Seasonality of reproduction in wild cotton-top tamarins (Saguinus oedipus) in Colombia.

Seasonal availability of resources can influence the timing and success of reproduction in primates. This study examines the annual pattern of conceptions, mid-term (13 weeks) and full-term (26 weeks) pregnancy losses, births, and infant survivorship of the Critically Endangered cotton-top tamarin (Saguinus oedipus) at Proyecto Tití's long-term field site in Santa Catalina, Colombia. Using 18 years of behavior, physical exam, and fecal steroid data (N = 51 females, 168 conceptions, 121 liters), fecal estrone conjugate (E1 C) and pregnanediol-3-glucuronide (PdG) or progesterone (P4) profiles were examined to investigate the relationships between female reproductive patterns and reproductive success with feeding and climatic data. Cotton-top tamarins demonstrated seasonal patterns of reproduction and pregnancy losses. We found positive correlations between peak conception and nectarivory, births and rainfall, and mid-lactation and frugivory. High body mass mothers reproducing during the peak season were more likely to have infants survive. Overall, these results suggest that tamarins use a "relaxed income-breeder" strategy. Cotton-top tamarins appear to maximize reproductive output at the time of ovulation, and can reduce their investment in the current reproductive effort at many stages. Changes in food availability due to habitat loss and climate change will require the Critically Endangered cotton-top tamarins to alter their reproductive strategies to survive.

Biotic and abiotic drivers of dispersion dynamics in a large-bodied tropical vertebrate, the Western Bornean orangutan.

Understanding of animal responses to dynamic resource landscapes is based largely on research on temperate species with small body sizes and fast life histories. We studied a large, tropical mammal with an extremely slow life history, the Western Bornean orangutan (Pongo pygmaeus wurmbii), across a heterogeneous natural landscape encompassing seven distinct forest types. Our goals were to characterize fluctuations in abundance, test hypotheses regarding the relationship between dispersion dynamics and resource availability, and evaluate how movement patterns are influenced by abiotic conditions. We surveyed abundance in Gunung Palung National Park, West Kalimantan, Indonesia, for 99 consecutive months and simultaneously recorded weather data and assessed fruit availability. We developed a Bayesian hierarchical distance sampling model to estimate population dispersion and assess the roles of fruit availability, rainfall, and temperature in driving movement patterns across this heterogeneous landscape. Orangutan abundance varied dramatically over space and time. Each forest type was important in sustaining more than 40% of the total orangutans on site during at least one month, as animals moved to track asynchronies in fruiting phenology. We conclude that landscape-level movements buffer orangutans against fruit scarcity, peat swamps are crucial fallback habitats, and orangutans' use of high elevation forests is strongly dependent on abiotic conditions. Our results show that orangutans can periodically occupy putative-sink habitats and be virtually absent for extended periods from habitats that are vitally important in sustaining their population, highlighting the need for long-term studies and potential risks in interpreting occurrence or abundance measures as indicators of habitat importance.

Responses to Spatial and Temporal Variation in Food Availability on the Feeding Ecology of Proboscis Monkeys (Nasalis larvatus) in West Kalimantan, Indonesia.

Folivorous primates have long been assumed to experience food competition less acutely than frugivores due to their ability to eat leaves, an abundant resource in most forest systems. Consequently, the behavioural responses of leaf-eating primates to variation in food availability are less well characterised than those of frugivores. Recent empirical studies have demonstrated that many colobine species are more affected by food availability and distribution than previously thought; they employ multiple strategies to survive during periods of food scarcity. We studied a population of proboscis monkeys (Nasalis larvatus) over 16 months in three forest types in West Kalimantan, Indonesia, to examine their responses to temporal fluctuation and spatial variation in food availability. We examined how feeding behaviour was influenced by the availability of plants in botanical plots to identify important and preferred foods of proboscis monkeys across months and in different forest types. Proboscis monkeys consumed foods from 68 genera, comprising 35% young leaves, 27% unripe fruit, 12% flowers and 6% mature leaves. Consumption of plant parts and genera by proboscis monkeys varied in response to monthly changes in food availability but did not vary among forest types despite substantial differences in phenology and floristics among them. The monkeys preferred unripe fruits and flowers and used young and mature leaves as fallback foods in mangrove forests. Documentation of proboscis monkey responses to variation in food availability contributes to our understanding of how monkeys respond to changes in their environments due to climate change and habitat degradation.

Dietary diversity, feeding selectivity, and responses to fruit scarcity of two sympatric Bornean primates (Hylobates albibarbis and Presbytis rubicunda rubida).

