Amy L. Schreier

The fourth level of social structure in a multi‐level society: ecological and social functions of clans in hamadryas baboons

Hamadryas baboons are known for their complex, multi‐level social structure consisting of troops, bands, and one‐male units (OMUs) [Kummer, 1968. Social organization of hamadryas baboons. Chicago: The University of Chicago Press. 189p]. Abegglen [1984. On socialization in hamadryas baboons: a field study. Lewisburg, PA: Bucknell University Press. 207p.] observed a fourth level of social structure comprising several OMUs that rested near one another on sleeping cliffs, traveled most closely together during daily foraging, and sometimes traveled as subgroups independently from the rest of the band. Abegglen called these associations “clans” and suggested that they consisted of related males. Here we confirm the existence of clans in a second wild hamadryas population, a band of about 200 baboons at the Filoha site in lowland Ethiopia. During all‐day follows from December 1997 through September 1998 and March 2005 through February 2006, data were collected on activity patterns, social interactions, nearest neighbors, band fissions, and takeovers. Association indices were computed for each dyad of leader males, and results of cluster analyses indicated that in each of the two observation periods this band comprised two large clans ranging in size from 7 to 13 OMUs. All band fissions occurred along clan lines, and most takeovers involved the transfer of females within the same clan. Our results support the notion that clans provide an additional level of flexibility to deal with the sparse distribution of resources in hamadryas habitats. The large clan sizes at Filoha may simply be the largest size that the band can split into and still obtain enough food during periods of food scarcity. Our results also suggest that both male and female relationships play a role in the social cohesion of clans and that males exchange females within clans but not between them. Am. J. Primatol. 71:948–955, 2009.

Female “dispersal” in hamadryas baboons: Transfer among social units in a multilevel society

Unlike most cercopithecines, hamadryas baboons (Papio hamadryas hamadryas) are characterized by female-biased dispersal. To clarify this pattern within the context of their hierarchical social system (comprising one-male units, clans, bands, and troops), we report here 7 years of data on female transfers among social units in wild hamadryas baboons in Ethiopia. Female tenure in one-male units (OMUs) ranged from 1 to 2,556 days (N = 208) and survival analysis revealed a median tenure length of 1,217 days (40 months). Changes in OMU membership consisted almost exclusively of takeovers by males, not voluntary transfer. Of 130 takeovers, 67% occurred within the band and 33% across bands, and, of the 22 takeovers for which we have clan membership data, 77% occurred within, not between, clans. These results reinforce the notion that hamadryas female dispersal is not analogous to sex-biased dispersal in other taxa, because (1) at least in Ethiopian populations, females do not disperse voluntarily but are transferred, often forcibly, by males; (2) only dispersal between bands will promote gene flow, whereas females are most often rearranged within bands; (3) hamadryas females undergo social dispersal but not usually locational dispersal; and (4) while male hamadryas are far more philopatric than females, they have been observed to disperse. It thus appears that the ancestral baboon pattern of female philopatry and male dispersal has evolved into a system in which neither sex is motivated to disperse, but females are forcibly transferred by males, leading to female-mediated gene flow, and males more rarely disperse to find females.

Composition and seasonality of diet in wild Hamadryas baboons: preliminary findings from Filoha.

Here we report the first year-round quantitative data on dietary composition and seasonality in wild hamadryas baboons. Study subjects were adult male members of band 3 at the Filoha field site in central lowland Ethiopia. Data collection consisted of 10-min focal samples during all-day follows 4–6 days per month over the course of 1 year. The two largest contributors to the diet were Hyphaene thebaica and Acacia senegal, and these were the only plant species found in the diet during every month of the year. Other relatively major contributors to the diet, such as Cyperus grandibulbosus, Seddera bagshawei, Tribulus cistoides and Typhalatifolia, showed a seasonal pattern. Fewer plant species were consumed during the dry months of the year compared to the wet months. During the hottest and driest months of the year, study subjects subsisted almost exclusively on H. thebaica, A. senegal, C. grandibulbosus and T.latifolia. Overall, these patterns suggest that this population of hamadryas baboons spends less time feeding and is able to subsist on a narrower array of plant foods compared to other baboons. This pattern may be driven by the presence at Filoha of the doum palm (H. thebaica), a high-quality food resource that is consumed year-round.

