Activity patterns and feeding behaviour of the tree hyrax, Dendrohyrax arboreus, in the Parc National des Volcans, Rwanda

Activity patterns of Dendrohyrax arboreus were investigated by direct observation of a habituated population in the Parc National des Volcans, Rwanda. Of seventeen animals caught, four were males and thirteen were females. Of the population, 17% were juveniles. Population estimates from transects indicated a biomass of 23.3 kg/ha. Radio-tracking of ten individuals showed bimodal activity patterns, with peaks after dusk and later in the night for males and during the day in females. Hyrax were active 16% of the time. Feeding was the dominant activity and mature leaves of Hagenia abyssinica were the most important food. Travelling within and between trees occupied 4% of the time and occurred predominantly during daylight hours. Calling behaviour was markedly seasonal, being most pronounced in the dry season when hyrax called regularly in the early evening, and often a second time late at night. During the rains, calls were infrequent and unpredictable, tending to occur in the second half of the night. There was no correlation between weather or lunar conditions and calling behaviour. The ecological strategy of tree hyrax in terms of metabolic rate, thermoregulation and energy conservation is discussed in the light of their activity and feeding behaviour.     

Hand preference in unimanual and bimanual tasks and postural effect on manual laterality in captive red-capped mangabeys (Cercocebus torquatus torquatus)

Hand preference in 11 captive red-capped mangabeys (Cercocebus torquatus torquatus) was examined under different conditions: a free situation during spontaneous food processing, three different postural conditions (brachiating, and bipedal and tripedal standing), and a situation involving bimanual processing. Generally, individual laterality was found regardless of the task and behavior involved. However, the number of monkeys with hand preferences and the strength of the preference increased with the complexity of the tasks. The monkeys exhibited a significantly higher and positive mean manual preference index (HI) when they were hanging than when they were quadrupedal or sitting. The strength of manual preference (ABS-HI) was in turn higher when the monkeys were hanging or bipedal than when they were quadrupedal. The strength of manual preference was higher for both the bimanual and experimental tasks than for unimanual tasks and spontaneous activities. Although our sample was too small to allow us to make any generalizations concerning lateral preferences in red-capped mangabeys, we propose some hypotheses about the influence of posture stability and task complexity.     

Thermoregulatory behaviour in Tropidurus torquatus (Squamata, Tropiduridae) from Brazilian coastal populations: an estimate of passive and active thermoregulation in lizards

Geographical variation in the degree of thermoregulatory behaviour of the lizard Tropidurus torquatus was studied in 10 restinga populations along approximately 1500 km of Brazilian coast. An index of thermoregulation was estimated using the difference between body and environmental (air and substrate) temperatures and the percentage of negative values for these differences (proportion of body temperatures lower than environmental temperatures). In most populations, the lizards primarily used active thermoregulation, through behavioural means, and mainly in relation to substrate temperatures. Along the restingas, the degree of active thermoregulation increased as a function of the increase in the local environmental temperatures along the restingas. Behavioural thermoregulation of T. torquatus helps the lizards to maintain their body temperatures within an optimal range in which to perform their normal daily activities.     

Intergroup loud calls,range size,and spacing in Callicebus torquatus

Observations are reported on the response of a free-ranging group of Callicebus torquatus to recordings of loud intergroup calls. When the recording consisted of the call of a solo adult male, the group fled from the recording. When the recording consisted of the adult male and female duetting together, the group remained in place and called back to the recording. These results contrast with previously described vocal and spatial responses of C. moloch and suggest that range size influences the mechanisms that regulate between-group spacing. The consequence of intergroup loud calls in C. moloch is to define and reinforce the location of boundaries, whereas in C. torquatus, homologous calls maintain spacing between groups.     

The socioecology of the black mangabey (Cercocebus aterrimus) near Lake Tumba,Zaire

Socioecological data were gathered in a two-year study of black mangabey monkeys in a secondary forest on the west bank of Lake Tumba, Zaire. The mangabeys of the study area lived in multi-male, multi-female groups numbering between 14 and 19 individuals. They were completely arboreal, fed mostly on fruit and nuts, and frequently were associated with other species of arboreal monkeys. Their predators were human hunters and the crowned hawk-eagle. The primary vocalizations of black mangabeys were analyzed and their social contexts compared with those of closely related gray-cheeked mangabeys, to which they were found to be very similar.     

Feeding ecology and postural behaviour of the three-toed sloth (Bradypus variegatus flaccidus) in northern Venezuela

We studied the diet, activity budget, vertical ranging, and postural behaviour in relation to weather of the three-toed sloth (Bradypus variegatus flaccidus) in disturbed montane forest remnants (1150 m asl) in northern Venezuela. Sloths spent most (72.9%) of their time resting and had a nearly exclusive (99.4%) leaf diet. While resting they assumed a sitting – not hanging – posture mostly (90.2% of observations). Species of three families, Clethraceae, Cecropiaceae, and Clusiaceae accounted for 77% of feeding records. Young leaves (67.2%) accounted for most of the leaf diet. Activity and posture were dependent on weather conditions. Sloths fed more often during mid-day hours and tended to rest more at dawn and dusk. In northern Venezuela sloths tended to use more frequently the upper strata of the canopy, while in warmer lowland sites they use intermediate levels more often. They adopted postures that maximized exposure of ventral surfaces to incident solar radiation when sunny, but minimized their surface area by huddling when cloudy, foggy or rainy. We propose that sunning behaviour of sloths may speed up their fermentation rate, and ultimately, might have been an important selective factor in the evolution of derived upside-down posture of sloths.     

DYNAMIC RESPONSE ANALYSIS. II.EVALUATION OF DYNAMIC RESPONSE ANALYSIS IN A SIMULATED NO-HARVEST CASE

A new method of stock assessment, dynamic response analysis, allows a qualitative assessment of stock status relative to its level of maximum net productivity to be carried out with minimal data. This paper evaluates the performance of dynamic response analysis on a simulated population under variable conditions with uncertain data. In the no-harvest case the data consist simply of a temporal sequence of relative population sizes. Dynamic response analysis is most sensitive to the number and precision of the population estimates and least sensitive to environmental variability and the intrinsic population growth rate. Significance levels must be chosen carefully, since some combinations of parameters and error levels result in an unacceptably low proportion of correct assessments. Dynamic response analysis can be a useful stock assessment technique for the management of marine mammals, but attention must be paid to the quantity and quality of the data.