Geissmann, T. and Orgeldinger, M. (1995). Neonatal weight in gibbons (Hylobates spp.). American Journal of Primatology 36: 179-189.
T. Geissmann1 and M. Orgeldinger2
1Anthropological Institute, University Zürich-Irchel, Switzerland
2Zoological Garden Frankfurt/Mainand Zoological Institute, Ruprecht-Karls-University,
Heidelberg, Germany
Key words: Birth weight; neonatal weight; Cesarian section; neonatal death;
premature birth; twins; Hylobatidae.
Abstract: Neonatal and birth weights of gibbons have mostly been reported
for single individuals, and larger samples (n = 2 - 8) have apparently been published
for only two species of gibbons (Hylobates lar and H. syndactylus).
In addition, a critical examination of the few published neonatal weights of gibbons
shows that several of them should not be used. Neonatal weights are here defined
as weights taken on infants up to seven days old, whereas birth weights include only
those taken on the day of birth. This paper presents neonatal weights for 6 representative
species of gibbons (H. lar, H. leucogenys, H. moloch, H. muelleri, H. pileatus,
H. syndactylus) and some of their hybrids. Most of our data stem from surviving
animals that were subsequently hand-reared and include 80 infants, thus making the
previously available dataset 5 times larger. Our neonatal weights fall roughly into
3 different classes: neonates of the lar group (about 390 g, n = 27), the
concolor group (about 510 g, n = 7), and the siamang (about 540 g, n = 46).
This grouping corresponds not only to taxonomic units within the hylobatids, but
also to grouping of gibbons by adult body weight. No weight difference between males
and females is evident in our sample, and hybrids of the lar group do not
appear to differ in weight from pure species. True birth weights (i.e., weights recorded
on the day of birth) are available for only a few individuals. These weights are,
on average, 7% higher than neonatal weights, but the difference is not statistically
significant. Additional samples of neonatal weights suggest that infants that die
on the day of birth weigh, on average, 17% less, twins weigh 29% less, and infants
born by Cesarean section weigh 19% more than our reference sample of neonates.
Site by Thomas Geissmann.
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