Ecology and Sociality in a Multilevel Society: Ecological Determinants of Spatial Cohesion in Hamadryas Baboons

The multilevel society of hamadryas baboons, consisting of troops, bands, clans, and one-male units (OMUs), is commonly perceived to be an effective means of adapting to variable food availability while allowing spatial cohesion in response to predator pressure. The relationship between these variables, however, has never been tested quantitatively. The Filoha site in Awash National Park, Ethiopia is ideally suited to such an investigation as it contains nutrient-dense palm forests in addition to the Acacia scrublands typical of hamadryas distribution elsewhere, allowing comparisons of spatial cohesion across habitat types. Here, we use observations over a 1-year period to examine the relationship between resource availability, perceived predator pressure, and spatial cohesion in a band of wild hamadryas baboons at Filoha. Our results demonstrate that the band was more likely to break into OMUs when foraging in habitats with lower food availability, and that the band fissioned into independent clans more often when preferred resources were not available. Furthermore, the baboons remained in larger aggregations for longer periods of time (i.e., prior to embarking on their daily foraging route) on mornings after predators were heard in the vicinity, and increased cohesion in response to encounters with people who may have been perceived as predators. These results support the notion that hamadryas baboons change their social groupings in response to both food availability and predation risk and that the ability of hamadryas bands to cleave and coalesce in response to changes in these factors underlies the evolution of the hamadryas modular social structure.

The Socioecology of Network Scaling Ratios in the Multilevel Society of Hamadryas Baboons (Papio hamadryas hamadryas)

Multilevel or modular societies characterize a range of mammalian taxa, allowing social groups to fission and fuse in response to ecological factors. The modular society of hamadryas baboons has previously been shown to consist of 4 levels: troop, band, clan, and one-male unit (OMU). A recent study by Hill et al. (Biology Letters 4:748–751, 2008) revealed a mean scaling ratio across successive levels of multilevel societies of ca. 3; this was consistent across elephants, orca, geladas, and hamadryas baboons. Here we reanalyze the scaling ratio for hamadryas baboons with previously unavailable data from Filoha. Our analysis revealed a mean scaling ratio for hamadryas of 3.28 without data on the hamadryas clan layer of organization at Filoha, but a ratio of 6.17 with these data included. This discrepancy is due to the large clan and band sizes at Filoha yielding a larger than average gap between the OMU and the clan. Further analysis revealed subsets of OMUs within clans, suggesting a 5th level of society in this population. When this 5th layer of social structure is included in the analysis, the scaling ratio at Filoha is consistent with that of other hamadryas populations and other taxa. These results suggest that a consistent mammalian scaling ratio can be used to detect previously hidden levels of organization within societies and to predict their sizes in taxa for which detailed behavioral data are not available.

Feeding ecology, food availability and ranging patterns of wild hamadryas baboons at Filoha.

Most hamadryas baboons rely on Acacia species for subsistence in their semidesert habitats. Unlike other hamadryas sites, palm forests at Filoha in Awash National Park, Ethiopia, provide the baboons with a preferred food resource close to a commonly used sleeping site. The baboons are expected to feed on doum palm trees when fruit is available, and this resource use should play a role in ranging patterns. This paper describes the feeding ecology, food availability and ranging patterns of a band of wild hamadryas baboons at Filoha from March 2005 to February 2006. Data on feeding and ranging behavior derive from band scans during all-day follows of baboons, and data on food availability derive from monthly phenological monitoring of frequently consumed food species. The baboons fed predominantly on palms when fruit was available, and preferred the flowers of Acacia senegal to its leaves. There was no relationship between daily path length and the proportion of palm fruit in the baboons’ diet, but changes in the availability of fruit across the Filoha region appear to mirror the baboons’ shifting use of its home range. The large band sizes at Filoha may obscure the effects doum palm fruit might have on ranging patterns.

