why is it that mammals and birds that live at a higher latitude?

Question

why is it that mammals and birds that live at a higher latitude (colder environment) are usually bigger than those of related species that live at a lower latitude?

Answer 1

Maybe they adapted to their environment or they just appear larger because they have more down feathers to stay warm.

Answer 2

This isn't necessarily true. The person who said that never lived in the arctic. Be nice though.

The Arctic Fox is only slightly larger than a large cat. It is the smallest fox. Lemmings are no larger than other rodents. Walrus are not larger than manatees.

The Foxes metabolism enables it to survive. It feeds on artic hares which are simply rabbits. And rabbits which are slight smaller than their Boreal cousins in the south.

The people who postulate the body mass theory only rework a tired theory. Its easier than having to study the topic.

Its a double edged sword. The larger the body mass the greater the need for food. The Black Bear solves this by hibernating. The Great White Bear hunts fat seals on the ice covered arctic seas. Seals are the chocolate candies of prey species.

The problem with that theory is that there simply isn't that much food. The Arctic has what is called a low biomass compared with the Amazon River Basin for instance. So only the Polar Bear. A single species fits that description.

But arctic seals are usually smaller than the fur seals of the north Pacific. So the theory is a myth. What one should realize about the colder areas its not a single strategy that works.

And for the boreal forest. The Red Squirrel is smaller than your city Grey Squirrel. The Red Squirrel spends a limited hibernation. Beaver store food in their dam houses.

The Beaver a swimming rodent is still smaller than the tropical Capybara.

http://en.wikipedia.org/wiki/Capybara

Birds migrate, they don't stick around. So they live both at high and low latitudes. Even penguins migrate. Only one species, the Emperor Penguin stays on land to brood in the Antarctic winter, And they live at a lower higher latitude.

The Arctic Ptarmigan is a pheasant which stays all year around. But it is only a medium size as this reference tells you.

http://en.wikipedia.org/wiki/Ptarmigan

The theory your asking about doesn't stand up under close scrutiny.

One of your teachers needs a refresher course in zoology. And if you have a problem send that teacher this way, with a big grin.

Answer 3

Bigger muscles and bones for mountain climbing, longer hair for warmth retention. And........it's their 'hood.