43
as their air volumes expanded. This smooth change of surge frequency was achieved
while maintaining a constant stroke duration (0.4–0.5 s), presumably allowing
effi cient muscle contraction,” (Watanuki et al. 2003 ).
Bills, or Beaks
The Rostrum is the Latin term for a bird’s bill or beak. Bird’s rostrum consists of an
upper, chiefl y premaxillary and maxillary, and of a lower, or mandibular, half (Bock
and Kummer 1968 ). The bills of seabirds are typical examples of hierarchical and
complex multi-layered biological constructs with specifi c mechanical properties
(Soons et al. 2010 ) “consisting of a horny external layer with underlying bone and
a (epi-) dermal layer in between” (Soons et al. 2012a ). This keratinous covering is
to a certain extent molded along the shape of the supporting bones.
The soft cutaneous fragment of the skin is commonly restricted to a thin layer
between the periosteum and the stratum germinativum (also known as Malpighian
layer) of the epiderm. It is rich on many blood- vessels and nerves, the latter
occasionally penetrating the keratinous layer to terminate in tactile or sensory
corpuscles. The outer surface of the bill, the rhamphotheca (Lönnberg 1904 ), is a
continuously growing structure in most birds (Stettenheim 1972 ); so bill morphology is determined by rates of both growth and wear. The thickness of this keratinous
layer is on the order of 3 mm. Inter-individual changes in bill morphology have been
viewed as passive refl ections of changes in dietary protein content, changes in
abrasion, as an adaptive response to dietary shifts. Though strategic adjustment
of growth rates it was proposed (Bonser and Witter 1993 ) that changes in bill coloration
from different melanin contents may have a mechanical function. The deposition
of melanin can result in increased bill hardness, and this may have important implications for the maintenance of bill shape and, thus, foraging behavior.
Keratin is a robust biological material, which can protect the bone using absorption of energy from impacts (see Chap. 11 ). Thus, keratin on the bird beak possesses
unique properties as a shock absorber with regard to distribution of corresponding
forces and to prevention of bone microfracture (Frenkel and Gillespie 1976 ). If the
beak only contained of bone, or only contained of keratin, it would not be durable.
It is the interaction between the two different biological materials makes this organ
fi rm while remaining very light. These properties seems to be the driving force in
biomimetic key way with respect to design and development of self-repairing keratin-like protective sheaths (Soons et al. 2012a , b ).
Rhamphothecae sheaths show amazing diversity, and provide some of the most
compelling and easily appreciated examples of morphological adaptation in vertebrates
(Hieronymus and Witmer 2010 ). These include forceps for probing in sandpipers,
fi lters in ducks and fl amingos, “teeth” for gripping fi sh in mergansers and gannets,
and nutcrackers in hawfi nches. A widely distributed feature of rhamphothecae that
appears to be unrelated to their adaptive roles in feeding and display can be seen in
marine birds such as albatrosses, in which the skin of the rhamphotheca is separated
into several plates (Soldaat et al. 2009 ) (Fig. 1.9 ). This condition, referred to as a
“compound rhamphotheca” (Lönnberg 1904 ) contrasts with the continuous cornifi ed
1.2 Part I: Biomaterials of Vertebrate Origin. An Overview
as their air volumes expanded. This smooth change of surge frequency was achieved
while maintaining a constant stroke duration (0.4–0.5 s), presumably allowing
effi cient muscle contraction,” (Watanuki et al. 2003 ).
Bills, or Beaks
The Rostrum is the Latin term for a bird’s bill or beak. Bird’s rostrum consists of an
upper, chiefl y premaxillary and maxillary, and of a lower, or mandibular, half (Bock
and Kummer 1968 ). The bills of seabirds are typical examples of hierarchical and
complex multi-layered biological constructs with specifi c mechanical properties
(Soons et al. 2010 ) “consisting of a horny external layer with underlying bone and
a (epi-) dermal layer in between” (Soons et al. 2012a ). This keratinous covering is
to a certain extent molded along the shape of the supporting bones.
The soft cutaneous fragment of the skin is commonly restricted to a thin layer
between the periosteum and the stratum germinativum (also known as Malpighian
layer) of the epiderm. It is rich on many blood- vessels and nerves, the latter
occasionally penetrating the keratinous layer to terminate in tactile or sensory
corpuscles. The outer surface of the bill, the rhamphotheca (Lönnberg 1904 ), is a
continuously growing structure in most birds (Stettenheim 1972 ); so bill morphology is determined by rates of both growth and wear. The thickness of this keratinous
layer is on the order of 3 mm. Inter-individual changes in bill morphology have been
viewed as passive refl ections of changes in dietary protein content, changes in
abrasion, as an adaptive response to dietary shifts. Though strategic adjustment
of growth rates it was proposed (Bonser and Witter 1993 ) that changes in bill coloration
from different melanin contents may have a mechanical function. The deposition
of melanin can result in increased bill hardness, and this may have important implications for the maintenance of bill shape and, thus, foraging behavior.
Keratin is a robust biological material, which can protect the bone using absorption of energy from impacts (see Chap. 11 ). Thus, keratin on the bird beak possesses
unique properties as a shock absorber with regard to distribution of corresponding
forces and to prevention of bone microfracture (Frenkel and Gillespie 1976 ). If the
beak only contained of bone, or only contained of keratin, it would not be durable.
It is the interaction between the two different biological materials makes this organ
fi rm while remaining very light. These properties seems to be the driving force in
biomimetic key way with respect to design and development of self-repairing keratin-like protective sheaths (Soons et al. 2012a , b ).
Rhamphothecae sheaths show amazing diversity, and provide some of the most
compelling and easily appreciated examples of morphological adaptation in vertebrates
(Hieronymus and Witmer 2010 ). These include forceps for probing in sandpipers,
fi lters in ducks and fl amingos, “teeth” for gripping fi sh in mergansers and gannets,
and nutcrackers in hawfi nches. A widely distributed feature of rhamphothecae that
appears to be unrelated to their adaptive roles in feeding and display can be seen in
marine birds such as albatrosses, in which the skin of the rhamphotheca is separated
into several plates (Soldaat et al. 2009 ) (Fig. 1.9 ). This condition, referred to as a
“compound rhamphotheca” (Lönnberg 1904 ) contrasts with the continuous cornifi ed
1.2 Part I: Biomaterials of Vertebrate Origin. An Overview