When you think of birds raising their young, you probably think of something like this: parents build a nest, they lay their eggs, the eggs hatch, chicks are fed until they grow up and they finally leave their parents to make their own way in the world.
Young Grosbeak Weaver (Amblyospiza albifrons) in its nest, patiently waiting for its parents to return with food
That's true for most birds, but there are some that don't follow this established order. They choose to take a shortcut. They don't want to waste time and energy raising their chicks, so they instead trick other birds into doing it for them! This rather shifty behavior is called brood parasitism.
A number of birds found in Kenya are brood parasites. Two main groups are the most infamous: cuckoos (belonging to the Cuculidae family) and honeyguides (Indicatoridae family). Not all members of the Cuculidae are brood parasites though. Coucals belong to this family but they raise their own chicks.
White-browed Coucal (Centropus superciliosus) seemingly collecting material for its nest
Generally, this is how brood parasites breed: the pregnant female searches for a 'host' bird of similar size that is currently nesting (though the host can sometimes be ridiculously smaller!), she sneaks to the nest when the host is not aware and quickly lays her egg among the host's eggs. If the parasite's egg hatches first, the chick may push out the host's eggs to eliminate competition. Even when the host's eggs hatch first, the parasitic chick will often outcompete them for food from the parents and they will eventually die.
The host parents' instincts to raise any chick that hatches in their nest is so strong that they don't seem to tell the difference between their own chicks and the 'imposter', even when the foreign chick is bigger than the parents themselves! The most ridiculous size difference I have ever seen was a Variable Sunbird (Cinnyris venustus) working very hard to feed a young Klaas's Cuckoo (Chrysococcyx klaas) that was nearly twice its size!
A juvenile Klaas's Cuckoo in Nairobi. It has never met its parents. As an adult, it will rely purely on instinct to take care of itself since it will have never learned anything from its parents.
Greater Honeyguide (Indicator indicator) female in Mwingi National Reserve. This species is best known for its charming behavior of leading people to bee's nests for honey (which is true, by the way), hence its name. Fewer people however know the less charming part of its character - that it is a brood parasite.
So why do brood parasites do what they do? Well, it's quite simple. It's about minimizing effort while maximizing gains. They are trying to spread their genes as widely as possible while using as little energy as possible to do so. It's all about survival and reproduction. One female may lay 4 eggs, for example, but it will lay them in 4 different nests just in case one or two of the nests fail. This ensures that at least some of its offspring survive.
Diederik Cuckoo (Chrysococcyx caprius) female - Nairobi National Park. Some brood parasites only target one specific host species and their distribution will mirror that of their host. Others are less choosy.
We can judge these birds from our human perspective as much as we want, but if you really think about it, it's a pretty smart way of making sure that at least some of your children survive. Remember that this is the wild, where chances of reaching adulthood are rarely high for a young animal. In nature, there is no right or wrong. There is only what works and what doesn't. It's natural selection. Right and wrong are subjective. They are human judgments. In the case of brood parasites, their strategy is what works. It maximizes their chances of passing on their genes (their bloodline) to the next generation. It is success.
Scaly-throated Honeyguide (Indicator variegatus) - Loita Hills
Breeding strategies among birds are as diverse as the birds themselves. It is part of what makes birds so fascinating. Next time you see birds at their nest or showing some signs of breeding, take time to observe them. You may witness something that amazes you.
Various cuckoos, honeyguides and other brood parasitic birds can be found throughout Kenya. Feel free to get in touch if you need help finding a professional guide who knows Kenya's birds and can interpret such interesting behavior for you.
Jacobin Cuckoo, or Black-and-white Cuckoo (Clamator jacobinus) - Nairobi National Park
And while out enjoying the antics of Kenya's birds, do submit your records to the Kenya Bird Map project to help map their distribution throughout the country.
To learn more about the birds of Kenya and other parts of Africa, have a look at these book recommendations.