With 5 figures in the text) Ecological conditions, feeding and ranging behaviour as well as physical condition of female Hanuman langurs (Preshytis entellus) were studied in order to analyse the major influences on the timing of reproductive events. The langurs inhabited a semi-evergreen forest dominated by Sal trees (Shorea ?ObUSfC6). The climate was dominated by the summer monsoon lasting from May to September. Availability of plant phytophases was markedly seasonal, with fruiting as well as flushing of the six main food plants during the monsoon. Feeding and ranging behaviour of the females varied with food availability and its distribution. High dietary quality was only obtained during a short period from May to July. Physical condition of the females varied in accordance with dietary quality and energy expenditure, with a good physical condition during the second half of the year. Births occurred from January until June, with most births around the energetically worst period of the year. The results indicate that, in contrast to several other non-human primates, most females of this population gave birth too early to meet the optimum lactation requirements. Complete weaning mainly took place during an energetically bad time of the year (October to December). However, it can be inferred that the reduction of suckling bouts prior to the next conception took place when high quality food was available. Conceptions were confined to the months of July to November, coinciding with the time of best physical condition. Moreover, females who conceived were in a better physical condition than those who failed to conceive, suggesting a primary influence of nutrition on the probability of conception. Seasonality and timing of births may be the result of a regular seasonal shortfall of reSOi,rceS influencing the ability of the females to ovulate and to conceive.

Socio-ecological models aim to predict the variation in social systems based on a limited number of ecological parameters. Since the 1960s, the original model has taken two paths: one relating to grouping patterns and mating systems and one relating to grouping patterns and female social structure. Here, we review the basic ideas specifically with regard to non-human primates, present new results and point to open questions. While most primates live in permanent groups and exhibit female defence polygyny, recent studies indicate more flexibility with cooperative male resource defence occurring repeatedly in all radiations. In contrast to other animals, the potential link between ecology and these mating systems remains, however, largely unexplored. The model of the ecology of female social structure has often been deemed successful, but has recently been criticized. We show that the predicted association of agonistic rates and despotism (directional consistency of relationships) was not supported in a comparative test. The overall variation in despotism is probably due to phylogenetic grade shifts. At the same time, it varies within clades more or less in the direction predicted by the model. This suggests that the model's utility may lie in predicting social variation within but not across clades.

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Reproductive parameters and sexual behavior of free‐ranging Hanuman langurs (Presbytis entellus) were studied over a 13‐year period at Jodhpur, India in a population that breeds throughout the year. Long‐term monitoring of individually identified females living in one‐male‐multi‐female troops revealed a mean cycle length of 24.1 days (n = 113), a mean gestation of 200.3 days (n = 31), menarche at 29.0 months (n = 10), first conception at 35.0 months (n = 12), and a mean birth interval of 16.7 months (n = 114). The loss of unweaned infants accelerated the resumption of menstruation, receptivity, and attractivity; shortened the period between estrus and next conception; and reduced the median birth interval by 20.5%, thus supporting the sexual selection hypothesis of male infanticide. The decline of fertility with age (as measured by the rates of conception per estrus period), a regular postreproductive survival for up to 9 years (which can account for about 25% of a female's life span) and indications for the existence of a “true menopause” support the view that a postreproductive period in langurs is the result of natural selection. There is very limited evidence for situation‐dependent receptivity, because only 7.5% of all estrous days (n = 1,037) fell outside of the mid‐cycle period with at the same time strongly reduced proceptivity and attractivity. Moreover, postconception estrus behavior showed a stereotypical pattern during 31 pregnancies and did not reflect a situation‐dependent response to the immigration of new and potentially infanticidal males. It is likely that females competed for sperm of the harem holder, because the probability of conception increased significantly with an increase in the number of copulations, and when the number of females copulating on the same day decreased. © 1992 Wiley‐Liss, Inc.

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Selection and use patterns of sleeping sites in nonhuman primates are suggested to have multiple functions, such as predation avoidance, but they might be further affected by range defense as well as foraging constraints or other factors. Here, we investigate sleeping tree selection by the male and female members of one group of pileated gibbons (Hylobates pileatus) at Khao Ang Rue Nai Wildlife Sanctuary, Thailand. Data were collected on 113 nights, between September 2006 and January 2009, yielding data on 201 sleeping tree choices (107 by the female and 94 by the male) and on the characteristics of 71 individual sleeping trees. Each sleeping tree and all trees > or =40 cm diameter at breast height (DBH) in the home range were assessed (height, DBH, canopy structure, liana load) and mapped using a GPS. The gibbons preferentially selected tall (mean=38.5 m), emergent trees without lianas. The majority of the sleeping trees (53.5%) were used only once and consecutive reuse was rare (9.5%). Sleeping trees were closer to the last feeding tree of the evening than to the first feeding tree in the morning, and sleeping trees were located in the overlap areas with neighbors less often than expected based on time spent in these areas. These results suggest avoidance of predators as the main factor influencing sleeping tree selection in pileated gibbons. However, other non-mutually exclusive factors may be involved as well.

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