Extant Sauropsida
birds (finally)
lilac breasted roller,
Coracias caudatus
Photo: AMMurray
Learning objective 2: to be able to
recognize and describe different types of
feathers, and understand how contour
feathers and other anatomical adaptations
affect bird flight.
Amniota
Tetrapoda (land vertebrates)
Sarcopterygii
(lobe-finned “fish”)
Osteichthyes
(bony “fish”)
Gnathostomata
(jawed vertebrates)
Vertebrata
Mammalia
Reptilia
Lissamphibia
(modern amphibians)
Dipnoi
(lungfish)
Actinistia
(coelacanths)
Actinopterygii
(ray-finned fish)
Chondrichthyes
(cartilaginous fish)
Cyclostomata
(jawless fish)
Reptile Phylogeny
Archosauria
Aves
(birds)
Crocodylia
Reptilia
Testudinata
(turtles)
Sphenodon
(tuatara)
Lepidosauria
NB: The avian crown group is
sometimes called Neornithes, but we’ll
use Aves in ZOOL 224 (as in text book).
Squamata
(lizards)
Aves
• birds and their extinct relatives
• extant are immediately recognizable BUT:
– most ‘bird’ features evolved prior to bird lineage
• feathers, furcula, pneumatic bones, unique wrist
joint, uncinated processes
photos: AMMurray
feathers and flight
• evolved in non-avian dinosaurs
• inherited by their descendants (birds)
• (videos on bird origins and origin of flight)
Acheroraptor
Emily Willoughby, Own work, CC BY 3.0,
https://commons.wikimedia.org/w/index.php?curid=30194091
Artist's concept of Caihong, a crow-sized
iridescent dinosaur from the Jurassic
Period.
smithsonianmag.com; Velizar Simeonovski/The Field Museum
origin of feathers
• (from the video with Dr. Julia Clark)
– evolved first in non-avian dinosaurs
– after feathers evolved, were ‘co-opted’ for
flight = exaptation
• why did they evolve?
– insulation
– gliding
– thermoregulation (insulation and shading)
anatomy of a feather
• develop from feather
follicles = infoldings of
surface layer of skin
• each has its own blood
supply, muscles and
nerves
• predominantly formed of
keratin
• calamus anchors
feather to body within
the sheath
follicle
calamus
veterinkey.com/feather-follicle-extirpation
anatomy of a feather
• rachis = central axis
• from largest to smallest
branching: rachis, barb,
barbules
• barbs branch off from
the rachis, and the
barbules are what hold
the barbs of the feather
together to provide a
smooth outline
https://academy.allaboutbirds.org/feathers-article/
pterylae
• feathers are laid out on the body in distinct
tracts = pterylae
– some birds lack pterylae and feathers are
uniformly distributed over body
www.zoo.ufl.edu/courses/vertzoo/Images/Birdlab/FeatherTrack.jpg
Nestling Common Grackle showing pterylae
photo: Caleb G. Putnam
types of feathers
classified based on
morphology:
• plumulaceous
– no vane,
rudimentary rachis,
elongate barbules
on tuft of barbs
• pennaceous
– centra rachis with
hooked barbs to
form vane with
smooth edge
Prum and Brush 2003
types of feathers
• classify based on function (5 types)
– contour
– down
– semiplumes
– filoplumes
– bristles
Wing and tail feathers are pennaceous, and down
feathers are plumulaceous. Contour and semiplume
feathers are plumulaceous at their bases, and
pennaceous at their tips. The filoplume has barbs at
its tip, and the bristle has barbs at its base
https://academy.allaboutbirds.org/feathers-article
feather functions
• contour: cover surface of bird in
overlapping layers
– on the body = coverts or deck feathers
– specifically for flight = flight feathers
– on the wing = remex (pl. remiges)
https://www.fws.gov/lab/feat
heratlas/idtool.php
• asymmetrical to prevent twisting
• remiges on outer tip of wing = primaries; provide thrust
• remiges on trailing edge of wing = secondairies; form airfoil
– on the tail = retrix (pl. retrices)
• generally arranged in a fan shape; steering
• normally 6 pairs, more asymmetrical towards outer edges of
tail
feather functions
• down: thermal insulation
– small feathers with short rachis
– lie closest to skin
– no barbules, entirely plumulaceous in form
By Wouter Hagens - Own work, CC BY-SA 4.0,
https://commons.wikimedia.org/w/index.php?cur
id=103988002
feather functions
• semiplume: thermoregulation and streamlining
–
–
–
–
between down and contour in morphology
lie underneath contour feathers
long rachis but no vane
no barbules (entirely plumulaceous)
study.com
feather functions
• filoplume: sensory
–
–
–
–
short, simple with a few barbs at the tip
base is associated with nervous system
underlie contour feathers, mostly on the wings
nerves sense movement of filoplume and provide
information to brain about position and movement of
overlying contour feathers
http://people.eku.edu/ritchisong/feathers.html
feather functions
• bristle: sensory (tactile) and protection
– simplest feathers – central rachis with no or few barbs
at base
– concentrated at the base of the beak and around eyes
Eastern Whip-poor-will at Magee Marsh Wildlife Area, Ohio, May 3, 2015, by Joan Tisdale;
https://www.birdwatchingdaily.com/news/science/bird-basics-six-different-feather-types-explained/
feather colour
• from pigments
Plum-headed Parakeet ebird.org
– melanins in skin cells – blacks, greys, browns
– carotenoids from diet – reds, oranges, yellows
– porphyrins containing metals – e.g., iron red
• from structure
– scattering of light by cells of barbs – blues,
greens, purples
• mix of two
– e.g., parakeet green from yellow carotenoid
mixed with structural blue
bird aerial locomotion
•
•
•
•
very complex!
