Brood parasitism in birds

Kruger National Park | January 2020

It is summer now and many of the birds are getting into their breeding colours. They are preparing to nest and raise new chicks. Males are calling and displaying to attract partners. The sound of the woodland kingfisher is echoing throughout the bushveld, as they attempt to find mates.

In the bird world there are many types of breeding systems including monogamy (where one male mates with one female and they form a “pair bond”, either for life or just for a season), polygamy (where a single bird has numerous partners) and brood parasitism (where a species of bird lays its eggs in the nest of another bird and the host bird then raises the chick/s). There are quite a few species of birds that we see in the Kruger concession that are brood parasites.

It is easy to understand the benefits of being a brood parasite. It is energy consumptive to have to build a nest, lay eggs, feed chicks, protect the chicks from predators etc. The brood parasite basically gets a free ride by laying its eggs in another bird’s nest and getting it to raise and feed the chicks. Rather than wasting energy raising chicks the brood parasite can concentrate more on feeding themselves and laying eggs in various other nests (thus spreading the risk of nest failure).

The host bird is taken advantage of by the brood parasite and often gets the raw end of the deal. As a result, the host birds are particularly wary of the adult brood parasites and will actively chase them away or attack them when they come close to their nests. The adult host birds will often destroy the eggs of the brood parasite if they notice the foreign egg in their nest. Some of the brood parasites have evolved to have eggs which are very similar in size and colour as the host’s in order to fool them into incubating the eggs. In some species of indigobirds and whydahs there is a specific pattern on the inside of the beak that replicates the pattern in the host’s chicks mouths so as to fool the host parents into feeding the foreign chicks.

Often the brood parasite chicks will hatch first and may be slightly larger than the host chicks and thus dominate when it comes to being fed by the ‘parents’. In some cases the brood parasite chick will scoop the host’s eggs or chicks up with their backs and push them out of the nest to reduce competition. In many of the honeyguide species the chick has a sharp hook on the end of its beak initially, with which it kills the hosts chicks, thus reducing competition. Many brood parasites utilise a few different host species, although in some, such as whydahs and indigobirds, the brood parasite is host-specific and only parasitizes a single other species.

In southern Africa there are basically three groups of birds that have evolved to be obligate brood parasites. They are:

  • Old World cuckoos (Cuculidae family)
  • Honeyguides (Indicatoridae family)
  • Indigobirds, whydahs and cuckoo-finches (Viduidae family)

Possibly the best known avian brood parasites are the cuckoos. We are very fortunate to see at least nine different species of cuckoo in the Singita Kruger Concession. These include common cuckoo, African cuckoo, red-chested cuckoo, black cuckoo, great spotted cuckoo, Levaillant’s cuckoo, Jacobin cuckoo, Klaas’s cuckoo and Diderick cuckoo. All of these cuckoos are summer migrants to our area. Most of them feed predominantly on caterpillars and other insects which abound during our rainy season. Most of the cuckoos are highly vocal and we hear them calling throughout the bushveld during our summer months. They produce some of the most characteristic summer sounds in the bush.

Honeyguides are more famous as birds that lead honey-badgers and humans to bees’ nests, hence the family name Indicatoridae. Many people are not aware that they are brood parasites, who usually parasitize hole-nesting birds such as woodpeckers and barbets. In our concession we regularly hear the characteristic “vic-tor”, “vic-tor”, “vict-tor” call of the greater honeyguide or the monotonous, repetitive “klew”, “klew”, “klew” call of the lesser honeyguide.

The adult males of the whydahs and indigobirds both have beautiful summer plumages in order to attract the duller, more cryptically coloured females. The long-tailed paradise whydah and the pin-tailed whydah both grow long tails and display themselves and their beautiful colours to attract the females. Once the male long-tailed paradise whydah has mated with a female (he is usually quite popular with the females, having numerous partners) she will then go and lay her egg/s in the nest of a green-winged pytilia that she is aware of, where the host female has just laid her own clutch. Although the male indigobirds do not grow long tails they do get a beautiful ink-black plumage to attract females. These birds are also host-specific. The village indigobird parasitizes red-billed firefinches, whereas the purple indigobird parasitizes Jameson’s firefinches.

Although the breeding behaviour of brood parasites is very interesting it is not that successful and, therefore, it is estimated that only 1 percent of bird species are obligate brood parasites that require a host to incubate and raise their chicks.

Order of birds:

  • Male long-tailed paradise whydah in full breeding colours.
  • Jacobin cuckoo
  • Great spotted cuckoo
  • Diderick Cuckoo
  • Common Cuckoo
  • Greater honeyguide
  • Lesser honeyguide
  • Male pin-tailed whydah in full breeding plumage
  • Male village indigobird in breeding plumage