▁movements ▁of ▁the ▁E tr us can ▁sh rew ▁are ▁rapid , ▁with ▁a ▁rate ▁of ▁about ▁ 7 8 0   min − 1 ▁( 1 3   s − 1 ). ▁In ▁cold ▁seasons ▁and ▁during ▁short ages ▁of ▁food , ▁the ▁sh rew s ▁lower ▁their ▁body ▁temper atures ▁down ▁to ▁about ▁ ▁and ▁enter ▁a ▁state ▁of ▁temporary ▁hi bern ation ▁to ▁reduce ▁energy ▁consumption . ▁Rec overy ▁from ▁this ▁state ▁is ▁accompanied ▁by ▁sh iver ing ▁with ▁the ▁frequency ▁of ▁about ▁ 3 5 0 0   min − 1 ▁( 5 8   s − 1 ). ▁This ▁indu ces ▁he ating , ▁with ▁the ▁rate ▁up ▁to ▁ 0 . 8 3   ° C / min , ▁which ▁is ▁among ▁the ▁highest ▁values ▁recorded ▁in ▁m amm als ; ▁the ▁heart ▁rate ▁increases ▁expon entially ▁with ▁time ▁from ▁ 1 0 0 ▁to ▁ 8 0 0 – 1 2 0 0   be ats / min , ▁and ▁the ▁resp ir atory ▁rate ▁r ises ▁linear ly ▁from ▁ 5 0 ▁to ▁ 6 0 0 – 8 0 0   be ats / min . ▁ ▁E tr us can ▁sh rew s ▁mate ▁primarily ▁from ▁March ▁to ▁October , ▁though ▁they ▁can ▁be ▁pre gn ant ▁at ▁any ▁time ▁of ▁the ▁year . ▁P airs ▁usually ▁form ▁in ▁the ▁spring ▁and ▁may ▁toler ate ▁each ▁other ▁and ▁their ▁young ▁for ▁some ▁time ▁at ▁the ▁nest . ▁The ▁gest ation ▁period ▁is ▁