Lecture 3
Avian Adaptations
Chapters 4-6 in Gill
Why are birds birds?
Common Loon
Laysan Albatross
American White Pelican
Great Blue Heron
Roseate Spoonbill
Red-tailed Hawk
MN Volunteer 2006
Painted Bunting
Birds are Adapted for:
1. Weight reduction while retaining
skeletal strength
2. Power
3. Balance
Weight Reduction
1. light skeleton relative to body
weight
–
–
hollow bones
reinforced
Weight Reduction
2. networked bones
3. truss-like structure - pectoral
girdle - a tripod of bones
(scapula, coracoid, and clavicle)
Pectoral Girdle
Note: Responsible for terms in red
Weight Reduction
4. fusion of finger bones (metacarpals) - 2
missing and 2 fused, thumb supports the
alula, wrist bones (carpals) reduced to 2
Wing and Alula
Weight Reduction
5. reduction of tail to a pygostyle
Weight Reduction
6. flattening of sternum - carina for
flight muscles
Birds are Adapted for:
1. Weight reduction while retaining
skeletal strength
2. Power
3. Balance
Birds are Adapted for:
1. Weight reduction while retaining
skeletal strength
2. Power
3. Balance
Balance Adaptations
1. center of gravity through reduced
skull size and bulk just below the
wings
2. fusion and elongation of pelvic
girdle to support upper weight,
but also for walking
Note how far
back pelvic
girdle is placed
Balance Adaptations
3. liver is on right to match single
ovary on left
4. wide separation of legs to aid in
egg-laying
5. general streamlining
Skeletal System
1. Function
a. Support
b. Protection - e.g., of internal
organs
c. Articulation - e.g., of muscles
d. Manufacture of blood corpuscles
e. Calcium storage
Skeletal System
2. Modifications
a. Pectoral girdle
•
•
•
•
scapula - thin, blade-like, long in
strong fliers
coracoid - stout bone
furcula - 2 clavicles (or wishbone)
sternum
Skeletal System
2. Modifications
b. Pelvic girdle
•
•
•
•
Synsacrum
evolution toward fusion - early
archosaurian reptiles, pelvic bones
radiate outward from acetabulum
like 3 spokes-ilium, ischium, and
pubis
long and narrow in walking birds
short and wide in flying birds
Pelvic Girdle
Note: Responsible for terms in red
Skeletal System
2. Modifications
c. Fused bones - especially in the
hand and vertebrae
Skeletal System
2. Modifications
d. Sclerotic ring
Transverse Section Thru
Eye
Skeletal System
2. Modifications
e. Single condyle - provides greater
neck flexibility; some “hand”
functions performed by the bill
f. Hyoid apparatus - allows great
extension of the tongue in
hummingbirds and woodpeckers
e.g., up to 4x length of bill
Hyoid Apparatus
Hyoid Apparatus
Northern Flicker
Skeletal System
2. Modifications
g. Vertebral column - vertebrae
varies from 39 to 63
• most vertebrae are fused
• ribs (double articulation) uncinate
processes increased support and
strength both for flying and diving
(e.g., loons the process extends
across two adjoining ribs) - bones
are "thin, flat"
Skeletal System
2. Modifications
h.
•
•
•
Legs - femur is short and flat
tibia – drumstick
fibula - very small, splinter bone
tibiotarsus – the entire bone
including the tibia and proximal
fused tarsal bones
Skeletal System
2. Modifications
i. Toes
•
•
Generally 4 toes
First is usually directed backward (hallux)
Skeletal
System
Legs
National Wildlife Federation –
Award Winning Pictures –
2005?
Ancestral California Condor