Module 1.4- Beaks and Bills Flashcards
Describe the basic structure of beaks (& bills) Explain the impact that diet has had on the evolution of various beak structures
What is the main factor that influences the evolution of beak shapes?
Diet.
What factor other than diet influence the evolution of beak shapes?
Foraging habits
A bird specialised in eating seeds would be expected to have what kind of beak?
A thick beak designed for crushing
A wood pecking bird would be expected to have what kind of beak?
heavy, blunt beak designed to chisel
A shorebird would be expected to have what kind of beak?
long, delicate beak designed for probing
A raptor would be expected to have what kind of beak?
Sharp-edged, hooked beak designed for tearing skin, muscle and fur.
Which bones make up the underlying structure of a beak?
premaxillary and mandibular
How are the premaxillary and mandibular bones modified to form the beak?
local thickenings of the epidermis, made up of tightly packed keratinocytes that migrate outwards as they mature, cornifying as they progress outward.
How do the keratinocyte cells that make up the beak epidermis change as they migrate outwards?
They transition from an actively growing germinative layer to a fully cornified layer
Which direction do the keratinocytes in a birds beak migrate? What does this mean?
They migrate outwards, similar to that of human fingernails, meaning the beak of a bird is continuously growing.
What comprises the outer layer of the beak?
A Laminae of cornified cells called corneocytes, which form a hard, horn like sheath.
What is the name of the outer layer of the beak?
Rhamphotheca
What is the type of the cell that comprises the outer layer of the beak?
corneocytes
What is the type of cell that comprises the inner layers of the beak?
Keratinocytes
how is the outer layer of the beak (Rhamphotheca) maintained?
It is continuously replaced via growth and maturation of the epidermis as it is worn down by use.
What is the function of the outer layer of the beak (Rhamphotheca)?
provides a strong, durable structure for feeding, preening, breeding and defense
What are the two types of sensory receptors that can be found within the beak?
Magnetoreceptors and mechanoreceptors
What three functions other than feeding can the beak be used for?
May be used to perceive sensory information such as vibrations, temperature and pressure to assist with foraging and understanding the environment.
May function in orientation and migration with the use of magnetoreceptors located in the beak.
May assist with thermoregulation (Toco Toucans show vascular mechanisms for controlled heat exchange in the beak)
What is the name of the structure at the tip of the premaxilla in a beak?
Rhinotheca
What is the name of the structure at the tip of the mandible in a beak?
Gnatotheca
Where is the external nasal opening usually located on a birds beak?
On the basal end of the premaxilla (close to the face on the top part of the beak)
What one bird has external nasal openings located somewhere other than the normal position? Where are they located and why?
The New Zealand Kiwi has external nasal openings located on the cranial side of the Rhinotheca (tip of the beak) rather than the Premaxilla (close to the face). This is because they use it to detect prey in foraging.
Name the layers of the ventral (bottom) beak, from deepest (innermost) to most superficial (outermost)
Mandible (bone), Dermis, Epidermis (stratum germinativum, stratum corneum)
Name the layers of the dorsal (top) beak, from deepest (innermost) to most superficial (outermost)
Premaxilla (bone) and nasal cartilage, Dermis, Epidermis (stratum germinativum, stratum corneum), nasal passages
Why is the Toucan (Ramphastos toco) beak special?
It makes up a third of the birds length but less than 5% of it’s weight because it is comprise of a specialised sandwich like layering and an outermost layer of keratin hexagonal scales, giving it lightweight but strong formation.
What specialisation does the Monotreme bill contain to assist with locating prey?
They can detect electrical fields generated by the muscle contractions of their prey.
Describe the overall structure of the Platypus bill
Soft, rubbery, well supplied with nerves, covered with thin, extremely sensitive skin.
Roughly how many push-rod Mechanoreceptors are found in a Platypus bill?
46500
Roughly how many mucous gland Electroreceptors are found in a Platypus bill?
40000
Roughly how many sensory serous glands are found in a Platypus bill?
13500
Where are the mucous gland electroreceptors of the Platypus bill located?
In rostrocaudal (“from the nose to the tail”) rows in the skin of the bill.
Where are the push-rod mechanoreceptors of the Platypus bill located?
Distributed uniformly across the bill.
How do the sensory serous glands help the Platypus find prey?
They assist with the detection of electrical signals at close quarters, when the mechanoreceptors are also being used. This allows the Platypus to distinguish between prey and riverbed substrates.