Effectively characterizing primate diets is fundamental to understanding primate behavior, ecology and morphology. Examining temporal variation in a species' diet, as well as comparing the responses of different species to variation in resource availability, can enhance understanding of the evolution of morphology and socioecology. In this study, we use feeding data collected over five years to describe the diets of two sympatric Southeast Asian primate species of similar body size: white-bearded gibbons (Hylobates albibarbis) and red leaf monkeys (Presbytis rubicunda rubida), in Gunung Palung National Park, West Kalimantan, Indonesia. Long-term data sets are especially important for characterizing primate diets in Southeast Asia, where the forests exhibit supra-annual mast fruiting events. We found that gibbons were mainly frugivorous, with fruit and figs comprising 70% of their 145 independent feeding observations, whereas leaf monkeys ate a substantial amount of seeds (26%), fruits and figs (26.5%) and leaves (30%, n = 219 independent feeding observations). Leaf monkeys consumed a higher number of plant genera, and this was due mostly to the non-frugivorous portion of their diet. To investigate resource selection by these primates we utilized two different approaches: the Manly Selectivity Ratio, which did not take into account temporal variation of resource availability, and a model selection framework which did incorporate temporal variation. Both species selected figs (Ficus) more than predicted based on their availability under the Manly Selectivity Ratio. Model selection allowed us to determine how these primates alter the proportion of leaves, flowers, seeds, figs and fruit in their diets in response to variation in fruit availability. When fruits were scarce, both gibbons and leaf monkeys incorporated more leaves and figs into their diets, indicating that these two food classes are fallback foods for these primates. We discuss how different measures of resource selection can provide seemingly contradictory results, and emphasize the importance of long term studies that combine independent feeding observations with rigorous assessment of temporal variation in resource availability when modelling feeding selectivity.

An Assessment of the Population of Cotton-Top Tamarins (Saguinus oedipus) and Their Habitat in Colombia.

Numerous animals have declining populations due to habitat loss, illegal wildlife trade, and climate change. The cotton-top tamarin (Saguinus oedipus) is a Critically Endangered primate species, endemic to northwest Colombia, threatened by deforestation and illegal trade. In order to assess the current state of this species, we analyzed changes in the population of cotton-top tamarins and its habitat from 2005 to 2012. We used a tailor-made "lure strip transect" method to survey 43 accessible forest parcels that represent 30% of the species' range. Estimated population size in the surveyed region was approximately 2,050 in 2005 and 1,900 in 2012, with a coefficient of variation of approximately 10%. The estimated population change between surveys was -7% (a decline of approximately 1.3% per year) suggesting a relatively stable population. If densities of inaccessible forest parcels are similar to those of surveyed samples, the estimated population of cotton-top tamarins in the wild in 2012 was 6,946 individuals. We also recorded little change in the amount of suitable habitat for cotton-top tamarins between sample periods: in 2005, 18% of surveyed forest was preferred habitat for cotton-top tamarins, while in 2012, 17% percent was preferred. We attribute the relatively stable population of this Critically Endangered species to increased conservation efforts of Proyecto Tití, conservation NGOs, and the Colombian government. Due to continued threats to cotton-top tamarins and their habitat such as agriculture and urban expansion, ongoing conservation efforts are needed to ensure the long-term survival of cotton-top tamarins in Colombia.

Sleeping site selection by proboscis monkeys (Nasalis larvatus) in West Kalimantan, Indonesia.

Primates spend at least half their lives sleeping; hence, sleeping site selection can have important effects on behavior and fitness. As proboscis monkeys (Nasalis larvatus) often sleep along rivers and form bands (aggregations of one male groups) at their sleeping sites, understanding sleeping site selection may shed light on two unusual aspects of this species' socioecology: their close association with rivers and their multilevel social organization. We studied sleeping site selection by proboscis monkeys for twelve months at Sungai Tolak, West Kalimantan, Indonesia to test two main hypotheses regarding the drivers of sleeping site selection: reduction of molestation by mosquitoes and anti-predator behavior. We identified to genus and collected data on the physical structure (diameter at breast height, relative height, branch structure, and leaf coverage) of sleeping trees and available trees in three forest types. We used resource selection function models to test specific predictions derived from our two hypotheses. The monkeys preferred to sleep in large trees with few canopy connections located along rivers. The selection of large emergent trees was consistent with both of our main hypotheses: decreased molestation by mosquitoes and reduced potential entry routes for terrestrial predators. Although we are only beginning to understand how sleeping sites might influence behavior, grouping, and potential survival of this species, our study has shown that proboscis monkeys (at Sungai Tolak) have a very strong preference for large trees located near the river. As these trees are often the first to be logged by local villagers, this may exacerbate the problems of forest loss for these endangered monkeys.

Defining fallback foods and assessing their importance in primate ecology and evolution.

Physical anthropologists use the term "fallback foods" to denote resources of relatively poor nutritional quality that become particularly important dietary components during periods when preferred foods are scarce. Fallback foods are becoming increasingly invoked as key selective forces that determine masticatory and digestive anatomy, influence grouping and ranging behavior, and underlie fundamental evolutionary processes such as speciation, extinction, and adaptation. In this article, we provide an overview of the concept of fallback foods by discussing definitions of the term and categorizations of types of fallback foods, and by examining the importance of fallback foods for primate ecology and evolution. We begin by comparing two recently published conceptual frameworks for considering the evolutionary significance of fallback foods and propose a way in which these approaches might be integrated. We then consider a series of questions about the importance of fallback foods for primates, including the extent to which fallback foods should be considered a distinct class of food resources, separate from preferred or commonly eaten foods; the link between life history strategy and fallback foods; if fallback foods always limit primate carrying capacity; and whether particular plant growth forms might play especially important roles as fallback resources for primates. We conclude with a brief consideration of links between fallback foods and primate conservation.