Have mask, can fly (Image: Michael Gore/FLPA)

Species: Lanius nubicus

Habitat: Open forest glades of Eastern Europe and the Middle East, flying into the sun

The masked shrike has a dark stripe across its eyes, a little like the mask worn by fictional hero Zorro. His distinctive face-wear allowed him to defeat villains with his trusty rapier without revealing his true identity – but why did the masked shrike evolve its version?

One idea is that it is also a disguise. The black markings might allow a bird to focus on prey while appearing to look elsewhere. In theory, preyed-upon creatures might be less likely to flee if they do not realise a predator is staring at them.


Or perhaps the mask increases the shrike’s likelihood of grabbing a meal when it swoops in for the kill. The stripe might help the birds guide their beak when targeting prey, which would be handy given that they use a “perch and pounce” hunting style. Masked shrikes tend to sit and wait for beetles, grasshoppers or even small lizards to come close enough before they attack.

Then again, maybe the mask is there to fool the shrike’s predators rather than its prey. It makes the bird’s eyes look larger – and might make it seem more intimidating.

To find out which – if any – of these ideas is correct, Reuven Yosef from Ben-Gurion University in Israel took a drastic approach: he unmasked the shrike.

With Polish colleagues, Yosef caught seven birds and used gouache paint to turn their stripes white – the colour of the surrounding face – before freeing them, to investigate how they would cope without their masks. They also used black paint on the stripes of five other masked shrikes, to check that the paint itself wasn’t having any effect on behaviour. The researchers left a third group of shrikes paint-free.

The birds with black-painted masks hunted as well as the paint-free birds – but those painted white were significantly less successful. In particular, the unmasked shrikes did more of their hunting facing away from the sun, while black-painted and normal birds hunted into the sun.

So it seems that the masks act to reduce glare, allowing shrikes to see prey objects without being dazzled. That makes sense, says Graham Martin, an ornithologist at the University of Birmingham in the UK. Although you might normally turn your back to the sun in order to see something clearly, this means you end up throwing your giveaway shadow in front of you – something the shrike wants to avoid. “By foraging going into the sun, the birds become more or less invisible,” says Martin.

One mask potentially explained, then – but eye-masks are also seen in tree frogs, dormice, racoons and killer whales, to name but a few. To work out the function of these masks, we’re going to need a lot more paint.

Journal reference: Behavioural Ecology, DOI: 10.1093/beheco/ars/005

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