gliding
soaring
wing flapping
But well explained in section 22.2 Wings and
Flight (pp.404–407) of the text book.
www.liveanimalslist.com
principles for flight
• thrust must equal drag, or a flier will slow down
• lift must equal weight, or a flier will sink
• Bernoulli’s principle: for a wing with a convex
upper surface, air must move faster above the
wing than below, leading to greater pressure
below the wing.
https://www.flight-mechanic.com/aircraft-theory-of-flight/
Gliding – relatively simple
• requires an initial movement (e.g.,
jump) to establish a forward
trajectory
• wing then produces lift by a
combination of downwash (if tilted)
and Bernoulli’s principle (if the
upper surface is convex)
– The wing can never produce quite
enough lift to equal weight, so the
animal slowly sinks
downwash = force that creates lift
Gliding and Soaring
• gliders can maintain constant
speed while slowly sinking
– wing shape and susceptibility to drag
determine ratio of lift to drag forces,
which dictates the angle of descent
(glide angle)
– low glide angle = can travel a long
distance before contacting the ground
– albatross released at an altitude of 1
km could glide ~20 km before contact!
• soaring is when gliders regain
altitude by exploiting air movement,
e.g., updrafts caused by air rising
in the heat of the morning sun
– used by many large vultures
Wandering albatross (Diomedea)
www.dw.com
Turkey vulture (Cathartes)
nature.mdc.mo.gov
Avian Flapping
• must produce thrust and lift with
muscular activity
• thrust produced by movement of
the outer part of the wing, with the
longest feathers (primaries)
• lift produced by the inner part of the
wing (secondaries) acting as an
airfoil (as in gliding, but aided by the
speed resulting from the extra
thrust)
• flapping movements are complex
and adjustable, and cause the flight
feathers of the outer part of the
wing to twist along their length and
act analogously to propellers
Bushtit
(Psaltriparus)
Avian flapping flight - vortices
• major role in flight
– for the individual – create lift, but also drag
– for the group – leading bird’s vortices provide
lift to following birds
snow geese; birdwatching.com
theguardian.com
flight muscles
• downstroke – pectoral major
• upstroke – supracoracoideus muscle
• both insert on the sternum
– these two muscles work in opposite
directions, so why do they insert ventrally on
the same bone?
– ventral mass stabilizes
centre of gravity
https://www.youtube.com/watch?v=aFdvkopOmw0
flight specializations
• larger/heavier birds need longer runs to
takeoff
• landing is tricky! must reduce velocity but
only ‘stall’ at landing – increase pitch of
wing, spread tail to increase drag
– alula – feather-covered second digit is
extended to create lift
https://www.featheredphotography.com/blog/
Other Factors in Flight Performance
• wing loading is mass divided by wing
area (area of wings and body between)
– If too large, flight is impossible
• wing aspect ratio is ratio of wing length
to wing width; a high aspect ratio (long,
narrow wing) has a high lift : drag ratio
• camber is wing curvature, and
contributes to production of lift
• slots between outer wing feathers allow
each to act as an independent airfoil
• different combinations of these factors
are suitable for different types of flight
 wing types in lab
Chiappe et al. 2014, PeerJ 2:e234