What are bristles?
Most birds have whiskers which scientists refer to as bristles. They differ in the position they are found, their length and their fluffiness. Not surprisingly, they are a type of feather that is made up of a thin stiff hairlike structure which can have branching furry projections or none. They can be positioned in different areas of the bird’s head from the forehead in kiwi and around the top and side of the beak and even under the beak. Oilbirds have some of the longest bristles of around 39mm in length!
What is their function?
Facial bristles in birds have many different functions depending on the species. Unfortunately we can’t ask birds how they use their facial bristles or step out of our own perceptions into experiencing life through a bird’s eyes. However, we can design experiments that can provide us insights into the ways birds live their lives.The more we notice about the way birds sense their environment, the closer we are to understanding how they experience their worlds.
We can study the function of traits in different ways. We can look at the structure of the trait such as placing the bristles under a microscope. This is what some researchers did with specimens from natural history archives. They wanted to know if the bristles are similar to mammalian whiskers which are used to navigate the world through touch. To sense touch mammalian whiskers have a mechano-receptor at their base.
For example, when a cat’s whisker touches the wall its movement, physical energy, is picked up by the receptors at the base of the whisker and translated into electrical energy to tell the brain that there was a change in pressure from the environment. As it turns out from the microscope images, birds also have mechanoreceptors called Herbst corpuscles. It appears that both nocturnal birds such as kiwi and owls and diurnal birds, those active in the daytime, such as fantails have mechanoreceptors at the base of their bristles. This suggests that the bristles may function to help them sense their surroundings through touch.
To gain a deeper understanding about the function of traits we need to employ some detective work and observe the behaviour of animals to learn how they use those traits in their social and physical environment. Facial bristles are very prominent on nocturnal birds such as kiwi, Kakapo parrot and nightjars, which might make sense if they are used to help them feel their environment in the dark.
Whiskered auklets, a nocturnal seabird that breeds colonially in crevices in piles of rocks, have elaborate long feathers on their heads. These feathers may have multiple functions such as choosing mates and signaling their dominance. A group of researchers came up with an elegant way (or not so elegant if you ask the birds) to see if the bristles also gave the birds an advantage when navigating an unknown tunnel maze in the dark. They separated the 99 birds into those that had their bristles taped down and those that did not.
They then released them into the tunnel maze and observed how many times the poor birds bumped into the walls as they went through the tunnel maze. They found that those that had their bristles taped down bumped their heads twice as much as those that did not. These findings suggest that their bristles help them navigate the dark crevices that they breed in. We hope the birds had a swift recovery and didn’t suffer from severe concussions.
But what about the birds that visit my BirdBuddy? They are not a tunnel living nocturnal bird? Are the bristles just decorative? Do they have the same function or a different function? Very little is known about the function of the bristles across different bird species and it is safe to say, it is all up in the air. However, there are a few theories based on some evidence. Bristles between the eyes and beak may protect the bird’s eyes from particles when soaring through the air and catching flying prey.
The Iberian grey shrike feeds on large insects such as bumblebees, locusts and beetles as well as small reptiles and mammals such as lizards and mice, where it will use branches to impale them. They possess bristles between their eyes and beak which may act like a curtain to protect their eyes from prey and noxious chemicals emitted by some invertebrates.
However, to reach this conclusion scientists only examined the structure of the bristles and not how they function through observing the shrike’s behaviour. Nerve endings have also been found in the bristles of birds active in the daylight which suggests they may also feel their way around in their nest cavities, when finding the beak of their young begging for food or avoiding collisions when navigating through the air.
Next time a feathered friend pays a visit to your BirdBuddy, take a minute to notice their bristly faces and where their bristles are located. You may be surprised at how many species possess them.