How owls became the super predators of the night – 03/09/2024 – Reinaldo José Lopes

You don’t have to be superstitious to feel that there is something ghostly about contact with an owl. The few encounters I have had with them to date have almost always been decidedly spectral – a figure that appears and disappears with equal speed in our peripheral vision; an almost magically silent swoop to snatch a field mouse from the ground, followed by a takeoff into the night.

However, as that cheesy propaganda from the beginning of this century said, none of this is sorcery: it is pure evolutionary biology. The last decades of research have revealed many of the secrets that transformed owls into such elegant and relentless nocturnal hunters (mentally underline the “most” in the last sentence: not all of them are as nocturnal as we usually imagine). This column details some of these capabilities.

Firstly, consider that the animals’ almost inaudible flight is a biomechanical feat produced by multiple interconnected systems. Part of the secret is the relatively large size of their wings in relation to their bodies, which allows them to fly slowly and gracefully. But there is more.

The entire surface of owl wings is usually covered with a velvety layer of feathers that acts as a “silencer”. Furthermore, the front end of the wings is equipped with fine bristles, similar to hairs, which “break” air turbulence (i.e. the formation of small eddies during flight), which is another source of noise. Finally, the tips of the feathers are soft and elastic, which reduces noise compared to wings with stiffer tips, and the friction between the feathers is also very low. The result? You can barely notice their flight.

Such discretion is an essential element for success in hunting. But another key piece of this puzzle is being able to discern the sounds made by prey in the dark.

In many species of the owl group, such as the different types of barn owls or barn owls, this feat is performed with the help of facial discs – the “sunken” regions around the animals’ eyes, which give them a distinctive look. curiously human, like someone wearing a decorated mask or large round glasses.

The facial discs are actually “parabolic antennas” that help the animal collect sound from the environment more efficiently. They are outlined by a ring of harder, intertwined feathers, which channel noises towards the owls’ ears, just like a person opening their hand in a cup around their own ear.

There are up to eight different types of feathers on these discs, all “designed” by natural selection to facilitate the channeling and conduction of sound in different ways. And some owls can even actively modify the structure of the disc, transitioning between “rest mode” and “attack mode”. As a result, certain species can even hear the footsteps of small rodents digging under a thick layer of snow.

Given all this, it is inevitable to look forward to future nighttime encounters with them with even more anxiety. And I smile even more when I see burrowing owls perched on a farm fence.

PS – The information above and a multitude of other fascinating data are in “What an Owl Knows”, a beautiful book by American science popularizer Jennifer Ackerman. Pardon the irresistible pun, I don’t know of a sharper pen than hers when the intention is to reveal the complexity of the planet’s birds.

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