New research reveals hummingbirds’ remarkable sense of touch

By Stephen Beech via SWNS

Hummingbirds' "acute" sense of touch helps them to hover near a flower to feed - without bumping into it, reveals new research.

The tiny birds create a 3D body map when neurons in the brain "fire" as gusts of air touch their wings, according to the findings.

Scientists say their findings add to knowledge of how animals perceive and navigate in their worlds - and can help identify ways to treat them more humanely

While hummingbirds’ flight mechanics have been previously studied in detail, far less is known about how their sense of touch helps them sip nectar from a flower without bumping into it.

Most of what scientists know about how touch is processed in the brain comes from studies on mammals, but bird brains are very different from mammal brains.

The new study, published in the journal Current Biology, shows that hummingbirds create a 3D map of their body when neurons in two specific spots of the forebrain fire - as gusts of air touch feathers on the leading edge of their wings and skin of their legs.

The research team explained that receptors on the birds' bill, face and head also work toward that end.

They discovered that the air pressure’s intensity, influenced by factors such as proximity to an object, is picked up by nerve cells at the base of the feathers and in the leg skin and transmitted to the brain, which gauges the body’s orientation relative to an object.

Zebra finches, also studied by the research team, have the same general organization with slightly less sensitivity in some areas than hummingbirds, suggesting that those areas help with highly specialized hummingbird flight dynamics.

The researchers explained that humans produce a tactile map of the body that progresses from the toes at the center of the brain, down to the legs, back and a much larger area that represents touch to the face and hands.

Those areas, used for touching and touch tasks, are enlarged in the human brain.

Study corresponding author Professor Duncan Leitch said: “In mammals, we know that touch is processed across the outer surface of the forebrain in the cortex.

“But birds have a brain without a layered cortex structure, so it was a wide-open question how touch is represented in their brains.

"We showed exactly where different kinds of touch activate specific neurons in these regions and how touch is organized in their forebrains.”

Previous research in which birds were injected with dye showed their brains have one region in the forebrain to process touch to the face and head, and a different one for touch anywhere else on the body.

In owls, for example, touch centers that typically correspond to face touch are devoted solely to talons.

Leitch, of the University of California, Los Angeles (UCLA), along with colleagues at the Royal Veterinary College and the University of British Columbia were able to observe neurons firing in real time by placing electrodes on hummingbirds and finches and touching them gently with cotton swabs or puffs of air.

A computer then amplified the signals from the electrodes and converted them to sound for easier analysis.

The experiments confirmed that touch for the head and body is mapped in different regions of the forebrain.

They also showed for the first time that air pressure activates specific clusters of neurons in those regions.

Examination of the wings showed a network of nerve cells that likely sent a signal to the brain when activated by puffs of air on the feathers.

The research team found "particularly large" clusters of brain cells that reacted to stimulation of the edges of wings, which they think help the birds adjust flight in a nuanced way.

The researchers also discovered that the feet are acutely sensitive to touch and that touch had a large representation in the brain, presumably to help with perching.

The team believes these areas may be even larger in parrots and other birds that use their feet to grasp and move objects.

They said that in hummingbirds some of these fields - especially on the bill, face and head - were very small, meaning they could sense the lightest touch.

Zebra finches had the same but larger receptive fields, suggesting these regions in finches are not quite as sensitive and probably of greater relevance to hummingbirds that rely on constant, steady precision flight.

Leitch said: “Hummingbirds were often reacting to the slightest thresholds we could give them."

He added: “If we can understand how animals perceive their sense of touch, we can develop practices that are less disturbing to them."