Beak performs the functions of the “HAND” for the bird….. That’s right “the hand “not the mouth. The beak helps the birds to LOCATE, GRASP, TEAR, PICK, CARRY, PREEN etc. functions similar to the human hand. The birds predominantly use the beak to feed themselves hence the shape of the beak is adapted to their food type.
The beaks vary in shape across species but their basic structure remains same. There are two parts to a beak, the Upper part is upper mandible also called as MAXILLA and the lower mandible. These mandibles ( espl Upper) is internally strengthened by a complex layer of Bony spicules ( TRABECULAE) . these are seated in soft connective tissues that are surrounded by hard out layers of beak .
The upper mandible is supported by a three-pronged bone called the Intermaxillary. The upper prong of this bone is embedded into the forehead, while the two lower prongs attach to the sides of the skull. At the base of the upper mandible thin sheets of nasal bones are attached to the skull.
The lower mandible is supported by a bone known as the inferior maxillary bone—a compound bone composed of two distinct ossified pieces. The muscles that depress the lower mandible are usually weak, except in a few birds such as the starlings which have well-developed DIGASTRIC muscles that aid in foraging by prying or gaping actions. In most birds, these muscles are relatively small as compared to the jaw muscles of similarly sized mammals.
The beak is made of thin horny sheath of protein called Keratin . This is called RHAMPHOTHECA. This can be further subdivided as RHINOTHECA of upper mandible and GNATHOTHECA of lower mandible.
The RHAMPHOTHECA grows continuously in most birds, and in some species, the colour varies seasonally leading to colour changes in the beaks (Egrets during breeding)
In some birds a few parts of the RHAMPHOTHECA are shed each year after the breeding season, while some pelicans shed a part of the bill called a “BILL HORN” that develops in the breeding season
In most birds the RHAMPHOTHECA is a single Seamless entity but in some birds they are compound structures made up of several pieces
Each Mandible has cutting edges called TOMIA. In most birds, these range from rounded to slightly sharp, but some species have evolved structural modifications that allow them to handle their typical food sources better like
Seed eating birds have ridges in their TOMIA that helps them slice the seeds.
Falcons have a sharp projection in the MAXILLA called the “TOOTH”. This is used to sever their Prey’s body and rip them apart. Birds eating large insects and reptiles have one or more projections like Kites and Shrikes
Fish-eating species have Saw tooth serrations, which help them to keep hold of their slippery, wriggling prey
The Snail eaters or hard shelled prey eaters have Brush like projections that help create friction and hold hard prey
Serrations in Hummingbird’s TOMIA helps them function as Nectar eaters and hold and cut through the waxy floral parts
TOMIA is also used for identification of bird species.
It is the “highest middle lengthwise line of the bill” and runs from the point where the upper mandible emerges from the forehead’s feathers to its tip.
The shape or colour of the Culmen can also help with the identification of birds in the field.
The GONYS is the ventral ridge of the lower mandible .This spot triggers begging behaviour in the chicks. The chick pecks at the spot on its parent’s bill, which in turn stimulates the parent to regurgitate food.
It is the junction of the upper and lower mandibles
The GAPE is the interior of the open mouth of a bird, and the GAPE flange is the region where the two mandibles join together at the base of the beak. The width of the gape can be a factor in the choice of food. It is often used to identify the bird in connection with its length with respect to the eye.
Types of Beaks:
Laterally Flattened : The bill is pressed from sides , making it higher than its width . This is found in birds that need to see what they are holding . Ex: Aquatic Kingfisher, Hornbills
Dorso –Ventrally Flattened : The bill is pressed from Top to bottom , making it more wide than high . Ex : Dry land Kingfisher, Thicknee
Notched / Toothed : Large serrations at end of Mandible ( usually upper), this helps in holding and tearing the prey. Ex : Birds of Prey, Barbets
Casque : A hollow tube that runs for varying length of Maxilla . This is used for producing louder calls : Ex Hornbills
Serrated: Small sharp hooks along the cutting edge of the beak. Used for Gripping and cutting : Ex Hornbills.
Spatulate :It is Dorso-ventrally flattened , straight for its whole length with a rounded spoon shaped tip. This helps in catching Aquatic prey. Ex : Spoonbills
Kinked : The Laterally flattened beak has a marked sudden bend. This is useful for filter feeding just beneath the water surface . Ex : Flamingo
Decurved : The beak curves downwards toward its whole length. This helps the birds probe for prey hidden in soft soil. The beak tip has sensors that help the birds to detect prey. This also helps birds to see their prey better and catch them easily .Also birds feeding on Nectar can have better visibility to direct their beaks into the flower . Ex : Bee Eater, Curlew, Sunbird
Recurved :The beak curves upwards at the tip. This helps the bird to feed from the surface of water by moving its beak sideways . EX: Pied Avocet
Conical : These are broad with circular base tapering rapidly toward the tip . They are used to crush seeds and fruits. Shorter the bill higher the crushing force exerted. Ex: Seedeaters like Sparrows, Finches, Larks
Flat Conical : They are like conical beaks but are much longer and slender than the beaks of seedeaters.
Some may be
- Slightly curved/Hooked : Cuckoos
- Serrated : Coursers
- Notched/toothed : Rollers
These adaptations help in picking and holding prey from foliage
Short Conical : These are weak beaks, they are wider than they are high. They can open very wide and are used to catch prey that are in swarms.
The bird just opens its mouth as wide as possible and flies into the swarm at high speed. This is much more energy efficient than picking a target and going after it. Ex : Nightjar, Swallows
Hooked :These beaks have a sharp hook at the end of Maxilla. This hook has different uses Meat eaters : To tear into flesh of the prey, sever its vertebrae . Ex : Birds of Prey
Fruit eaters : To tear into hard outer shell of fruits . Ex :Parakeets
Aquatic Prey : Secure Slippery prey while diving, flying or swimming . Ex: Gulls, Cormorants
Tubular : They are simple beaks that are circular without serrations or hooks. The slender beak curves downwards in the end to a rounded tip. This helps the bird see the prey/food easily. They are suitable for pecking at small food items that are usually stationary. Ex : Doves, Lapwings
Spear- Shaped : They are Laterally flattened enabling the bird to see forward in Binocular vision clearly. The birds with this type of beak are all meat eaters. This bill is also used as a weapon to protect and attack, used to exhibit mating behaviour in Bill Clattering or bill grabbing. Ex : Indian Darter
Shovel Shaped: This is a Dorso-Ventral flattened designed .It resembles a slipper or shovel . This is useful in a feeding method called Dabbling, where the bird opens and closes its mouth in rapid movements. This helps in capturing small floating prey on surface of water. The sides of the bill are covered with small fine filters and in case of vegetarians some serrations. Ex.: Ducks, Geese
Chisel- Shaped : They are reinforced , triangular shaped beaks. They are very hard and used to dig /peck into wood or ground in search of prey or to make nest . Ex : Woodpeckers, Wrynecks
Crackers : They are laterally flattened beaks with the Maxilla and lower mandible having a gap. The mandibles are serrated and help grab the prey. The gap helps in holding the prey and exerting a force to break the shell like a Beatle nut cracker. Ex : Asian open bill
Skimmers : The Maxilla is shorter than the lower Mandible. This helps the bird skimthe water surface and the Maxilla is used to trap any prey that is skimmed using the lower Mandible : Ex Indian Skimmer
Text Source : Wikipedia, Beat About the bush -Birds by Trevor Carnaby
Pictures : Saravanan Janakarajan