Relationships among brown lemurs (Eulemur fulvus) based on mitochondrial DNA sequences

The brown lemurs (Eulemur fulvus) include seven subspecies, whose evolutionary relationships remain contentious. In particular, it is unclear whether the Malagasy and Comorian E. f. fulvus populations are differentiated at the subspecific level (E. f. mayottensis). Furthermore, it has been suggested that E. f. collaris and E. f. albocollaris are separate species. Analyses of approximately 2400 bp of mitochondrial DNA sequence data from part of the COIII gene, together with complete genes for ND3, ND4L, and ND4 and 5 tRNAs, resolved 34 E. fulvus specimens into six clades: ((albocollaris, collaris) (rufus (rufus (fulvus/mayottensis (albifrons/fulvus/sanfordi))))). Based on the information available and our analyses we conclude that E. f. albocollaris and E. f. collaris do not represent species distinct from E. fulvus and that Comorian brown lemurs do not deserve subspecific rank. No genetic differentiation was detected between E. f. albifrons and E. f. sanfordi; on the other hand, there are obviously two separate lineages of E. f. rufus.     

Edge effects and their influence on lemur density and distribution in Southeast Madagascar

Edge effects are caused by the penetration of abiotic and biotic conditions from the matrix into forest interiors. Although edge effects influence the biogeography of many tropical organisms, they have not been studied directly in primates. Edge effects are particularly relevant to lemurs due to the loss of 80-90% of forests in Madagascar. In this study, data are presented on how biotic edge effects influenced the distribution and density of lemurs in the Vohibola III Classified Forest in southeastern Madagascar. In total, 415 lemur surveys were conducted during June-October 2003 and May-September 2004 along six 1,250-m transects that ran perpendicular to the forest edge. Data were also collected on lemur food trees along the six transects (density, height, diameter at breast height, area, volume, and distance to forest edge). Four nocturnal species (Avahi laniger, Cheirogaleus major, Lepilemur microdon, and Microcebus rufus) and four diurnal species (Eulemur rubriventer, Eulemur fulvus rufus, Hapalemur grisesus griseus, and Propithecus diadema edwardsi) were sighted during surveys. Regression analyses of lemur densities as a function of distance to forest edge provided edge tolerances for A. laniger (edge-tolerant), M. rufus (edge-tolerant), E. rubriventer (edge-tolerant or omnipresent), and H. g. griseus (omnipresent). The density and distribution of M. rufus and their foods trees were correlated. Edge-related variations in food quality and predation pressures may also be influencing lemurs in Vohibola III. Tolerance for edge effects may explain, in part, how lemurs have survived extreme habitat loss and forest fragmentation in southeastern Madagascar.     

Adult Male Scent-Marking in Lemur catta and Eulemur fulvus rufus

Scent-marking and olfactory communication are used extensively by prosimians and can provide spatial and temporal records of group movement and behavior. We compare rates of male scent-marking in relation to reproductive seasons, male dominance rank, and habitat use in two related prosimians: Lemur catta and Eulemur fulvus rufus. We collected scent-marking data on adult male Lemur catta at Beza-Mahafaly Reserve (dry forest), and on Eulemur fulvus rufus at Ranomafana National Park (rainforest), Madagascar. In Lemur, rates of overall scent-marking differed significantly by reproductive season, with higher rates occurring in mating and lactation/migration periods, whereas in Eulemur, reproductive season did not appear to affect scent-marking rates. Dominance rank of male Lemur catta did not affect rates of scent-marking. Among male Eulemur fulvus, dominance relations were not apparent; however, 2 of the 5 focal males scent-marked somewhat more frequently during the mating season and also experienced greater mating success. In Lemur catta, higher rates of scent-marking in the mating season may relate to indirect reproductive competition during a period of high aggression, while such mating competition was not as marked in Eulemur fulvus. Furthermore, higher rates of marking in resident male Lemur catta during male migration may correlate with vigilance toward immigrating males. Greater overall scent-marking rates in ring-tailed lemurs may relate to extensive intergroup home range overlap and no area of exclusive use, whereas the red-fronted lemur groups tended to forage in areas of their home range where little-to-no intergroup overlap occurred.     

