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
