Annual cycle of body composition and hibernation in free-living arctic ground squirrels

We monitored a natural population of arctic ground squirrels (Spermophilus parryii kennicottii) on the North Slope of Alaska for seasonal changes in b ody mass and composition and dates of immergence into and emergence from hi bernation. Yearlings and adult females were at the lowest body mass of thei r active season at emergence in spring. Their mean body mass did not increa se for 1 month after emergence and peaked in July (adult females) and Augus t (yearlings). Body mass of adult males was near the highest of the active season when they emerged from hibernation and decreased by 21% over the sub sequent 10-day mating season. Juveniles gained body mass during their activ e season, except for significant losses associated with dispersal. During h ibernation, females lost >30% of their body mass, but adult males emerged i n spring without significant decreases in body mass, fat, or lean. Yearling and nonreproductive males were significantly lower in fat but not lean mas s at emergence than immergence, and females were significantly lower in fat and lean mass. Arctic ground squirrels entered hibernation over a >1-month interval beginning in early August; females entered before males, and adul ts of each sex immerged before juveniles. Reproductive males emerged before females, and fatter females emerged significantly earlier than leaner fema les. Vaginal estrus was maximal at 3 days post-emergence. Nonreproductive m ales emerged last from hibernation. Mean +/- SE days in hibernation was 240 .1 +/- 12.1 for adult females (69% of the year), 235.8 +/- 10.3 for juvenil e females, 230.3 +/- 4.2 for nonreproductive males, 220.3 +/- 12.5 for adul t males, and 214.7 +/- 6.5 for juvenile males. Timing of immergence into an d emergence from hibernation for arctic ground squirrels did not differ sig nificantly from sciurid populations in temperate latitudes.