VARIABILITY IN MATERNAL-BEHAVIOR BY DALLS SHEEP - ENVIRONMENTAL TRACKING OR ADAPTIVE STRATEGY

Effects of environmental variation and timing of births on patterns of nursing and weaning behaviors were examined in Dall's sheep (Ovis dal li dalli) in central Alaska. Indices of plant productivity, growing se ason, and quality of diet (crude protein in feces) indicated that late r plant phenology resulted in a shorter growing season in 1989. Timing of parturition was ca. 2 weeks later and less sychronous in 1989 than in 1988. Females responded to this delay of births, and to forage ava ilability and quality, by nursing lambs for a greater total time follo wing parturition, and by reducing total time spent nursing more rapidl y in 1989. Maternal females exhibited behaviors associated with weanin g more often during early lactation in 1989, when parturition was dela yed. Patterns of maternal care did not correspond with indices of qual ity of diet, suggesting that these differences did not result from env ironmental tracking. At far northern latitudes, where the period in wh ich to rear young is limited, females exhibited plasticity in patterns of maternal investment to compensate for variation in environmental c onditions and timing of births. This variability in maternal care like ly represents an adaptive strategy important even in highly predictabl e environments with only slight or occasional annual variation.