Suckling and Weaning in Captive White-Tailed and Fallow Deer

Abstract

Abstract Parental investment and parent-offspring conflict theories make specific predictions on the behavior of parents and offspring. Since milk is a direct and vital form of maternal investment in mammals, nursing behavior is very well suited to test such predictions. We provide such tests here, as well as a fine-grained quantitative description of the weaning process in two species of deer. Both in white-tailed and fallow deer, fawns of primiparas had a significantly higher suckling rate than those of multiparous mothers in the first few days of life (2.90 ± 0.70 vs 1.24 ± 0.21 suckles/h from 0 to 5 days in FD, p < 0.01; and 1.42 ± 0.22 vs 0.81 ± 0.08 suckles/h from 6 to 10 days in WTD, p < 0.01). In both species, in the first 10 days of lactation, suckling bouts initiated by the mother had a significantly longer mean duration than those initiated by the fawn. We found no inter-sex difference in the rate of suckling, mean duration of suckles, total time suckling (s/h), and proportion of suckling attempts that were successful, in fawns of both species, at any age from birth to 80 days. White-tailed deer single fawns were identical to twins for all the above parameters. Fallow deer mothers were much more aggressive toward alien fawns than white-tailed deer mothers were, and spent more time close to their fawns (less than 10 m, 38% of the time from birth to 80 days, compared to 12% for white-tailed deer). We propose that weaning starts at about 20 days of age in both species. This is the time when the mother terminates more than half of all suckling bouts, terminates more bouts than she initiates, and when suckles are shorter when she initiates compared to when it is her fawn that does.