1990 1992 1994 1996 1998 2000 2002 Year
Figure 21.3. Proportion of births each year being produced by captive-born or wild-caught parents. o, wild-caught parents; •, captive-born parents.
In fact, in 2001 for the first time more offspring were produced from captive-born parents (one or both captive born) than wild-born counterparts (one or both parents wild-born; see Fig. 21.3). However, this finding does not consider the different number of breeding-age individuals in the two groups. On a 'per-panda basis', average fecundity (number of births to parents in a group per number of breeding-age animals in a group, averaged over both sexes) does not differ between wild-born and captive-born parents (paired Student's t-test; d.f = 10; t = 1.796; p — 0.20; Fig. 21.4). Although fecundity has increased in both groups since 1990, the improvement has only been statistically significant in the wildborn giant pandas (see Fig. 21.4). Overall, it seems that captive-born giant pandas are capable of reproducing at the rate of their wild-born counterparts, although substantial year-to-year variation remains.
Figure 21.5 illustrates the age-specific fecundity patterns from all reproductive events since 1990. Fecundity rates are calculated separately for males and females. Each birth attributes 0.5 of that birth to each parent so that, for example, female mx — number of births to females at age x multiplied by 0.5 divided by the number of females of age x. This functionally assumes an equal sex ratio at birth and attributes all reproductive events to both the sire and dam. The points have been smoothed with the Brass function (Gage, 2001). Since data on opportunity to breed are not recorded in the studbook, these distributions represent observed fecundity patterns given historical management practices and do not portray maximum potential fecundity. Additionally, wild-born fecundity data are approximate because the
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