At first glance, the great tinamou (Tinamus major) seems a candidate for nature’s worst mother.
After a fleeting liaison, this tropical bird abandons her eggs on the forest floor, leaving the father to do all the caretaking while she waltzes off to mate with another male.
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Tinamous are ground-dwelling junglefowl found in the forests of Central and South America. Resembling big brown quails with tiny shrunken heads, they blend into the leaf litter – a logical adaptation, since the forest floor is teeming with predators. What’s puzzling is why such an artfully camouflaged bird lays lurid turquoise eggs – which positively pop in their dark surroundings – and leaves the male alone to protect them.
Birds normally go to great lengths to safeguard their chicks. Some, such as the stork, nest high up, out of reach of most predators. Others, such as the robin, choose subterfuge, secreting their young away in heavily concealed locations. Those that nest on the ground, such as lapwings, generally produce camouflaged eggs and employ both parents as guards.
The female tinamou’s habit of dumping DayGlo eggs in a pathetic nest and leaving dad to do the rest appears to be a recipe for extinction. Yet tinamous are one of the oldest bird families, and the only one in which all 46 species exhibit male-only care. More curious still, these diligent single dads appear to have been cuckolded.
"It defies evolutionary logic"
Studying great tinamous in Costa Rica, scientist Patricia Brennan discovered that 60 per cent of clutches and 24 per cent of chicks were not even sired by the male doing the care. Females were, in fact, mating with multiple partners and dumping eggs in all their nests, creating a muddled paternity that further defies evolutionary logic.
Because standard Darwinian theory predicts that solo-male care should only evolve when males have a high certainty of paternity, Brennan assumed she’d made a mistake. Yet, double-checking her lab work, she found she was right – and wondered how the female was getting away with it.
If paternity is as important to tinamous as it is to evolutionary biologists, one would expect the male to evolve a way of detecting and ejecting foreign eggs. But as Brennan discovered, the male tinamou has no such skills. To do her paternity testing, she had to remove real eggs and replace them with fake ones. The males continued to incubate the bogus clutch regardless. Then, when the chicks hatched in her lab, Brennan would merge them with existing broods in the forest. Again, the males didn’t care. “They didn’t have any kind of recognition mechanism. That says a lot about how important it was for them,” she told me.
That was her lightbulb moment. She set up cameras on the tinamou nests and recorded a whopping 80 per cent of the eggs being eaten by predators, mostly snakes. Brennan realised that the best way for both females and males to maximise their chicks’ survival was to spread their bets across multiple nests. A case, quite literally, of not putting all your eggs in one basket.
This intentional mix-up also explained the eggs’ lurid colour. Their gaudiness is a visual signal to other females to lay their eggs there. Brennan observed that snakes only ate a maximum of three eggs at a time. So, the bigger the brood, the better the chance of some eggs surviving.
Her research, then, not only rescues the great tinamou from being deemed a paradoxical parent, but also demonstrates that the concept of being a good mother can take many forms.
Illustration by Holly Exley
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