Recurrent patterning in the daily foraging routes of hamadryas baboons (Papio hamadryas): Spatial memory in large-scale versus small-scale space

The benefits of spatial memory for foraging animals can be assessed on two distinct spatial scales: small‐scale space (travel within patches) and large‐scale space (travel between patches). While the patches themselves may be distributed at low density, within patches resources are likely densely distributed. We propose, therefore, that spatial memory for recalling the particular locations of previously visited feeding sites will be more advantageous during between‐patch movement, where it may reduce the distances traveled by animals that possess this ability compared to those that must rely on random search. We address this hypothesis by employing descriptive statistics and spectral analyses to characterize the daily foraging routes of a band of wild hamadryas baboons in Filoha, Ethiopia. The baboons slept on two main cliffs—the Filoha cliff and the Wasaro cliff—and daily travel began and ended on a cliff; thus four daily travel routes exist: Filoha–Filoha, Filoha–Wasaro, Wasaro–Wasaro, Wasaro–Filoha. We use newly developed partial sum methods and distribution‐fitting analyses to distinguish periods of area‐restricted search from more extensive movements. The results indicate a single peak in travel activity in the Filoha–Filoha and Wasaro–Filoha routes, three peaks of travel activity in the Filoha–Wasaro routes, and two peaks in the Wasaro–Wasaro routes; and are consistent with on‐the‐ground observations of foraging and ranging behavior of the baboons. In each of the four daily travel routes the “tipping points” identified by the partial sum analyses indicate transitions between travel in small‐ versus large‐scale space. The correspondence between the quantitative analyses and the field observations suggest great utility for using these types of analyses to examine primate travel patterns and especially in distinguishing between movement in small versus large‐scale space. Only the distribution‐fitting analyses are inconsistent with the field observations, which may be due to the scale at which these analyses were conducted. Am. J. Primatol. 76:421–435, 2014.

Testing parallel laser image scaling for remotely measuring body dimensions on mantled howling monkeys (Alouatta palliata)

Body size is a fundamental variable for many studies in primate biology. However, obtaining body dimensions of wild primates through live capture is difficult and costly, so developing an alternative inexpensive and non‐invasive method is crucial. Parallel laser image scaling for remotely measuring body size has been used with some success in marine and terrestrial animals, but only one arboreal primate. We further tested the efficacy of this method on the arboreal mantled howling monkey (Alouatta palliata) in La Pacifica, Costa Rica. We calculated interobserver error, as well as the methods repeatability when measuring the same animal on different occasions. We also compared measurements obtained physically through live capture with measurements obtained remotely using parallel laser image scaling. Our results show that the different types of error for the remote technique are minimal and comparable with the error rates observed in physical methods, with the exception of some dimensions that vary depending on the animals’ posture. We conclude that parallel laser image scaling can be used to remotely obtain body dimensions if careful consideration is given to factors such as species‐specific morphology and postural habits. Am. J. Primatol. 77:823–832, 2015.

The influence of anthropogenic edge effects on primate populations and their habitat in a fragmented rainforest in Costa Rica

When a forest is fragmented, this increases the amount of forest edge relative to the interior. Edge effects can lead to loss of animal and plant species and decreased plant biomass near forest edges. We examined the influence of an anthropogenic forest edge comprising cattle pasture, coconut plantations, and human settlement on the mantled howler (Alouatta palliata), white-faced capuchin (Cebus capucinus), Central American spider monkey (Ateles geoffroyi), and plant populations at La Suerte Biological Research Station (LSBRS), Costa Rica. We predicted that there would be lower monkey encounter rate, mean tree species richness, and diameter at breast height (DBH) in forest edge versus interior, and that monkeys would show species-specific responses to edge based on diet, body size, and canopy height preferences. Specifically, we predicted that howler monkeys would show positive or neutral edge effects due to their flexible folivorous diet, large body size, and preference for high canopy, capuchins would show positive edge effects due to their diverse diet, small body size, and preference for low to middle canopy, and spider monkeys would show negative edge effects due their reliance on ripe fruit, large body size, and preference for high upper canopy. We conducted population and vegetation surveys along edge and interior transects at LSBRS. Contrary to predictions, total monkey encounter rate did not vary between the forest edge and forest interior. Furthermore, all three species showed neutral edge effects with no significant differences in encounter rate between forest edge and interior. Interior transects had significantly higher mean tree species richness than edge transects, and interior trees had greater DBH than edge trees, although this difference was not significant. These results suggest that forest edges negatively impact plant populations at La Suerte but that the monkeys are able to withstand these differences in vegetation.