West LA Times

Hummingbirds, known for their ability to hover near flowers with precision, have been the subject of extensive research concerning their flight mechanics. However, less is understood about how their sense of touch aids them in sipping nectar without colliding with flowers. While most studies on touch processing in the brain focus on mammals, bird brains differ significantly from mammal brains.

Recent research led by UCLA and published in Current Biology reveals that hummingbirds create a 3D map of their body through neuron activation in two specific forebrain regions. These neurons fire when gusts of air touch feathers on the leading edge of their wings and skin on their legs. Additionally, receptors on their bill, face, and head contribute to this sensory mapping. The intensity of air pressure—affected by proximity to objects—is detected by nerve cells at the base of feathers and leg skin and transmitted to the brain to gauge body orientation relative to an object.

The study also included zebra finches, which share a similar neural organization but exhibit slightly less sensitivity compared to hummingbirds. This suggests these neural areas are crucial for the specialized flight dynamics of hummingbirds. The findings enhance understanding of animal perception and navigation and could inform more humane treatment practices.

Humans have a tactile map in the brain that progresses from toes at the center down to legs, back, face, and hands—the latter areas being larger due to frequent use for touching tasks. "In mammals, we know that touch is processed across the outer surface of the forebrain in the cortex," said Duncan Leitch, corresponding author and professor at UCLA. "But birds have a brain without a layered cortex structure... We showed exactly where different kinds of touch activate specific neurons."

Previous studies using dye injections indicated that birds' brains process touch differently: one forebrain region for face/head touch and another for body touch. For example, owls have talon-specific touch centers instead of general face-touch regions.

Leitch's team observed real-time neuron firing by placing electrodes on hummingbirds and finches while gently touching them with cotton swabs or puffs of air. A computer amplified these signals into sound for easier analysis. Their experiments confirmed distinct mapping regions for head/body touch in birds' forebrains and demonstrated air pressure's role in activating neuron clusters.

Particularly large clusters reacted to wing-edge stimulation via puffs of air—a mechanism believed essential for nuanced flight adjustments. Additionally, feet were found highly sensitive with significant brain representation likely aiding perching behavior; this sensitivity may be even greater in parrots or other grasping birds.

Researchers identified receptive fields triggering neuron firing upon contact—especially small fields on hummingbird bills/face/head indicating high sensitivity necessary for precise flight maneuvers compared to larger fields in finches.

"Hummingbirds were often reacting to the slightest thresholds we could give them," Leitch noted.

Understanding diverse animals' tactile mapping could advance sensor technologies like prosthetic limbs or autonomous devices but improving animal welfare remains an immediate application.

"If we can understand how animals perceive their sense of touch," Leitch added, "we can develop practices that are less disturbing."