Habitat shifting by the common brown lemur (Eulemur fulvus fulvus): a response to food scarcity

During periods of food scarcity, most primates display behavioral responses, such as dietary switching or adjustment of traveling and foraging efforts, within home ranges. In rare cases, several primate species leave their home ranges for other remote habitats to seek alternative resources; this migration-like behavior is termed “habitat shifting.” Reports of habitat shifting have concentrated on platyrrhines, but this behavior has rarely been observed among prosimians. During 1 year of observation of a troop of common brown lemurs (Eulemur fulvus fulvus) in Ankarafantsika National Park, northwestern Madagascar, habitat shifting occurred twice. To understand the causes of this behavior, I examined the seasonal availability of fruit resources in the range continuously used by the troop during the year (defined as the annual range) and compared feeding activities and vegetation types between the annual range and new areas. The troop usually stayed within a 38.7-ha annual range, defined by a 95 % fixed kernel analysis based on GPS location data collected at 5-min intervals. In April 2007, the lemurs suddenly moved to a habitat 1.0–1.5 km south of their annual range and concentrated on the consumption of Grewia triflora fruits for 2 weeks. In November 2007, they visited a habitat 0.8–1.7 km southeast of the annual range and exploited fruits of Landolphia myrtifolia. These new areas were open habitats with high densities of the respective fruit species. The density of fruiting trees was low in the annual range during these periods; thus, habitat shifting to areas with different phenological productivity appeared to be an effective response to fruit scarcity. Brown lemurs are generally categorized as a nonterritorial species, and the lemurs observed here showed no agonistic behavior in intergroup encounters during range shifting. Such nonterritoriality may allow brown lemurs to shift habitats, a behavior resulting in long-term absence from their annual range.     

Surveys of sympatric lemurs at Anjamena, north-west Madagascar

In order to assess the status of lemurs along the lower reaches of the Mahavavy in north-west Madagascar, we carried out transect line sampling at Anjamena between April and August 1995. These data were complemented by additional absence–presence surveys conducted in 1994 and 1995 in many of the remaining forested areas of the region. This is the first study of lemur population density estimates for the faunal subregion between the rivers Mahavavy and Betisboka. Six sympatric lemurs are found at Anjamena: Cheirogaleus medius, Eulemur fulvus rufus, E. mongoz, Lepilemur sp., Microcebus murinus and Propithecus verreauxi coronatus. Data suggest that in some parts of the region large numbers of lemurs may still be found (E. f. rufus 121 individuals per km², E. mongoz (45), Lepilemur sp. (110), M. murinus (85) and P. v. coronatus (173)). No density data are provided for C. medius. In conclusion, as high lemur population densities may still be found and, in particular, P. v. coronatus is not known to exist in any protected area, Anjamena could serve as an important addition to the protected area system of north-west Madagascar.     

Brown (Eulemur fulvus) and ring-tailed lemurs (Lemur catta) use human head orientation as a cue to gaze direction in a food choice task

Whilst the ability to follow human gaze has been demonstrated in monkeys and apes, there is little evidence that prosimians share this ability. The current study used a food choice paradigm to assess whether captive brown (Eulemur fulvus) and ring-tailed lemurs (Lemur catta) use human gaze direction as a cue when choosing between an attending or non-attending human. Four experiments assessed the use of body, head and eye cues by the lemurs. In experiment 1, the non-attending human stood with her back to a food item; 3 of the 5 lemurs preferentially chose the attending human with an equivalent food item in view. In experiments 2 and 3, which used head angles of 90°, 4 out of 5 lemurs preferentially chose the attending human. In experiment 4, in which the humans differed only by whether their eyes were open or shut, no significant preferences were found. This study provides the first tentative evidence that lemurs are capable of discriminating human gaze direction and can use both body and head direction to do so.     

Habitat separation of semifree-ranging Lemur catta and Lemur fulvus

Habitat use of two semifree-ranging groups of lemurs, Lemur catta and Lemur fulvus, was studied in relation to abiotic, floristic, and structural characteristics of their enclosure. L. catta was very flexible in the use of the habitat and showed a tendency for random utilization. But this species reacted quickly to changes of the abiotic environment. L. fulvus preferred to stay in areas with dense vegetation but good lateral visibility and close to the food plants. Abiotic factors such as solar radiation and ambient temperature influenced L. fulvus to a lesser extent than L. catta. According to these results L. catta could be considered to be adapted to variable environments where it is advantageous to react quickly to changes of abiotic factors. The conservative habitat use and the limited response to abiotic factors of L. fulvus might reflect adaptations of a species living in a stable environment. If these interpretations prove correct, then this study provides another example of animals born and raised in captivity that have retained habitat preferences of their wild conspecifics.     

