Respiration and Thermoregulation

4 anatomical structures for bird respiration

• Nostrils

• Tracheal system

• Air sacs 

• Lungs

Avian Lungs

• Avian lungs have no residual volume- every bit of air that goes in will come back out 

• much more efficient than ours 

Avian Air Sacs

• Most birds have 9 air sacs 

• The pressure from the interclavicular sac on the syrinx is going to produce vocalizations so its especially valuable to songbirds 

How do birds breathe in?

• Birds lack a diaphragm 

• Use muscles to lower the sternum which allows the air sacs to expand and then air moves in

Movement of Air Through a Bird:

• First inhalation: In through the posterior air sacs 

• First exhalation: going to the lungs 

• Second inhalation: goes to the anterior air sacs

• Second exhalation: going out of the body 

Why is bird respiration so efficient?

• Maximizes contact of fresh air with the lung surface 

• always have 2 breaths going on at the same time

Physiological structures that maximize lung surface area

Parabronchi

Parabronchi

• hexagonal shape

• The inside is a 3-dimensional network of air capillaries and blood capillaries

• Strong fliers have more parabronchi (~1800) (weak ~400)

  • During flight demand for oxygen increases greatly, breathing rate goes up 12-25X resting

Other Uses for Air Sacs

• Air sacks cool the body during flight 

• Serve as a cushion/buffer for internal organs

Bird Body Temp

• Bird core body temp around 40 celsius (104F) 

  • Regardless of body size or habitat occupied 

  • Higher temp allows for higher metabolism and higher levels of activity 

Endothermy

• costly - birds consume ~20-30X more energy than like-size reptiles

• Maintenance of a high body temp is potentially dangerous because around ~14 celcius proteins in living cells are destroyed more rapidly than they can be replaced (brain damage/cell death)

Endurance

the most important feature of high activity levels

• flying/migration requires lots of endurance 

*high metabolic rate along with red blood cells & oxygen increase the ability to have blood and endurance

Passerine Metabolism

 the basal metabolic rate is slightly higher for them than non-passerines

• Just being awake elevates basal metabolic rate  from 25-80% 

passerines & nonpasserines have about the same daily energy rate and flight metabolism

Swimming & Metabolism

• Swimming mallards increase basal metabolic rate by about 2.5 X 

  • Swimming fast- 6X

Small Birds vs Small Mammal Basal Metabolic Rate

• Small birds can operate at 10-25X basal metabolic rate for many hours 

• Small mammals can only sustain 5-6X basal metabolic rate for just a couple of hours 

Birds at Cold Temps (+example)

tend to have more feathers (in part, might be more down feathers)

• Arctic birds tend to have more down, tropic birds do not 

ex. Willow Ptarmigan

Willow Ptarmigan

• During the winter, willow ptarmigan produce a denser coat of feathers and actually lower basal metabolic rates, which reduces the gradient between internal body temp and external body temp 

  • Like keeping your house at a cooler temp to save money on heating bill, and wearing a sweatshirt instead 

• Both responses to the amount of energy necessary to stay warm 

Birds in Warm Temps

• birds have somewhat of a problem due to their feathers- always carrying insulation

Scholander’s Classic Model of Endothermy

• All animals want to be in the thermoneutral zone in the middle 

• Once you start approaching upper critical temp, you need to cool down (sweating/panting) 

• At lower critical temp, you need to warm up (shiver, put on sweatshirt) 

Responses to Cold (6)

• migrate (leave)

• Bergman’s Rule (increase body size with increasing latitude)

• roost in protective sites (cavities, trees, pocket under snow)

• become hypothermic

• torpor

• tuck feet or bill under wings

Hypothermia Example

chickadees can lower body temp by around 12 Celcius 

Torpor & Example

• More extreme- profound state of hypothermia

  • Ex- hummingbirds

  • Become unresponsive and unable to function normally, O2 use goes down ~75%, body temp goes down up to 32 degrees below normal  

Body Size & Torpor

• Bigger birds cant go into torpor because it takes longer to warm up

  • Hummingbirds only require about an hour to warm back up from a 20 degree torpor, a biggish bird would take about 12 hrs 

    • If its cold, there isn't enough hours daylight for this

Exception to Big Bird Torpor Rule

• Common poorwills go into torpor for several months at a time, often in response to long rainy periods, will even do this during incubation 

  • O2 use gets reduced by around 90%, body temp can be as low as ~ 5 degrees Celsius 

American Goldfinch

• have a significantly higher BMR as measured by O2 consumption when its cold 

• They also have a significantly lower critical temp in the winter time (climatized to the cold)

  • Their critical temp limit increases in the summer, so if there was a major cold snap in the summer they would likely die  

How have we facilitated birds surviving the winter?

bird feeders

Responses to Heat (6)

• hold wings out

• dark plumage (concentrates heat at surface of the wing)

• panting & gular fluttering

• wet their abdomen

• raising feathers & butt to the wind to dissipate heat

• rete mirabile

Rete mirabile

“wonderful net” system in legs

• A system of capillaries that is a countercurrent exchange of heat, trying to maintain a temp gradient relative to ambient temperature

• works in heat & cold

  • heat line stops at the feather line- dissipates heat when hot & conserves when cold