Comparative body composition strategies of breeding and nonbreeding femalecaribou

We evaluated the effects of season and reproductive status on body fat and body protein masses of free-ranging female barren-ground caribou (Rangifer tarandus granti). Body fat mass fluctuated markedly during the year (by a f actor of at least 2) in both reproductive classes, but whereas maximum fatn ess occurred in autumn (September-November) in nonbreeding females, it did not occur until late winter (March-April) in breeding females. Seasonal cha nges in dry body protein mass were relatively modest, with annual maxima av eraging only 31-43% higher than annual minima. Moreover, seasonal differenc es between the reproductive classes were not significant except in November -December. Absolute fat deposition by both breeding and nonbreeding females was highest in summer, though fat deposition increased relative to protein deposition in autumn. Between June and September, the primary deposition o f body protein in breeding females contrasted with the primary deposition o f body fat in nonbreeding females. As a result, breeding females were highl y compromised in their fat deposition but not in their protein deposition, which approximated levels in nonlactating females. Differences in body comp osition between breeding and nonbreeding females were highest in autumn and lowest in early spring because of divergence in summer and convergence in winter.