Census of brown lemurs (Eulemur fulvus sspp.) in southeastern Madagascar: Methods‐testing and conservation implications

Four forest areas were censused in southeastern Madagascar from June–August 1995 to estimate local population densities and habitat conditions for two threatened subspecies of brown lemur (Eulemur fulvus collaris and Eulemur fulvus albocollaris). Survey transects varied in length (1–3.5 km) and in surveillance frequency (three to seven times). Additional test surveys were conducted at the Parc National de Ranomafana to compare transect methods in an area with known population densities of Eulemur fulvus. Based on these tests, we demonstrate that the use of existing trails for transects can result in a close estimate of local population size, although more replications and longer transects increase precision. Results from regional surveys indicate considerably smaller population densities for E. f. albocollaris (0.086 animals/ha). In contrast, E. f. collaris densities were relatively high (.107 animals/ha) at Midongy‐Sud. We also noted variation among sites in the density of lianas, which was positively correlated with local population density (a possible indication of habitat degradation). More generally, habitats in E. f. albocollaris's range suffered from fragmentation, reduction in forest area, logging, and potentially greater hunting pressure. Based on these results, it is apparent that more immediate steps are necessary to preserve E. f. albocollaris populations and habitats. Am. J. Primatol. 47:51–60, 1999. © 1999 Wiley‐Liss, Inc.     

Population ecology of the ring-tailed lemur, Lemur catta, and the white sifaka, Propithecus verreauxi verreauxi, at Berenty, Madagascar, 1981

The diurnal lemurs Propithecus verreauxi verreauxi and Lemur catta at Berenty in southern Madagascar, have been studied for the last 30 years. The August 1981 census indicates that the population size of L. catta remains stable at 150 adults but that P. v. verreauxi troops have become fragmented and scattered and the population is apparently increasing. Eight different vegetation types were classified within the reserve and their influence on the distribution of L. catta and P. v. verreauxi investigated. Behavioural data obtained shows the niche separation between these two, potentially competitive, sympatric lemurs.     

Food Intake and Dietary Overlap in Native Lemur catta and Propithecus verreauxi and Introduced Eulemur fulvus at Berenty,Southern Madagascar

The introduction of Eulemur fulvus in 1975 into the Berenty Reserve and their recent attainment of population densities comparable to those of Lemur catta led us to analyze food partitioning among the 3 large prosimian species in the gallery forest. We assessed the diets of ring-tailed lemurs (Lemur catta), brown lemurs (Eulemur fulvus) and sifakas (Propithecus verreauxi) from food intake measurements during 3 successive short-term studies. All species exhibited marked seasonal changes in their major food categories. Dietary overlap was very high between ring-tailed lemurs and brown lemurs during 2 of 3 seasons, including the middle of the dry season. During the latter period, Eulemur appeared to compensate for a low quality diet by increasing the amount of food eaten. In contrast, Lemur fed on lower amounts of food and seemed more efficient at coping with fibrous plant materials. There is low dietary overlap of Lemur catta and Eulemur fulvus versus Propithecus, which exhibit by far the highest dietary diversity of the 3 species. We discuss sustainable coexistence among them, based on respective dietary adaptations and potential for dietary flexibility.     

Effect of habitat structure on positional behavior and support use in three species of lemur

This study compares locomotor and postural behavior and substrate use of three species of lemur, the diademed sifaka (Propithecus diadema edwardsi), the brown lemur (Eulemur fulvus rufus), and the red-bellied lemur (Eulemur rubriventer) at two different localities within Ranomafana National Park. The object of the study is to see if there are quantitative differences in the behavior of the lemurs or their choice of substrates in forests that have different structural attributes. Analysis of the physical characteristics of the habitat demonstrates that compared to the Talatakely area, the forest at Vatoharanana has a higher proportion of larger, taller trees. The behavior of the lemurs also differs in the two areas: all species leap less and climb and move quadrupedally more at Vatoharanana. All species use small size supports less frequently at Vatoharanana, choosing insted medium size supports (all three species) or tiny supports (Propithecus andE. fulvus) found in tree crowns and terminal branches. The lemurs prefer (i.e. use more often than would be expected based on abundance) large trees at both sites. At Vatoharanana however, they are more frequently observed higher in trees and in taller trees with greater trunk breadth. The differences in locomotor behavior are in part due to the fact that at Vatoharanana, more bouts are collected during feeding and foraging than during travel. The relationship between this difference in activity pattern and the structural differerences in the two forests, however, is not clear. This study points out the need for longer term field studies of positional behavior and substrate use that incorporate the variety of forest types the subject species inhabit.     

