New studies indicate that harriers have evolved specific auditory adaptations in parallel with owls. This adaptation allows them to effectively stalk prey in thick cover. A team of Canadian and Australian researchers are at the helm of this study. There’s a lot of interesting anatomy and neurology that allows these birds to find prey concealed beneath thick grass. Research findings highlight the unique hunting foraging strategies of harriers as well as their population decline, especially in Canada.
Harriers range over much of North America, Australia, New Zealand, and Eurasia, including Europe, the Middle East, and most of Central Asia. More recently, they have been observed employing unconventional methods to find prey. Harriers have one specific advantage over hawks. Where hawks depend primarily on their wonderful eyesight, harriers use their excellent hearing to find ground-dwelling prey. The Australian Spotted Harrier is a fantastic illustration of this adaptation. Such a disk-shaped facial disk structure aids it in determining the source of sounds much better.
Unique Anatomical Features
Focusing on harriers as an illustrative example, the study identifies a number of important anatomical characteristics that set them apart from their raptor counterparts. Interestingly, harriers develop both enlarged ear openings to help with sound collection and two expanded brain areas important for sound localization. These adaptations make it possible for them to accurately determine the direction of sounds. This skill becomes incredibly handy when they’re foraging in more difficult habitats such as dense tall grass.
“These auditory nuclei are found in the brainstem and compare the time at which sounds arrive at the left or right ear,” – Associate Professor Vera Weisbecker
This mechanism underlies how harriers are able to locate their prey based upon sound alone. If a sound reaches both ears at the same time, that’s a clue that the source must be directly in front. An opposed delay in arrival time of sound means the prey is to the side.
For this research, the scientists did a long and detailed study of harrier anatomy. For this study, they drew from the collections of wildlife rehabilitators and museums in Australia and Canada. They paired harriers with similar, evolutionarily related hawk species such as the wedge-tailed eagle. This type of comparison allowed them to pinpoint specific evolutionary adaptations that improve sound detection.
Hunting Techniques
Harriers show a distinctive flight style known as “quartering.” They fly extremely low over grassy terrains, with their mouths open and angled downwards. This behavior is in notably sharp contrast to other hawks that hunt primarily via sight.
“Hawks tend to hunt primarily by sight. But unlike other hawks, harriers fly low over tall grass with their beak pointed to the ground,” – Dr. Andrew Iwaniuk
While on this quartering flight, harriers are highly attuned to producing sounds from possible prey. Combined, these sensory advantages improve their hunting success in dark or murky habitats.
“During this so-called ‘quartering flight,’ they are not only looking for prey, they are also listening for it,” – Dr. Andrew Iwaniuk
These adaptations offer significant advantages as they allow harriers to thrive in diverse habitats while facing challenges posed by habitat loss and population declines.
Implications for Conservation
The research team’s findings are an important step in understanding the evolutionary biology of harriers. More importantly, they hold greater implications for bird conservation initiatives. Their research, published in Proceedings of the Royal Society B, tracks how adaptations to listening have helped them both evade predators and find prey under the sand.
“Anatomical studies like ours are a window into how a bird perceives the world around it, which can be extremely useful for bird conservation,” – Dr. Iwaniuk
Our findings will contribute to understanding the causes of the alarming population declines seen in Northern Harriers throughout Canada. Knowing how these birds use sound to hunt will give us huge clues. Understanding how they move will inform better conservation policies to protect them and their habitats and ensure their continued existence.
“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,” – Sara Citron
Perhaps most importantly, the research calls for more studies on harriers. It’s important to know their specific life history traits and what makes them fit in their local ecosystems.