A hummingbird’s tongue is an incredible anatomical adaptation that allows it to efficiently feed on nectar. When at rest, a hummingbird’s tongue is curled up inside its bill. But when the bird sees a flower, it has the ability to quickly stick its tongue out to lap up nectar. So what makes a hummingbird’s tongue able to rapidly extend like this and adhere to surfaces? The answer lies in the unique anatomical structures and physiological processes that have evolved specifically for nectar-feeding.
Anatomy of a Hummingbird Tongue
The hummingbird tongue contains several specialized structures that allow it to dart out and stick to surfaces:
- Forked tip – The end of the tongue splits into two tubular tips which allows more surface area for nectar collection.
- Fringed edges – The outer edges have tapered, hair-like structures called lamellae which allows nectar to move into the grooves of the tongue.
- Grooves – There is a deep groove down the length of the tongue which allows nectar to move through capillary action.
In addition, the tongue contains an extraordinary number of muscle fibers. These allow the tongue to rapidly dart out of the bill and then retract.
Hyoid Apparatus
The tongue is attached to a unique bone called the hyoid apparatus. This consists of a loop of bones that surrounds the tongue muscles. When the hummingbird wants to stick out its tongue, the hyoid apparatus acts as a catapult, shooting the tongue forward at high speeds. It provides a firm platform for the tongue muscles to push against.
Extending the Tongue
Hummingbirds have two sets of muscles that allow their tongue to rapidly shoot out of their bill:
Intrinsic Tongue Muscles
The intrinsic tongue muscles run along the length of the tongue itself. When these contract, they shorten the tongue, quickly ejecting the fluid-filled tip out of the bill. Studies show that intrinsic muscle contraction happens in only 0.03 seconds! These muscles allow precision control of tongue projection.
Extrinsic Protractor Muscles
The extrinsic protractor muscles connect the tongue to the hyoid apparatus. When these muscles contract, they pull the hyoid apparatus forward, acting like a catapult for the tongue. High-speed X-ray videos show that these muscles shoot the hyoid forward at speeds of over 500 mm/s, propelling the tongue tip even faster.
Sticky Saliva
Hummingbirds produce a unique saliva that helps their tongue adhere to surfaces. This sticky saliva contains large amounts ofvifrfc polysaccharides. These long chain sugar molecules act as adhesive hydrogels.
When the tongue touches a surface, shear forces spread the saliva, helping the tongue stick. This allows hummingbirds to efficiently collect liquid nectar against gravity.
Interestingly, adding nectar to the saliva makes it even sticker. This is because nectar contains even more polysaccharides which reinforce the hydrogels. The more nectar a hummingbird drinks, the sticker its tongue gets!
Capillary Action
The tongue’s forked tip and fringed edges are perfectly designed to utilize capillary action to draw nectar in. Capillary action refers to the ability of a liquid to flow against gravity in narrow spaces.
The grooves on a hummingbird’s tongue create two types of capillaries:
Fringed Edges
The tapered lamellae along the tongue’s edges create narrow, hair-lined channels. These allow nectar to be drawn into the microscopic spaces through capillary action.
Central Groove
The central groove forms a larger capillary. Once nectar is drawn into the edge lamellae, it moves through the groove via capillary action. This allows the bird to collect a mouthful of nectar.
Wicking Saliva
Studies show that hummingbird saliva also utilizes capillary action to help draw nectar onto the tongue. The polysaccharides in the saliva essentially “wick” nectar through capillary rise.
This wicking saliva coats the tongue and fills the capillaries, which helps drive nectar through the microscopic channels through fluid dynamics. This allows hummingbirds to take advantage of multiple mechanisms to harness capillary forces.
Lapping and Pumping
Hummingbirds use two main techniques to collect nectar with their specialized tongues:
Lapping
During lapping, the hummingbird touches its forked tongue tip to a nectar pool. The tongue rapidly shoots out and retracts 5-15 times per second.
Each lick collects nectar through capillary action. By lapping repeatedly, the bird can efficiently gather up large amounts of nectar.
Pumping
Pumping involves inserting the tongue into the flower and rhythmically moving it in and out.
This action uses capillary forces and hydroadhesion to “pump” nectar onto the tongue. Pumping happens up to 30 times per second!
The tongue muscles are highly coordinated to pump at the ideal frequency for maximizing nectar intake rate.
Tongue Retraction
Hummingbirds retract their tongue via elastic recoil. When the intrinsic tongue muscles contract to project the tongue out, elastic tissues are stretched.
When contraction stops, these elastic tissues recoil like a rubber band, quickly snapping the tongue back into the bill. This lets hummingbirds retract their tongue within 0.01 seconds.
Combined with specialized tongue-hyoid muscles, this allows hummingbirds to extend and retract their tongue up to 20 times per second, enabling efficient nectar collection.
Behavioral Strategies
In addition to their unique anatomy, hummingbirds use several behavioral strategies to optimize nectar feeding:
- Seeking out curved flower shapes that allow tongue access.
- Approaching from below to reach nectaries.
- Targeting flowers with their bill tip to minimize tongue projection distance.
- Learning flower shapes and locations.
- Hovering in place to dip their tongue into multiple flowers.
These behaviors complement the hummingbird’s specialized tongue anatomy to further improve nectar feeding performance.
Evolutionary Adaptations
The hummingbird tongue is an incredible example of evolutionary adaptation:
| Anatomical Structure | Evolutionary Adaptation |
|---|---|
| Forked tongue tip | Increases surface area for nectar uptake |
| Fringed tongue edges | Allows capillary action to draw nectar onto tongue |
| Grooved tongue | Forms capillary channels to transport nectar |
| Hyoid catapult mechanism | Rapidly extends tongue at high speeds |
| Sticky saliva | Adheres tongue to surfaces to collect nectar |
These adaptations allow hummingbirds to tap into minute nectar supplies with incredible speed and efficiency. They have enabled hummingbirds to access food sources unavailable to other animals.
Energy Efficiency
Hummingbird feeding is extremely energy efficient. The tongue extensions require only minute muscle movements. Yet they provide an outsized energy gain from nectar.
This allowed hummingbirds to tap into a new ecological niche as specialized nectar feeders. Their remarkably effective tongue gives them access to a reliable food source that fueled their unique lifestyle.
Conclusion
The hummingbird tongue is one of the most specialized anatomical structures in the animal kingdom. The tiny birds have evolved extraordinarily effective mechanisms for nectar extraction.
Lightning fast tongue projection, capillary action, and hydroadhesion work together to allow hummingbirds to rapidly feed. Their ability to exploit flower nectar by optimally adapting their tongue anatomy and physiology has enabled hummingbirds to thrive by filling a unique ecological role.