Ecological correlates to activity and habitat use of two prosimian primates: Eulemur rubriventer and Eulemur fulvus rufus in Madagascar

In this paper, I provide data on the possible effects of group size and seasonal changes in food availability on the activity and habitat use patterns of two species of prosimian primate: the rufous lemur (Eulemur fulvus rufus) and the red-bellied lemur (Eulemur rubriventer). General and subtle seasonal differences were observed between lemur species in (1) group size and composition, (2) activity profiles, and (3) habitat use. Rufous lemur groups were larger (mean = 8 individuals) and contained more adults than red-bellied lemur groups (mean = 3 individuals). The overall degree and distribution of diurnal activity differed between lemur species and varied within species with seasonal changes in food availability. In general, rufous lemurs traveled more often than red-bellied lemurs. During food scarcity, both species increased the amount of time spent feeding, although peak feeding and traveling times differed. Both species also preferred horizontal substrates; however, during food scarcity, red-bellied lemurs used terminal branches more often while feeding than rufous lemurs. In addition, red-bellied lemurs used the lower middle story forest and rested in taller, upper canopy trees more often than rufous lemurs. Differences in activity and habitat use patterns between lemur species were more related to seasonal changes in food availability than overall differences in group size. These behavioral patterns may represent different strategies used by each lemur species to avoid directly competing for similar resources during times of food scarcity. © 1996 Wiley-Liss, Inc.     

Spatial variations in Eulemur fulvus rufus and Lepilemur mustelinus densities in Madagascar

I present data on variations in Eulemur fulvus rufus and Lepilemur mustelinus densities as well as tree characteristics (height, diameter and stem frequency) between edge and interior forest habitats in southeastern Madagascar. Line transect surveys were conducted from June 2003 to November 2005 in edge and interior forest habitats in the Vohibola III Classified Forest. Although E. f. rufus densities were significantly lower in edge habitats than in interior habitats, density estimates for L. mustelinus did not differ significantly between habitats. Trees in edge habitats were significantly shorter, had smaller diameters and had lower stem frequencies (for those >25 cm in diameter) than trees in interior habitats. Spatial characteristics of food abundance and quality may explain lemur density patterns in Vohibola III. Low E. f. rufus densities may reduce seed dispersal in edge habitats, which has important consequences for the long-term viability of forest ecosystems in Madagascar.     

Effects of Habitat Quality and Seasonality on Ranging Patterns of Collared Brown Lemur (Eulemur collaris) in Littoral Forest Fragments

Degraded forest habitats typically show low fruit availability and scattered fruit tree distribution. This has been shown to force frugivorous primates either to move further in search of food, resulting in large home ranges, or to use energy saving strategies. Malagasy lemurs are known to face pronounced seasonality and resource unpredictability, which is amplified by the overall reduction in food availability due to the human-driven habitat disturbance on the island. To explore lemur flexibility to habitat disturbance, we examined the ranging behavior of collared brown lemurs (Eulemur collaris) in two differently degraded fragments of littoral forest of southeastern Madagascar. We collected data from February 2011 to January 2012 on two groups living in a degraded area and two groups living in a less disturbed forest. We calculated annual ranges, monthly ranges, and daily distance traveled. We then ran repeated measures ANOVAs using seasonality as dichotomous, intrasubject factor and site/group as intersubject nested factors. In the degraded forest, the lemurs had larger monthly ranges, and their annual ranges were either fragmented or characterized by multiple core areas. They were able to use a habitat mosaic that also included nonforested areas and swamps. In addition, they shortened their daily path length, possibly to preserve energy, and used different areas of their annual home ranges seasonally. Although a number of possible confounding factors may have been responsible for the observed differences between sites, our findings highlight the ranging flexibility of collared brown lemurs in littoral forest fragments.     

