In order to survive, polar bears must keep their body at the right temperature and store enough energy to last through meals that may be days or even months apart.
Literal
Polar-bear [topic-は], live-go for-the-sake-of body [object-を] proper-temperature [at-に] keep, some-days [or-か] several-months might open food [of-の] during endure-[can-られる] amount-[of-だけ] sufficient energy [object-を] store must.
An information-dense scientific sentence. 生きていくために = 'in order to keep living.' 適温に保つ ('maintain at a suitable temperature') uses に for the state to be maintained. 持ちこたえる is a compound for 'to endure, to hold out.' あくかもしれない uses the verb 空く ('to become empty') and かもしれない ('may, might') — 'might have gaps of days or months.' ねばならない is the formal obligation form of なければならない.