Ecological and Behavioural Factors Influencing Territorial Call Rates for the Bolivian Titi Monkeys, Plecturocebus modestus and Plecturocebus olallae.

Primate territorial calls have been used to locate groups in censuses. Daily variations in call rates are a potential source of error in these studies. To obtain more accurate estimations of population density it is necessary to determine how much variation there is in group call rates and to identify the factors that influence them. We present data on the emission of territorial calls by two threatened and endemic titi monkeys in Bolivia: Plecturocebus olallae and P. modestus. We found interspecific differences in daily call rates (52% P. modestus and 33% P. olallae). Groups inhabiting more continuous forests vocalized more frequently than groups in fragmented forests, which might be linked to the higher abundance of groups in less fragmented forests. We found seasonal differences in call rates between species, with more frequent calling in P. modestus during the dry season, while P. olallae called more frequently in the rainy season. The study groups emitted territorial calls mostly from the central zones of their territories, suggesting they do not face intense spatial competition with neighbouring groups. Our results improve the general ecological knowledge on P. olallae and P. modestus, and can also be used to improve population abundance studies and ongoing conservation efforts.

Determinants of spatial behavior of a tropical forest seed predator: The roles of optimal foraging, dietary diversification, and home range defense.

Specialized seed predators in tropical forests may avoid seasonal food scarcity and interspecific feeding competition but may need to diversify their daily diet to limit ingestion of any given toxin. Seed predators may, therefore, adopt foraging strategies that favor dietary diversity and resource monitoring, rather than efficient energy intake, as suggested by optimal foraging theory. We tested whether fine-scale space use by a small-group-living seed predator-the bald-faced saki monkey (Pithecia irrorata)-reflected optimization of short-term foraging efficiency, maximization of daily dietary diversity, and/or responses to the threat of territorial encroachment by neighboring groups. Food patches across home ranges of five adjacent saki groups were widely spread, but areas with higher densities of stems or food species were not allocated greater feeding time. Foraging patterns-specifically, relatively long daily travel paths that bypassed available fruiting trees and relatively short feeding bouts in undepleted food patches-suggest a strategy that maximizes dietary diversification, rather than "optimal" foraging. Travel distance was unrelated to the proportion of seeds in the diet. Moreover, while taxonomically diverse, the daily diets of our study groups were no more species-rich than randomly derived diets based on co-occurring available food species. Sakis preferentially used overlapping areas of their HRs, within which adjacent groups shared many food trees, yet the density of food plants or food species in these areas was no greater than in other HR areas. The high likelihood of depletion by neighboring groups of otherwise enduring food sources may encourage monitoring of peripheral food patches in overlap areas, even if at the expense of immediate energy intake, suggesting that between-group competition is a key driver of fine-scale home range use in sakis.

A Saki Saga: Dynamic and Disruptive Relationships among Pithecia aequatorialis in Ecuador.

Saki monkeys live in socially monogamous groups and in groups containing more than one same-sex adult. As part of a 10-year study of equatorial sakis (Pithecia aequatorialis) in Ecuador, we documented the immigration of a second adult male into a group containing a resident male-female pair that had associated with one another for seven years and the resident female's two daughters. In the first month after immigration, the resident male spent more time closer to and grooming his putative adult daughter than the resident female, and the two males were seen performing a cooperative territorial display. After two months, the resident male interacted more with the resident female than with his putative adult daughter, while that daughter interacted more with the immigrant male and copulated with him. After three months, the males left the group together and associated with an unfamiliar female, leaving the resident females and a neonate behind. The resident male then paired with a new female, while the immigrant male joined another group, again as a second male. Compared to other socially monogamous primates, sakis appear to have a more variable social system whereby additional males can join established groups and form relationships with putatively unrelated males.

Spatial foraging in free ranging bearded sakis: traveling salesmen or Lévy Walkers?

According to optimal foraging theory and most current models of primate socioecology, primate foraging involves a series of decisions concerning when is the most optimal time to leave a food patch, how to travel to the next patch in an efficient manner, and how to minimize the time and distance traveled to all patches throughout the course of the day. In this study, I assess how bearded sakis solve these challenges by presenting data on their patch use, distance minimization, and by comparing their movements with non-deterministic foraging patterns. The study group, composed of 38 ± 15 individuals, fed significantly longer in higher quality patches (quality defined by patch size and productivity) and in those that contained ripe fruit pulp. However, group size was not a significant predictor of patch occupancy. Bearded sakis traveled relatively directly between food patches, sometimes over distances > 300 m. In addition, they chose the optimal daily path among all patches visited on 9 of 17 occasions, and on average traveled only 21% more than the least distance route. Bearded saki step lengths were consistent with a Brownian rather than a Lévy Walk pattern while waiting times were consistent with a Lévy pattern. However, the distribution of their turning angles indicated a high degree of directional persistence between patches. These results suggest that bearded sakis exploit food patches that are randomly distributed spatially but heterogenous in patch quality. They appear to encode the locations of high quality food patches and minimize travel between them, despite opportunistically feeding from more abundant and randomly distributed, lower quality patches en route.

