Estrus (also known as Heat) is a type of biological period for the female Keidrans, that affects many male Keidrans (and maybe Basitins) that are near a female in estrus. The symptoms and frequency of this phase depends on the type of Keidran it effects. For instance, Wolf Keidran only go into estrus twice, usually in the Fall and more intensely in Spring. The Tiger Keidran may experience it several times a year and exhibit much lighter effects than the wolves. Known effects include anxiety, mood swings, snappy aggression, increased attraction to the opposite sex, and headaches. Estrus in spring time is notorious in all Keidran species.