Captive and wild orangutan (Pongo sp.) survivorship: a comparison and the influence of management.

For managers of captive populations it is important to know whether their management provides a species with the physical and social environment that maximizes its survivorship. To determine this, survivorship comparisons with wild populations and long-term evaluations of captive populations are important. Here we provide both for orangutans. We show that survivorship has increased during the past 60 years for captive orangutan populations in zoos. In addition, we show that survivorship of captive orangutans in the past used to be lower than for wild orangutans, but that for recently born (1986-2005) orangutans survivorship is not significantly different from the wild. This indicates that captive management in the past was suboptimal for orangutan survivorship, but that modern management of captive orangutans has increased their survivorship. We discuss the possible factors of modern management that could have influenced this.

Life history of wild Sumatran orangutans (Pongo abelii).

We present life history data on wild Sumatran orangutans gleaned from a 32-year and a 5.5-year study. Estimated age at first reproduction was 15.4 years. At 9.3 years, the average interbirth interval for this population is the longest ever recorded for any great ape population, significantly longer than that of a Bornean orangutan population. We find that age-specific mortality of Sumatran orangutans does not differ between sexes and is significantly lower than that of wild chimpanzees. We conclude that orangutan life history is the slowest among extant great apes. In accordance with their slow life history, longevity in the wild is estimated to be at least 58 years for males and at least 53 for females. We find no evidence for menopause. These data suggest that compared to the ancestral state, humans have undergone less of an increase in longevity than commonly assumed, and have experienced selection on earlier cessation of reproduction.

Possible audience effect in Thomas langurs (Primates; Presbytis thomasi): an experimental study on male loud calls in response to a tiger model.

Recent research indicates that animal vocalizations can refer to objects in the outside world, and that call production may be controlled by the sender depending on the type of audience involved. Our research on wild male Thomas langurs (Primates: Presbytis thomasi) shows that these males call as a response to a tiger model when they are in a group, but do not call when they are solitary. This is the first experimental study on wild primates to demonstrate that the presence or absence of an audience influences calling behavior. Our results indicate that males in mixed-sex groups give more loud calls than solitary males when exposed to a predator model. This suggests that giving loud calls in response to predators is not purely a reflex and may be controlled in some way by the sender.

Measuring fruit patch size for three sympatric indonesian primate species.

Food availability is one of the basic factors affecting primate density and socioecology, but food availability is difficult to assess. Two different ways to obtain accurate estimates of food availability have been proposed: using phenology data or using the behaviour of animals. Phenology data can be refined by only including trees that are large enough to be used; including (potential) tree species in which by the concerned primate species forage; or including (fruiting) trees of these species that actually produce fruit. Alternatively, the sizes of the actually visited trees (foraging trees) give an estimate of fruit availability. These measures are compared for three sympatric primate species at the Ketambe Research Station, Sumatra, Indonesia: the Thomas langur, the long-tailed macaque and the orangutan. The sizes of fruiting trees and the foraging trees are larger than the potential trees. The sizes of the potential trees and of the fruiting trees are similar for the three primate species. This, however, is not reflected in the use of trees: the langurs forage on average in trees of similar size to those producing fruit, whereas the macaques and orangutans forage in trees larger than those producing fruit. The use of trees does not necessitate a different cut off point of included dbhs for the three compared primate species. The use of trees of different sizes, however, may be regulated by food competition. This indicates that sympatric primates make different foraging decisions and that behavioural measures of food availability will be less reliable.

Arthrokinetic and vestibular information enhance smooth ocular tracking during linear (self-)motion.

We studied the gain of smooth ocular tracking for visual, vestibular and arthrokinetic cues, in combination as well as separately, in order to examine how these multisensory cues influence tracking performance. By use of motion along a linear track (besides the self-evident visual influence) evidence was found for arthrokinetic and vestibular enhancement of smooth ocular tracking. These results were in close correspondence with the results of our former study about arthrokinetic influence on linear self-motion perception. Therefore, we conclude that information from the limbs about linear (self-)movement has analogous characteristics and generates analogous responses to the information about angular (self-)movement.