Both birds and humans use their tongues for tasting, swallowing, and vocalizing. However, a bird’s tongue has evolved for different purposes than a human’s tongue, resulting in some key anatomical differences.
Bird Tongue Functions
A bird uses its tongue primarily for:
- Capturing food – A bird’s tongue has backwards facing barbs called papillae that help it grasp and manipulate food.
- Swallowing – Their tongues have bristles that help push food back into the throat.
- Drinking – Capillary action draws water up the grooves of a curled tongue.
- Thermoregulation – Flicking their tongues in and out releases excess heat.
- Cleaning – Birds use their tongues to keep their beaks and feathers clean.
- Singing – The tongues of songbirds are important in forming notes and calls.
Human Tongue Functions
In comparison, the human tongue is adapted for:
- Speech – With a broader range of motion, our tongues can form words.
- Taste – Our tongues have many taste buds for detecting sweet, sour, salty, bitter, and umami flavors.
- Chewing and swallowing – Along with our teeth, our tongues help mash up food.
- Oral hygiene – Our tongues help clean food debris from our teeth.
Tongue Structure
Structurally, bird and human tongues have some key differences:
Feature | Bird Tongue | Human Tongue |
---|---|---|
Size relative to body | Small | Large |
Shape | Long and thin | Short and wide |
Papillae | Hard, stiff, and pointed backwards | Soft and rounded |
Taste buds | Very few concentrated at the back | Thousands all over the surface |
Muscles | Minimal | Extensive |
As you can see, bird tongues are optimized for grasping food, while human tongues are better adapted for intricate movements and tasting.
Tongue Bones
One major difference is that birds have a tongue bone called a hyoid. The hyoid stretches from the back of the tongue to the top of the larynx. It anchors the tongue in place but allows it to protrude slightly.
Humans lack a tongue bone. Our tongues are entirely muscular. The absence of a rigid hyoid gives our tongues great mobility for speech.
Saliva
Birds do not produce much saliva. Their tongues are fairly dry. What little saliva they have is used to help swallow food.
Humans make about 1-1.5 liters of saliva per day. Our wet, mucus-rich saliva lubricates food and contains enzymes to begin chemical digestion.
Taste
Compared to humans, birds have a very limited sense of taste. They lack taste receptor diversity, having only between 24-40 working taste buds.
In humans, the average tongue is covered with 2,000-10,000 taste buds. We have receptors dedicated to five primary tastes: sweet, sour, salty, bitter, and umami.
Birds can only detect salt, sour, and bitter – flavors that signal spoilage or toxicity. They lack receptors for sweet or umami tastes.
Sensory Differences
Birds rely far more on vision and less on taste while foraging. Their excellent color vision helps them locate ripe fruits and seeds.
Humans cannot see well in low light conditions. We depend more on our sophisticated sense of taste and ability to detect a wide range of flavors.
Swallowing
A key role of the tongue is propelling food and liquid into the esophagus. Birds and humans swallow differently:
- Birds use their tongues to catch and manipulate food at the tips of their beaks. Backward spines on the tongue grip food and push it into the throat.
- Humans use our tongues to position food between the teeth for chewing. The tongue forms food into a bolus that is squeezed down the throat by muscles.
Because of these different techniques, birds are able to swallow larger prey items relative to their body size.
Drinking
Birds cannot sip or suck up water like we can. However, they have adapted a special mechanism for drinking:
- The bird curls its tongue backwards into a tube, exposing grooves on the top surface.
- Pressing the lower mandible into water, capillary action draws liquid up the grooves.
- Once the tongue is charged with water, the bird retracts it and closes its beak, trapping the water inside.
- Craning its neck, the bird allows gravity to pull the water down its throat.
This allows birds to drink continuously without needing to stop and swallow. Some birds can absorb water at rates over 10 ml/sec – more than an order of magnitude faster than humans.
Cleanup
Grooming is another essential function of bird and human tongues:
- Birds use their tongues to wipe and clean debris from their beaks. Their slightly abrasive papillae help scour the keratin beak.
- Humans employ our tongues to clear food from our teeth and mouth. The tongue’s mobility and moisture are well suited to cleaning the hard surfaces of teeth.
For birds, a clean beak is critical to eating and preening. For humans, cleaning the teeth prevents cavities and disease.
Thermoregulation
Birds use their tongues to release excess heat through a process called gular fluttering:
- A overheated bird will relax its jaw and rapidly flick its tongue in and out, often while panting.
- As saliva evaporates from the tongue’s surface, it carries away heat.
- Rapid gular fluttering can cool a bird by 2-3°C within a few minutes.
Humans cool ourselves using a different mechanism – sweating. We have over 3 million sweat glands distributed across our skin. Evaporation of sweat dissipates heat and allows us to maintain a stable body temperature.
Singing
While all birds use their tongues to vocalize, songbirds have evolved specially adapted tongues:
- Songbirds have a large syrinx vocal organ instead of vocal cords.
- Their tongues function as a movable whistle, changing shape to modulate syrinx output.
- Special fibers in the tongue control fine adjustments that determine pitch and timbre.
- Combined with their syrinx, songbirds produce extremely complex calls.
In humans, vocal cords located in the larynx are the main source of sound production. The position of our tongue mainly affects speech articulation and vowel sounds.
Injuries
Damage to the tongue impairs function in both birds and humans:
- Tongue injuries in birds are most often caused by collisions with objects such as windows or fences.
- Common tongue injuries in humans include bites, piercings, burns, and infections.
- A bird with a swollen or damaged tongue may have difficulty eating, drinking, and regulating heat.
- A human with tongue impairment can suffer problems with speech, taste, swallowing, and breathing.
Fortunately, minor injuries usually heal within a few days in both species. More extensive wounds may require veterinary or medical intervention.
Diseases
Birds and humans are prone to some similar tongue diseases and conditions:
Condition | Birds | Humans |
---|---|---|
Oral thrush | Yes | Yes |
Glossitis (inflammation) | Yes | Yes |
Glossodynia (pain) | Rare | Yes |
Oral cancer | Rare | Yes |
Glossoptosis (displaced tongue) | Yes | Rare |
Oral thrush from Candida yeast overgrowth is common to both groups. Birds appear less prone to tongue cancer than heavy tobacco and alcohol users.
Evolution
Despite their differences, bird and human tongues share anatomical elements and embryological origins as vertebrates. The tongues of both evolved from the same pharyngeal arches:
- The back 2/3 of the bird’s tongue develops from the first pharyngeal arch.
- The front 1/3 develops from the second and third arches.
- The human tongue originates from all three pharyngeal arches.
While adapted to different functions, the muscle, connective tissue, nerve, and salivary components of bird and human tongues are still homologous structures, pointing to our shared ancestry.
Conclusion
To recap, while bird and human tongues share some general design elements, they have distinct specializations:
- Birds prioritize food manipulation, temperature control, and vocalization.
- Humans emphasize speech articulation and taste sensation.
Evolution shaped bird tongues for capturing prey and regulating heat, while human tongues became adapted for complex language and detecting a multitude of flavors.
However, both play integral roles in key functions like swallowing, drinking, and hygiene. The tongue’s importance for birds and humans highlights how evolution conservatively modifies fundamental structures to fill diverse ecological niches.