.

I only had an enticing glimpse of its beautiful markings – streaks, dots and barring – and of its coppery head and splashes of iridescent green and copper on its back and wings before it suddenly flew off and up high into a tall tree, where it perched and resumed its plaintiff repetitive begging call.

Screwing my eyes up against the light I could see the orange bill of the cuckoo and its pale underside marked with streaks and dots

After a while the cuckoo flew down and around the corner of the house. I slowly crept around the corner in the hope that it had landed lower down. Sure enough, I soon heard it resume its begging call. Now I was the one concealed in some vegetation, and peeping past some bare branches I got a clearer view of the young cuckoo.

The cuckoo did not show if it was aware of my presence. It seemed focussed on demanding to be fed by whoever was fostering it

In preceding weeks, I had heard both Klaas’s cuckoos (Chrysococcyx klaas) and diderick Cuckoos (Chrysococcyx caprius) calling in the neighbourhood, and even seen an adult male Klaas’s cuckoo in our garden. The adult males of both these cuckoos are predominantly iridescent or metallic green offset by bright white in colour, and I guessed that this juvenile was likely one or other of these.   

The impatient juvenile cuckoo adopted an assertive posture while begging – revealing the strength of character required to be a brood parasite. At breeding time, adult female cuckoos require perseverance, cunning and courage when seeking to invade the nests of unwilling hosts

The young cuckoo was more than a little impatient, continually chirping and looking around, demanding to be fed. I stayed as concealed as possible, but looking up I saw a male Cape sparrow (Passer melanurus) watching me warily.

Even though I was partially concealed by branches, the male Cape sparrow watching me from on high

The cuckoo continued apparently to ignore me as it looked around and up towards the sparrow, fluttering its wings as it emitted its high-pitched begging call

I was starting to put two and two together as it dawned on me that the cuckoo was likely begging from the sparrow! I had not known that diderick cuckoos parasitise Cape sparrows, but now that was a consideration, I started to worry that my presence was deterring the sparrow from attending to the cuckoo. But after a short time away, the sparrow returned. Throwing caution to the winds, it flew straight down to the juvenile cuckoo and proceeded to feed the hungry baby.

The male Cape sparrow feeding the juvenile cuckoo that is quite a bit larger than its foster dad

Later on, when I looked up cuckoos and their hosts, I learnt that the third most common species to host diderick cuckoos is the Cape sparrow. The Klaas’s cuckoo does not use Cape sparrows as a host. Its primary hosts are batises, small warblers and sunbirds.

As I do not have a decent photo of adult diderick cuckoos, I took a snapshot of the illustrations showing diderick cuckoos on p.275 of the Roberts Bird Guide

Of the 24 species known to host diderick cuckoos, the four primary host species occur in our area. The most common diderick cuckoo host species, the southern red bishop (Euplectes orix), I have seen nesting colonially in reed beds down at the local river. The second most common host is the southern masked weaver (Ploceus velatus), with the Cape sparrow being the third, and the far less favoured Cape weaver (Ploceus capensis) is in 4th place.

After a brief feeding session, the male sparrow flew off. The juvenile looked in my direction, and resumed its exasperated begging call

Brood parasitism is an interesting phenomenon where parasitic parents manage to get host parents to raise the parasite’s young as their own. The strategy is for the parasitic female to lay an egg in the nest of the host; an unaware host will brood the egg and raise the hatchling as its own.

There are some species of birds that parasitise birds within the same species – for example, a species of grebe and two species of swallow. But usually, when we think of birds that are brood parasites, we think of birds that never make their own nests and only parasitise birds of other species. They are known as obligate, interspecific parasites, and remarkably such behaviour evolved independently (a phenomenon termed convergent evolution) in at least five separate groups of birds.

These five groups are cuckoos, cowbirds, honeyguides, viduids (whydahs and indigo birds) and ducks, although only a single species of duck (in South America). Worldwide there are about 100 species of birds that are obligate, interspecific brood parasites, comprising about 1% of the total number of bird species.

The cuckoo seemed perplexed, before deciding to fly off and return to near the shrub where I had first discovered it

About one third of species of cuckoos are brood parasites. Fascinatingly, given the diversity of hosts known to be parasitised by different species of cuckoo, there is evidence that some species, including common cuckoos and diderick cuckoos, have evolved host-specific strains (races), termed gentes (singular gens). Females in a specific gens lay eggs that tend to match the host’s eggs in appearance. Female cuckoos when they are breeding also tend to select the species that reared them as targets. In other words, they will lay their eggs in the nests of the same species that fostered them.

The juvenile cuckoo that I was following returned to the place where I had first seen it. I hid in a doorway and witnessed the hardworking male Cape sparrow return to feed the noisily demanding cuckoo. Strangely, there was no female sparrow in evidence.

After feeding the cuckoo, the sparrow descended to the ground below foraging for food. The cuckoo looked on impatiently from above.

I crept out from the doorway and hid behind a shrub to try to see what the sparrow was gathering. It appeared to be gathering fallen seeds, possibly from the fruiting tree fuschia (Halleria lucida) beneath which it was foraging.

The cuckoo, doing a bird version of a scowl, quivered its wings in anticipation if it thought the sparrow was about to return to feed it.

When the sparrow returned, it wasted no time in feeding the cuckoo who opened its bill wide to receive the food from the dutiful sparrow.

The sparrow paused to give the cuckoo a chance to swallow all the food, which I took to be seeds, as that appeared to be what the sparrow was picking up from the ground. It is possible that the sparrow dehusked the seeds it had collected before feeding the cuckoo.

Cape sparrows’ food includes a variety of seeds, fruits and flower buds, several species of insects, and also caterpillars, any of which they may feed to their own young or to diderick cuckoo chicks that they are raising. Diderick cuckoo adults eat mainly caterpillars, but also eat several species of insect.

As soon as the food was swallowed, the cuckoo gaped widely asking for more.

The sparrow would oblige as soon as he could, sometimes feeding two or even three times from one foraging trip.

The cuckoo, however, was never satisfied.

Even when the cuckoo retreated further into the shrubbery, the harried sparrow would return repeatedly to feed its large foster child.

This is the last photo I took of cuckoo still managing to look dissatisfied, despite the sparrow’s hard work. As it has so much green in its plumage, it appears to be an older juvenile and so soon it will be foraging for its own food and the sparrow can take a well-deserved break.

Sources:

African Cuckoos: Research on Brood Parasites and Other Curious African Birds. [n.d.] African and Diederick Cuckoos. https://www.africancuckoos.com/study-systems/african-and-diederik-cuckoos/

Biodiversity Explorer: The Web of Life in Southern Africa. [n.d.] Chrysococcyx caprius (Diderick cuckoo). Iziko Museums of South Africa. http://www.biodiversityexplorer.info/birds/cuculidae/chrysococcyx_caprius.htm

Bouglouan, Nicole. [n.d.]Diederik Cuckoo. Chrysococcyx caprius. https://www.oiseaux-birds.com/card-diederik-cuckoo.html

Chittenden, Hugh, Davies, Greg & Weiersbye, Ingrid. 2016. Roberts Bird Guide: Illustrating nearly 1,000 Species in Southern Africa (2nd edition). Cape Town: Jacana.

Phillipsen, Ivan. 2020. What is brood parasitism in birds? The Science of Birds.

https://www.scienceofbirds.com/blog/what-is-brood-parasitism-in-birds

Roberts VII Multimedia Birds of Southern Africa: PC Edition.  1997-2016 Southern African Birding. For details go to http://www.sabirding.co.za/roberts7/portal.html

Posted by Carol