Female-Female Competition in Bornean Orangutans

The mostly solitary ranging of orangutans and the large areas over which they traverse have hampered quantification of Bornean orangutan ranging patterns and feeding competition. Because of their semisolitary existence, female orangutans have few competitive interactions among themselves. However, contest and scramble types of competition occur, and researchers consider both to be important for the species. Using 9 yr of data and >22,300 h of observation of adult female orangutans in Gunung Palung National Park in Indonesian Borneo, we examined both forms of competition. Based on our analyses, we have 4 conclusions: 1) Adult female orangutans have highly overlapping home ranges, and thus there is potential for scramble competition to impose a cost. 2) Adult female orangutans actively avoid each other, suggesting that scramble competition indeed imposes a cost. 3) Adult females have distinct core areas that overlap to a lesser degree than home ranges do. 4) Analyses of contest competition reveal a slight spatial component to female competition for the first time. Preliminary evidence for core area defense and passive range exclusion may be among the mechanisms responsible for maintaining distinct adult female core areas.     

Ranging Behavior of Two Species of Guenons (Cercopithecus lhoesti and C. mitis doggetti) in the Nyungwe Forest Reserve,Rwanda

I studied the ranging behavior of one group of L'Hoest's monkeys (Cercopithecus lhoesti) and one group of blue monkeys (C. mitis doggetti) in the Nyungwe Forest Reserve, Rwanda. This study is the first to examine the ranging behavior of the more terrestrial L'Hoest's monkeys. Fruits composed 47% of blue monkey diet and 24% of the L'Hoest's monkey diet; terrestrial herbaceous vegetation composed 35% of the diet of the latter. While overall abundance of fruit resources in the home range and overall proportion of fruit in the diet were not related to ranging behavior in either group, temporal and spatial availability of specific fruit species was related. Measures of ranging behavior indicated a more concentrated ranging pattern when fruit resources were scarce and dietary diversity increased and when fruit resources were abundant and the groups focused on a few abundant fruit species. Current hypotheses concerning primate ranging behavior suggest that frugivorous species are expected to have greater day ranges and larger home ranges than folivorous species, and invertebrate consumption is expected to produce a more wide-ranging pattern. However, the L'Hoest's monkey group, which was more folivorous and consumed fewer invertebrates, traveled greater daily distances, had a more diverse and longer ranging pattern, and had larger home range areas than the blue monkey group in every month of the study. Both species were highly selective of forest habitats; L'Hoest's monkeys used secondary forest, while blue monkeys preferred primary forest.     

Ranging Behavior of Proboscis Monkeys (Nasalis larvatus) in the Lower Kinabatangan, Northern Borneo

I studied the ranging behavior of proboscis monkeys (Nasalis larvatus) at two sites in the Lower Kinabatangan Region of northern Borneo. I collected data on ranging behavior via scan sampling during group follows. Groups of Nasalis larvatus had ranges overlapping those of other groups in each area. I observed no territorial behavior. Groups of Nasalis larvatus occasionally swam across the Kinabatangan River, and frequently across its tributaries. The home range size of a focal one-male group (SU1) was 220.5 ha. The group traveled farther on days when the proportion of young leaves in the diet was higher. In addition, SU1 used particular areas when they fed on flowers and fruits. Apparently, rainfall and phenology did not influence ranging patterns.     

Effects of Seasonal Water Scarcity on the Ranging Behavior of Eulemur fulvus rufus

The climate of western Madagascar is characterized by a long (8–9 mo) dry season during which small rivers run dry, so that most animals are dependent on access to a few permanent water holes. We studied the effects of water scarcity at the end of the dry season on the ranging behavior of 4 groups of redfronted lemurs (Eulemur fulvus rufus) living at different distances from the Kirindy Riverbed in the Kirindy/CFPF forest northeast of Morondava. Using radio-collars, we located 2 resident groups with permanent home ranges near the river, and 2 non-resident groups and followed them for 60 days. We obtained a GPS reading every 30 min and later analyzed them with GIS ArcView to determine the size and location of each group's (core) home range. One group resided in direct proximity to the riverbed with several water holes and made regular short trips (mean 330 m) to drink. A second resident group had no direct access to water and made regular trips to the same water hole at a mean distance of 590 m from their home range. One non-resident group had a center of activity about 1300 m from the nearest water hole, to which they traveled on a non-daily basis. The other non-resident group established a temporary binuclear home range with one center of activity near the riverbed, about 2900 m away from the other center of activity. Thus, redfronted lemurs use different drinking and ranging tactics as a function of the distance of their core areas from the nearest water source.     

