do older mothers try harder?
Department of Biology, City University of New York New York, NY 10031, USA Address reprint requests to W.C H. Green, who is now at the Department of Biology, University of Nevada, Reno, NV 89557. ABSTRACT To examine the prediction that reproductive effort should increase with age, I compared female bison (Bison bison) of varying ages in terms of maternal behavior, reproductive costs, and the quality and quantity of offspring. In support of predictions, older mothers showed more tolerance toward and spent more time nursing their calves in months 1 5 than expected based on age differences in size and presumed milk production. The two oldest mothers, who died before calving again, appeared to make the greatest effort. When mothers were barren between calves, which occurred more often in older females, their increased investment enhanced the weight, dominance, maturation rate, and/or fecundity of previous and subsequent offspring. In contrast to predictions, however, offspring quality did
