1. Variation
A difference or deviation in structure or character from others of the same species or group

2. Population
All the individuals of one species in a given area

3. Migration
The seasonal movement of a complete population of animals from one area to another.
Migration is usually a response to changes in temperature, food supply, or the amount of daylight, and is often undertaken for the purpose of breeding

4. Hibernation
An inactive state resembling deep sleep in which certain animals living in cold climates pass the winter.
In hibernation, the body temperature is lowered and breathing and heart rates slow down.
Hibernation protects the animal from cold and reduces the need for food during the season when food is scarce

5. Physiology
The functions and activities of living organisms and their parts

6. Frequency
The Rate at which a repeating event occurs