plz explain to me 'Allen's rule'

In 1877 American Zoologist and Ornithologist Joel Asaph Allen stated a biological rule which says ‘ endotherms from colder climates usually have shorter limbs (or appendages) than the equivalent animals from warmer climates’. This is known as Allen’s rule.

If the surface area of a body is larger, greater amount of heat and energy will be lost. In cold climates it is necessary to conserve heat and energy as much as possible. For this reason according to Allen, the organisms of colder climatic areas have shorter body structures than the warmer climatic areas.