Sleeping site selection by golden-backed uacaris, Cacajao melanocephalus ouakary (Pitheciidae), in Amazonian flooded forests.

In Amazonian seasonally flooded forest (igapó), golden-backed uacaris, Cacajao melanocephalus ouakary, show high selectivity for sleeping trees. Of 89 tree species in igapó, only 16 were used for sleeping (18%). Hydrochorea marginata (Fabaceae) and Ormosia paraensis (Fabaceae) were used most frequently (41% of records) despite being uncommon (Ivlev electivity ratios were 0.76, and 0.84, respectively), though the third most commonly used species (11%), Amanoa oblongifolia (Euphorbiaceae), was selected at near parity. All three species have broad, open canopies with large horizontal limbs and uncluttered interiors. Compared with random trees, sleeping trees had above average diameter at breast height (DBH) and height, lacked lianas and wasp nests, and were more frequently within 5 m of open water. Uacaris generally slept one adult per tree or widely separated in the same canopy and on the outer third of the branch. These behaviours are interpreted as maximising detection of both aerial and arboreal predators.

Seasonal versatility in the feeding ecology of a group of titis (Callicebus coimbrai) in the northern Brazilian Atlantic Forest.

The feeding behavior of a group of titis (Callicebus coimbrai) was monitored over an annual cycle at a site in northeastern Brazil. Behavioral data were collected in scan samples (1-min scan at 5-min intervals), and complementary data on fruit availability and new leaf cover were collected. Feeding time accounted for 28.9% of daily activity. Fruit was the principal item of the diet (61.2% of records) and the primary category in all months except September, when it was surpassed by leaves. Young leaves were the second most important category (20.0%). The consumption of seeds and insects was prominent in November and December. Fifty-two plant species were exploited, and the Elaeocarpaceae, Myrtaceae, Sapotaceae, and Passifloraceae provided the vast majority (86.0%) of plant feeding records. The phenological record did not provide a good measure of fruit availability, but a strong correlation (r(s) =0.902, P<0.0001, n=12) was found between the consumption of leaves and the exploitation of lianas each month. Lianas accounted for 28.2% of plant feeding records, and predominated between August and December. This suggests that lianas may represent a key factor in the ability of the species to tolerate the intense habitat fragmentation found throughout its geographic range.

Use of sleeping sites by a titi group (Callicebus coimbrai) in the Brazilian Atlantic Forest.

Predation pressure affects most aspects of primate behaviour, and is especially pronounced in the context of the use of sleeping sites, given the vulnerability of the animal at this time. Most small-bodied platyrrhines have highly systematic patterns of sleeping site choice and use. This study analyses the use of sleeping sites by a free-ranging group of titis (Callicebus coimbrai) monitored at a site in Sergipe, Brazil, between July, 2009 and June, 2010. When the subjects approached a sleeping tree their behaviour was typically cautious, including slow and silent movement, early retirement (20-162 min before sunset on 52 dry afternoons), and sleeping in a tight huddle with their tails entwined. Despite this behaviour, which has an obvious anti-predator function, the group slept in only three different trees during the course of the study, and returned to the same tree used on the previous night on a quarter of evenings (n = 56). This was despite the availability within the group's home range of a large number of trees with similar structural characteristics (i.e. tall, open crown in the upper canopy). Surprisingly, the three trees were all members of the same species, Licania littoralis (Chrysobalanaceae). The choice of this species, which was not an important source of dietary resources, and the repeated use of a small number of sites, did not seem to be related to factors such as ranging or foraging patterns, but may have a been a response to the specific threat from capuchins, Cebus xanthosternos.

Predation and predation attempts on red titi monkeys (Callicebus discolor) and equatorial sakis (Pithecia aequatorialis) in Amazonian Ecuador.

Anecdotal reports of predation as well as observed predation attempts and rates of animal disappearance provide some of the most relevant data for evaluating the influence that predation risk may have on primate behavioural ecology. Here, we report rates of disappearance from six groups of red titi monkeys (Callicebus discolor) and two groups of equatorial sakis (Pithecia aequatorialis) followed over a period of four and a half years at a lowland site in Amazonian Ecuador. We also describe the first direct observation of a harpy eagle (Harpia harpyja) preying upon a titi monkey, as well as 3 unsuccessful attacks by tayras (Eira barbara) on titi monkeys and 4 unsuccessful attacks by various raptors on sakis. Our data indicate that pitheciid primates may face a wider array of possible predators than previously recognized, and that titi monkeys and sakis are susceptible to different major classes of predators. Our observations also suggest differences in the sex role during predator defence that could be related to the evolution and maintenance of monogamous systems.

Observed case of maternal infanticide in a wild group of black-fronted titi monkeys (Callicebus nigrifrons).

A maternal infanticide was observed in a group of unprovisioned wild black-fronted titi monkeys (Callicebus nigrifrons). An approximately 3-day-old male infant was killed by his mother. A post-mortem revealed the infant to be clinically healthy. We considered various hypotheses to explain why this behavior occurred (e.g., reproductive advantage, stress, nutritional, infant viability and population density). It is noteworthy that the mother and not the father killed the infant, since in this species the father provides considerable infant care from a few hours after birth.