Transcript The Insatiable Appetite

The Insatiable Appetite
Costs and Benefits of the High
Metabolic Rate of Birds
Next lectures will cover a bit of physiology – how do you keep an engine running at such high RPMs?
And then seque into the annual cycle of birds. Because resources are not available at constant levels
throughout the year (day length changes, winter, dry & wet seasons in the tropics, etc.), and because
they have such insatiable appetites, birds have scheduling conflicts.
I.
Physiology = metabolism & excretion
High body temperature - ca. 40oC (104oF)
maintained by production of metabolic heat = endothermy
permits use of cold habitats/climates
provides power and endurance needed for flight
requires advanced systems of
heat conservation
heat loss
water economy (evaporative cooling and excretion)
respiration & circulation
waste removal (especially N and CO2)
specifics nerve impulses travel faster
muscles are stronger
but birds need 20-30 x as much energy as similar sized reptile
on fine line where proteins are being denatured
“The Primary Directive”:
Reproduce and survive to reproduce again.
Survival requires:
Eat (and don’t be eaten)
Eating requires:
Being where there’s food - Migration
Having feathers - Molt
• Respiratiory system
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components
nostrils (nares) & nasal
chamber (rete mirabile)
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trachea (syrinx)
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lungs
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air sacs (display in Frigatebirds)
The trick - flow-through lungs
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mammals and herps have dead-end, always
dead air
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birds replace virtually all air in lungs with each
breath
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air intake by sternum
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lower sternum, fill posterior air sacs
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raise sternum, force air into lungs
The Circulatory System
Transports O2 and glucose & fatty acids (fuel)
removes CO2 and other metabolic waste products
The heart
four-chambered (like mammals)
reptiles have 3-chambered-but alligators have 4-chambered
oxygenated blood from lungs
->right atrium/ventricle
systemic blood from system
left atrium/ventricle to lungs
50-100% larger than comparable mammals
output
large proportion goes to legs
more than pectoral muscles! - heat loss?
legs & brain get 10-20% of cardiac output
heat loss and conservation through rete
resting rate 150-300 bpm
lower than some mammals
output higher
heart larger
stroke
more efficient
ventricle empties more
has more, thinner fibers
more mitochondria
Cost: very high blood pressure!
Metabolism
High rates
much heat produced
Temperature regulation
TNZ ca. 18-35 (64-90s)
LCZ lower critical zone/UCZ upper critical zone
•Metabolism
High rates
much heat produced
Temperature regulation
TNZ ca. 18-35 (64-90s)
LCZ lower critical zone
shiver
can’t metabolize brown adipose tissue as mammals do
seek microclimate
evergreens
burrow in snow
cavities (often huddle in groups)
UCZ – upper critical zone
gular flutter
panting - evaporative water loss
controlled hyperthermia
reduces heat loss by decreasing gradient btn body and
environment.
saves water (less lost in evaporative cooling
benefits of running body at higher temperatures
(muscles, nerves)
Why does controlled hyperthermia work?
Insulation & Heat Loss
Hloss = (Tbasal – Tambient)/I
How can a bird manipulate this equation?
Behavior (short & long term)
Structurally (longer term) through molting
Poor insulation = higher metabolic rate
Happy Birthday, Charles!
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Ornithology Today:
Evolution -- both its very existence (Archaeopteryx
lithographica) and its processes - Darwin and Peter &
Rosemary Grant’s studies of Galapagos finches
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Ornithology Today:
Evolution -- both its very existence (Archaeopteryx
lithographica) and its processes - Darwin and Peter &
Rosemary Grant’s studies of Galapagos finches
“There is grandeur in this view of
life, with its several powers,
having been originally breathed
into a few forms or into one; and
that, whilst this planet has gone
cycling on according to the fixed
law of gravity, from so simple a
beginning endless forms most
beautiful and most wonderful have
been, and are being, evolved.”
The last sentence in On The Origin of Species.
I.
Water Economy
Loss through evaporative cooling - especially important in arid regions
Brown Towhee evaporative H20 loss quadruples when ambient
temp goes from 30 to 40oC
Replaced how?
Counter-current mechanisms
Swordfish/Tuna
Fish gills
Controlled hypothermia:
Hummingbirds, vultures, goatsuckers
I.
Water Economy
Loss through evaporative cooling - especially important in arid regions
Brown Towhee evaporative H20 loss quadruples when ambient
temp goes from 30 to 40oC
Replaced how?
Drinking
6O2 + C6H12O6 -> 6CO2 +6H2O (high metabolic rate of birds
results in more metabolic water than comparable
mammals)
food - fruit, prey - Sooty Falcons nest where temp in shade is
49OC (120oF)
I.
Water Economy
Loss through evaporative cooling - especially important in arid regions
Brown Towhee evaporative H20 loss quadruples when ambient
temp goes from 30 to 40oC
Replaced how?
Drinking
6O2 + C6H12O6 -> 6CO2 +6H2O (high metabolic rate of birds
results in more metabolic water than comparable
mammals)
food - fruit, prey - Sooty Falcons nest where temp in shade is
49OC (120oF)
Reduce loss
by countercurrent mech. in nasal chambers
excrete uric acid instead of urea
molecule of uric acid has 2xs the N as one of urea insoluble, flushed out
with less H20 - mammals use 20 times the H20 than birds do to excrete
the same amount of N
Kidneys different - short loops of Henle, so excretion of electrolytes (salts) is not as
efficient.
Salt glands
located above eyes, drain into nasal passage
widespread in non-passerines that have salty diets (mostly marine) - examples?
absent in passerines - not clear why.
enzymatically run (therefore energetically expensive)
may increase resting metabolism by 7%
• Salt Gland
Avian Physiology – Continued & details
Air sacs
9 in most birds (12 in some):
cervical – 2
thoracic – 4
abdominal –2
interclavicular – 1
extends into bones (humerus & sternum)
contacts syrinx,
essential in sound production, heat loss, and cushion internal organs
Furcula – spring-like action helps with movement of sternum & hence air flow.
Retes – nasal cavities have a “temporal” countercurrent as well as a vesicular one.
Metabolic Rates
BMR = Basal metabolic rate—yardstick against which cost of activities can be
measured.
Resting, in TNZ
Activity Metabolism
BMR is rare—almost any activity (slight movements, digestion,
etc.) raises metabolic rate above BMR
Small birds 10-25 times BMR for hours (mammals only 5-10)
Flight is very expensive, but efficient – compare to mammals
Higher per unit time, but you go farther per unit time
Varies with wing shape, flight type—examples?
Egg production, etc.