Temperature Regulation Gaviiformes Loons (“Divers” in the UK) 5 species Holarctic distribution

Loon’s legs and feet are designed for propelling them through the water. They stand and walk on land with great difficulty. Descendents of an ancient assemblage of seabirds that evolved in the early Tertiary. Loons eat mostly fish and are among the best diving birds. They can reach depths of 75 meters and stay underwater for up to 8 minutes.

“Loons nest in masses of water vegetation, which they pile on small islands or close to the edge of open water.” Gill 2007

Common Loon

Loons use loud yodeling calls on their breeding territories

Pacific Loon

Pacific Loon

Red-throated Loon

Red-throated Loon

Body temperature

Examine behavioral & physiological responses to heat and cold Lecture’s goals Survey avian Tb Examine behavioral & physiological responses to heat and cold

Body Temperature Humans are very precise Tb regulators Normal human Tb is 37ºC Daily 1ºC rhythm, w/ 36ºC late in sleep cycle Human lethal 41ºC (105.8ºF)

Avian Temperature Avian Tb allowed to vary, sometimes widely Measured during rest phase, Tb of most bird species is 40 ± 1.5ºC 1-3ºC higher during active phase Lethal Tb 46-47ºC (116ºF v 106ºF)

Exceptions Penguins 37.0-38.9ºC Ratites 37.8-39.2ºC Procellariiformes 37.5-41.0ºC

Avian Circadian Rhythm 1-3ºC Brown Towhee

Basic principle Large animals have high thermal inertia, it takes the input or loss of a large quantity of heat to change their body temperature

White-crowned Sparrow

Summary Bird Tb higher than human Tb, except for “primative birds” Bird Tb more variable than human Tb Lethal Tb 10°C higher in birds than humans

Regulating body temperature

Birds and mammals are endotherms Cyclodus = Australian Northern Blue-tongue Lizard, Bettongia = Australian rat-kangaroo

Endotherms regulate their Tb by balancing heat gain and heat loss through physiology and behavior Heat gain = Heat loss

Thermal Neutral Zone Within the TNZ, birds change their insulation Postural adjustments fluff up feathers, tuck head and beak, sit on feet Alter blood flow to periphery

Responses to Cold Below Tlc insulation is maximal Linear inc. in heat production Shivering

Responses to heat Above Tlc insulation is minimal panting Above Tlc insulation is minimal Pump out heat via evaporative cooling

Behavioral responses to cold Reduce surface area Seek warmer microclimate

Physiological responses to cold Shivering Hypothermia Torpor

Shivering Below Tlc, all birds shiver Shivering more effective in winter Amer. Goldfinches survive -70ºC for 8 hours in winter, only 1 hr in summer Insulation greater in winter American Goldfinch

Lower Critical Temperature Large birds have relatively less surface area and are thus better insulated Tlc varies with size Emperor Penguin -10ºC Small finch 30ºC

Hypothermia Decreases Tb – Ta gradient and hence need for increased heat production Roadrunner & Turkey Vulture dec Tb to 34ºC at night Boreal Chickadees, at -60ºC, can fly with Tb as low as 30ºC Hypothermia is a fall in Tb below normal temperature.

Roadrunner sunning In morning Roadrunners turn back to sun, raise back feathers exposing the black skin to the sun’s warming rays. Thus they use solar heat to increase their Tb rather than relying on metabolic heat productions. This saves energy.

Ditto Turkey Vultures

Peripheral Hypothermia

Counter Current Heat Exchange

Torpor Profound hypothermia Heart, respiration, and metabolic rates greatly reduced Nightjars, swifts and hummingbirds Torpid Anna’s Hummingbird

Hibernation

Responses to Heat Behavioral Select favorable microclimate Minimize surface area Droop wings Physiological Hyperthermia Inc evaporative water loss (no sweat glands)

Gular Flutter Nonpasserines only All birds pant