why big animals stay warmer easier

adapted and amended from: robert bakker pp91-93 dinosour heresies

All thru the animal kingdom, the production of body heat drops in a very regular way as body size increases. But generally, the radiation of heat is less for the large animal.


rabbit = 1 # and elephant = 10,000 #
elephant = 10,000 x heavier
calories / #/ hr

rabbit = 280 & elephant = 28
the elephant produces 10 x less heat per pound per hour -- ( 280 vs. 28)

skin area

rabbit = 75 sq. in per # & elephant = 3.4 per #

so the elephant has 22 x less skin per pound -- ( 75 vs. 3.4 )


compared to the rabbit, the elephant, per pound ---

Biothermal bottom line:
it is easier to chill a mouse than an elephant -- as zoo keepers will attest. Big mammals - even those from tropical homelands - adapt to winter outside in northern zoos better than do small species.

Open the window on a winter day - and the elephant doesn't notice, but the mouse almost immediately begins to shiver and may shiver itself to death within an hour. Shivering is a mammalian mechanism to increase heat production to meet a chilly crisis.

Shivering burns up calories at a rate 5 times the standard metabolism and the tiny mouse can literally burn itself out quite quickly because its body is so small and total amount of body heat is small.

The math expression of this is
Metabolism = k / weight to the -1/4 power

(1) there is 10 times less heat -- ( 280 vs 28 ) but 10,000 times more surface area for the elephant --

and this 10,000 = (1) x (10) x (10) x (10) x (10).

that's where the (10) to the -1/4 power comes to play : (10,000) 1/4 = 1

Australian music quiz:

"what will keep you warmer on a cold nite at the zoo, snuggling up with a 5-ton bull elephant, or with 10,000 bunnies who altogether weigh 5 tons?" hint: remember the singing group called "3 Dog Nite?"

answer: bunny snuggle -- they put out 10x as much heat

But producing less heat per pound actually makes the big animal warmer than the small animal !

The big animal keeps warmer more easily because the area of its skin surface is less, relative to its heat output.

The biothermal bottom line is this: it is easier to chill a mouse than an elephant. Zoo keepers know this. Even big mammals from tropical homelands adapt to winter outside in northern zoos better than do small species. The elephant doesnąt notice the chilly breeze as much as the shivering mouse.

Shivering is the mammalian body's way of increasing heat production to meet the thermal crisis. Shivering burns up the calories at enormous rates, up to five time the standard metabolism, and a shivering mouse literally can burn itself out quite quickly because the body is so small.

the heat of battle

cold blooded animal strategy: -- wait and see what happens - maybe dinner will walk by and i can eat without going 'out'
prey's strategy to stay alive: hide in the cold place

warm blooded animal strategy: always on the move

enzymes: reach peak output within a narrow range of temperatures lizard:
38C = peak operations
28C = 1/2 peak operations
18C = 1/4 peak operations

temperature variables:
time of day
time of year
sun or shade

reptile compensating advantages wait and hit strategy M = k/ W -1/4

m is metabolic heat production
w is body wt
k is a constant
a bunny = 1#
10,000 elephant
the elephants production of body heat is (10,000)1/4 times less per pound or 10x less per pound than that of the bunny producing less heat per pound, however, doesnąt mean a big animal is cold than a small one -- just the reverse.

big reptiles produce less body heat per pound than little ones
big reptiles have much less skin area per pound
giant reps don't chill as quickly as a little one

but a large reptile is always lower metabolism than a mammal --- of the same wt... about 4 times lower

mass homeothermy

this is from physics mysteriers: heat chapter -- about p135
11.) Why do you shiver when you become cold?

Shivering is an involuntary physiological response to a drop in the temperature of air in contact with the body. It is a method that the body uses to increase the rate at which energy is transformed from that stored in the food that was eaten to internal energy of the body by increasing the metabolic rate. The same effect could occur by exercising, which would be a voluntary method of raising the metabolic rate. As pointed out in H. E. Landsberg, Weather and Health, Doubleday, Garden City, New York, 1969, shivering is not a terribly efficient process, since, although it does increase the metabolic rate.