Seasonality, body condition, and timing of reproduction in Propithecus verreauxi verreauxi in the Kirindy Forest.

Mammals that live in seasonal environments may adjust their reproductive cycles to cope with fluctuations in food availability. Because lemurs in Madagascar experience highly seasonal variation in food availability, we examined the effects of fluctuating food availability on body condition and reproduction in one of the larger living species, Verreaux's sifaka (Propithecus verreauxi verreauxi), in the Kirindy Forest of western Madagascar. Seven years of demographic data were combined with an intensive study of 25 individuals over the course of 18 months. In contrast to other populations of Verreaux's sifaka, females were found to have greater body mass than males. Both male and female sifaka exhibited significant losses of body mass and fat during the dry season. Females were more likely to give birth and successfully wean an infant when they had higher body mass during the mating season. They mated during the periods of high and declining food availability, gave birth during the lean season, and then timed mid/late lactation with the period of increasing food availability. Thus, we conclude that sifaka follow the "classic" reproductive strategy (sensu van Schaik and van Noordwijk [Journal of Zoology (London) 206:533-549, 1985]).