Diet and Travel Costs for Spider Monkeys in a Nonseasonal, Hyperdiverse Environment

I studied the effects of a nonseasonal environment with a high diversity of plant species in a community of white-bellied spider monkeys (Ateles belzebuth belzebuth) in the Yasuní National Park, Ecuador. During 10 2-wk follows of focal individuals across 1 yr, I collected 1268 h of observation data on ranging and foraging. The environment had strong effects on both the foraging and ranging behavior of the monkeys. Yasuní spider monkeys are similar to spider monkeys in more seasonal environments in that ripe-fruit consumption dominates the diet. However, Yasuní spider monkeys exhibit an extremely diverse diet that parallels the variety of foods available to them, consuming more than 238 species of fruits. The impressive dietary variety increased even more with increased observation time, as I had not previously observed in the spider monkeys’ diet 40% of the fruit species the subjects consumed during the final follow. Ripe fruits remain the most important item in the diet year-round, supplemented with decayed wood or leaf flush. Local rarity of plant species means that fruiting patches are an average of 420 m apart, and mean patch residence times are short, only 8.1 min. Visits to an average of 11.5 feeding patches/d lead to a mean daily path length of 3311 m, longer than reported for any other Ateles species, and long compared to most other primate species. The long daily paths of Yasuní spider monkeys reflect travel costs resulting from foraging in a hyperdiverse nonseasonal environment.     

Preliminary observations on the role of Acacia gum chemistry in Acacia utilization by Galago senegalensis in Kenya

A census and preliminary observations on the ranging and feeding behavior of Galago senegalensis were made in a savannah-woodland site in Kenya. Population densities in three slightly different habitats were all approximately 1.5 animals/ha. Ranging patterns suggested the existence of territorial behavior. The diet of the galagos was exclusively insects and gums of two species of Acacia. The gum of A. drepanolobium appeared to be preferred to that of A. xanthophloea. The chemistry of the gums suggests that this preference is not due simply to the total level of phenolics or to avoidance of condensed tannins but may relate to the presence of compounds (e. g., flavonoids) having nutritional or hormonelike action.     

Female Competition over Core Areas in <Emphasis Type="Italic">Pan troglodytes schweinfurthii</Emphasis>, Kibale National Park,Uganda

Aggression is rare among wild female chimpanzees. However, in the Kanyawara chimpanzee community in Kibale National Park, Uganda, stable use of food-rich core areas is linked to increased reproductive success, suggesting that contest competition might occur over access to the highest-quality ranges. To examine this hypothesis, we studied aggression and dominance relationships among Kanyawara females during a 10-yr period that included the immigration of 5 females into the community. We tested 2 predictions: 1) that female-female aggression should intensify when immigrants enter the community because this is when core area access is determined and 2) that the quality of core areas should reflect relative female dominance relationships. In support of the first prediction, female-female aggression increased 4-fold when new immigrants were in the community, with rates peaking when there were multiple immigrants. This pattern was due primarily to aggression by resident mothers toward immigrants and featured coalitionary aggression, a rare behavior among female chimpanzees. In support of the second prediction, females occupying core areas high in foraging quality ranked high overall and higher than expected for their ages, whereas females occupying low-quality core areas were lower-ranking and ranked lower than expected for their ages. Together, the data indicate that though female aggression does not regularly occur in chimpanzees, contest competition continues to play an important role in determining long-term access to resources, an important correlate of reproductive success.