I. Adaptations for flight:
A. severe constraints imposed by the physics of flight means that flighted birds are all very similar (makes systematics diff.)
B. Weight vs. Energy - principal adaptations reduce weight and increase efficiency (explains lack of herbivorous birds) weight loss:
1. Pneumaticized bones and feathers (Frigatebird’s feathers probably weigh more than the whole bird)
and airsacs
Loss of bones and fusion
skull
bones fused and lost (jaws)
trade teeth for horny sheath of bill
limbs
vertebrae - pygostyle
Reproductive tract
females have only 1 ovary
males - testes reduced in non-breeding season (4 - 500 xs)
move principal wing elevators below center of grav.
strength
fusion throughout skeleton
Synsachrum
hand - loss of digits and fusion
2 rather than 10 wrist bones
3 rather than 5 digits
leg - tibiotarsus/tarsometatarsus
uncinate processes - reinforce ribcage against stress from flight muscles
furcula - spring-like action of unknown function, may act as bellows to move air through air sacs?
fuel efficiency
four-chambered heart
flow-through lungs
“dark meat” - capable of extreme aerobic metabolism
narrow cells - high surface to volume ratio for O2 absorption
lots of myoglobin & mitochondria
fat and enzymes for aerobic metabolism
“white meat”
capable of a few very powerful contractions
little myoglobin
anaerobic metabolism
different enzymes
tire as lactic acid accumulates
II. Evolution of feathers:
what is a feather?
Dead Keratin in a protein matrix
keratin an inert fibrous substance
found in claws, nails, etc. (but different chemistry)
where did they come from? Reptilian scales (but chemistry is different)
why did they appear? what benefit did they convey?
Thermoregulation?
keep heat in
were dinosaurs warm-blooded?
Bakker says yes
Feduccia says no way
keep heat out
modern examples
Other functions
aerodynamics
insulation
communication & camouflage
sound production
hearing
protection
water repellency
water transport
tactile sensation
protection (cassoaries have “brush pants”)
support
originally living,
blood feathers
grow from follicles
“hunger” bars
Shaft
Calamus - quill
rachis
Vanes
Barbs
ramus
barbules (=velcro)
barbicel
downy portion (lacks barbicels)
aftershaft
Primaries usually 10 remix/remiges
rarely much modified - aerodynamics too important
secondaries
6 hummers - 40 albatrosses
come off ulna
sometimes modified - see text p. 71 Standard-winged Nightjar
tail - retrix/retrices
off pygostyle
usually 12, but can be 24 (snipe - some for sound)
down feathers
insulation
usually no rachis and no barbicels
filoplumes - sensory
Bristles
protection
also sensory
Feather tracts
thousands of feathers
swan 25,000 - feathers, 20000 on head and neck
songbirds 2-3000 feathers, 30-40% on head and neck
can weigh 2-3 times the skeleton
Bald Eagle - feathers 17% of mass, skeleton 7%
most birds have tracts, some don’t (ostriches)
feather tracts pterylae
non-feathered tracts apteria
8 major pterylae seperated by apteria
not fully understood
facilitate muscular control?
facilitate limb movements?
Feather care
Oil or preen gland
oil of waxes, fatty acids, fat & water
clean feathers
maintain moisture and flexibility
unique in passerines
preening
rearrange
de-louse
scratch head
Molt and plumages
natal down
replaced by pennaceous feathers in juvenal plumage
body molt into immature or
adult plumage
Feathers dead -
no blood, muscles or nerves
can change only by abrasion or fading, or molt
starlings lose spots
meadowlarks expose bright yellow and black ventral feathers
growth of new feathers
epidermal and dermal cells at base of feather follicle
rapid growth - 7mm/day in raptors ca. 1”/3 days
pushes old feather out
growing feather keratinized at tip first, breaks out of sheath
pulp of feather reabsorbed by follicle
feather held in follicle by muscle and friction
fright molt
replace pulled feathers
normal molt.
Molts and plumage
why molt? - feathers wear out - structural and fade
natal down
varies with families
some spp. have much, others little
some have more than one coat - sometimes from different follicles
juvenal plumage replaces down
young is now a juvenile
juvenal plumage replaced by immature or adult in next molt
flight feathers not always replaced
molt sequences
plumages
juvenal
basic - non breeding
alternate - breeding
molts - pre-each
feathers replaced in sequence within a feather tract - we don’t know how? differential sensitivity to hormones?