Some hawks evolved super hearing abilities to locate prey

Owls are famous for their ability to hear exactly where their prey is hiding, even in complete darkness. But a surprising new study shows that owls aren’t the only raptors with this impressive skill. Harriers, a type of hawk found around the world, also have specialized hearing abilities that help them locate prey by sound.

An international team led by researchers from the University of Lethbridge in Canada and Flinders University in Australia has uncovered unexpected owl-like traits in the ears and brains of several harrier species.

The findings reveal that harriers have independently evolved several adaptations that allow them to hunt more effectively by sound.

Hunting prey by sound and sight

“Until recently, it was assumed that all their hearing adaptations were unique to owls. However, our study shows that harriers have independently evolved several key adaptations for finding prey by sound,” said Sara Citron, a PhD student at the University of Lethbridge, who led the study.

Scientists have long praised owls for their fine-tuned hearing, which allows them to zero in on small prey like mice in total darkness.

Harriers, on the other hand, primarily hunted by sight – much like most hawks were believed to do. But the new research reveals that harriers are much more attuned to sound than previously believed.

Hawks with exceptional hearing

The research team focused on harriers because of their distinctive hunting style. Andrew Iwaniuk, senior author of the study, is an associate professor at Canada’s Center for Behavioral Neuroscience.

“Hawks tend to hunt primarily by sight. But unlike other hawks, harriers fly low over tall grass with their beak pointed to the ground,” said Iwaniuk. “During this so-called ‘quartering flight,’ they are not only looking for prey, they are also listening for it.”

“The Australian Spotted Harrier is a great example. When you look at this species’ face, you can see a distinctive disc-shaped face, which may improve their prey localization just like owls,” added co-author Aubrey Keirnan, a PhD student at Flinders University.

Older behavioral studies had already shown that harriers can locate sounds with surprising accuracy, much like owls. But the anatomical reasons behind this ability had remained a mystery.

Brains tuned for prey

To investigate further, the researchers examined skulls and brains of harriers. They compared them to other hawks, using specimens from wildlife rehabilitators and museums in Canada and Australia. Researchers also looked at close relatives, such as the wedge-tailed eagle.

They found harriers, like owls, have large ear openings and two brain areas vital for pinpointing sound location.

“These auditory nuclei are found in the brainstem and compare the time at which sounds arrive at the left or right ear,” said co-author Vera Weisbecker, an associate professor at Flinders University.

“If a sound arrives at both ears at the same time, then the sound is coming from directly in front of an animal. If there is a delay, this indicates that the prey is more to the left or right.”

The hawks have enhanced hearing thanks to expanded brain regions, giving them an edge in detecting hidden prey.

Separate species, same solution

“Harriers have therefore evolved an auditory system similar to owls, enabling them to target sounds as accurately as owls in a remarkable example of convergent evolution of both brain and behavior in animals separated by over 60 million years,” Citron said.

However, the researchers are careful to note that these hawks are not quite on par with owls when it comes to hearing.

“There are several other features that help owls with their keen hearing which we did not find in harriers,” Citron explained.

“For example, some owl species have asymmetric ears that allow them to locate sound with greater acuity, and these owls also have several other enlarged brain regions that were not enlarged in harriers.”

This explains why owls can hunt in complete darkness, while harriers remain daytime hunters.

Conservation strategies for harriers

The researchers believe their findings could help guide future studies on bird anatomy and behavior, especially when it comes to conservation.

“Anatomical studies like ours are a window into how a bird perceives the world around it, which can be extremely useful for bird conservation,” Iwaniuk said.

“For example, harriers’ reliance on sound for prey location means that they are likely more sensitive to traffic and industrial noise. This could be contributing to the large decreases in Northern Harrier populations we have seen in Canada.”

By better understanding how these birds detect prey, scientists can learn more about the challenges they face in modern environments. This knowledge could help design conservation strategies that account for noise pollution and other threats that interfere with their finely tuned senses.

The study adds to a growing body of research showing how diverse species can evolve similar traits when facing similar challenges – highlighting nature’s remarkable ability to find common solutions across vast evolutionary distances.

The study is published in the Journal of Anatomy.

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