Ontogeny of conspecific and heterospecific alarm call recognition in wild Verreaux's sifakas (Propithecus verreauxi verreauxi)

The production of vocalizations in nonhuman primates is predominantly innate, whereas learning influences the usage and comprehension of vocalizations. In this study, I examined the development of alarm call recognition in free-ranging infant Verreaux's sifakas. Specifically, I investigated their ability to recognize conspecific alarm calls as well as those of sympatric redfronted lemurs (Eulemur fulvus rufus) in Kirindy forest, western Madagascar. Both species have functionally referential alarm calls for aerial predators and give general alarm calls for both aerial and general predators and also other kinds of threats, such as intergroup encounters with conspecifics. I conducted playback experiments with members of two birth cohorts (nine and ten individuals) to determine the age at which infant Verreaux's sifakas discriminate between conspecific alarm calls, heterospecific alarm calls, and non-alarm vocalizations (parrot song). Most 3-4 months old infants fled toward adults after hearing any playback stimuli, whereas 4-5-month-old infants did so only after presentation of alarm calls. Moreover, all infants of these age classes showed a longer latency to flee after the parrot song indicating their emerging ability to discriminate between alarm calls and non-alarm stimuli. At an age of about 6 months, infants switched from fleeing toward adults to performing adult-like escape responses after presentation of conspecific and heterospecific alarm calls. Thus, the ability to discriminate between alarm from non-alarm stimuli precedes the appearance of adult-like responses. The transition to adult-like escape behavior was coincident with the physical independence of infants from their mothers.     

Morphological Variation in Populations of <Emphasis Type="Italic">Eulemur albocollaris</Emphasis> and <Emphasis Type="Italic">E. fulvus rufus</Emphasis>

Sexual dimorphism in body size and canine weaponry is commonly associated with high levels of male-male competition. When group living species do not rely heavily on male-male competition for access to females, sperm competition may represent a viable alternative strategy. Unlike most haplorhine primates, lemurs are typically monomorphic in body weight and canine height. We assessed variability of body mass dimorphism and canine size dimorphism in brown lemurs using morphometric data from 3 populations in southeastern Madagascar: Eulemur fulvus rufus, E. albocollaris, and hybrids of the species. We found significant male-biased canine dimorphism in E. albocollaris in conjunction with body-size monomorphism. We observed similar patterns in the hybrids, but E. fulvus rufus exhibited significant female-biased size dimorphism and canine monomorphism. Testes volume was relatively high across study populations. Thus, sperm competition appears to be strong in brown lemurs. E. albocollaris males combine sperm competition with large canines, but not higher body mass, indicating a difference in sexual strategy from most lemurs. Patterns of body mass and canine size dimorphism are not uniform across brown lemur populations, indicating that future work on these populations can explicitly test models that predict relationships between size dimorphism and various types of competition.     

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.     

Adaptive and phylogenetic significance of ontogenetic sequences in Archaeolemur, subfossil lemur from Madagascar

Among the best known of recently extinct Malagasy lemurs is Archaeolemur, which is represented by many hundreds of specimens. The phylogenetic affinities of this taxon are unclear, especially in light of recent preliminary analysis of ancient DNA which does not support its previously accepted close relationship with the living Indridae. We examined the nearly complete skeletons of two adults and one juvenile and other less complete specimens to reconstruct aspects of the ontogeny of Archaeolemur. To compare the development of Archaeolemur to that of living strepsirrhines we collected data on Propithecus verreauxi, Eulemur fulvus, and Lemur catta. Additionally, because Archaeolemur exhibits some morphological convergences with distantly related papionins, we tested for convergence in the developmental patterns of Archaeolemur and Macaca fascicularis. Data include the status of tooth eruption, craniofacial sutural closure, and postcranial epiphyseal fusion, as well as linear measurements. We used discriminant function analysis and other tools to explore ontogenetic similarities and differences. The adaptive and phylogenetic significance of ontogenetic information is discussed. Our analysis shows that Archaeolemur displays a clear strepsirrhine pattern of development with only minor macaque convergences. Among the Strepsirrhini, Archaeolemur is slightly more similar developmentally to E. fulvus and L. catta than to P. verreauxi. Some of the distinctive features of the ontogeny of Archaeolemur may be related to diet, while others bear apparent testimony to a relatively rapid absolute pace of growth and development.     

Cathemerality in the Mayotte brown lemur (Eulemur fulvus): seasonality and food quality

In past decades, cathemerality--as defined by Tattersall [1987]--has been documented in two primate families: Cebidae and Lemuridae. In the Lemuridae, in particular the genus Eulemur, cathemeral activity seems to be a regular behavioural trait. Nevertheless, ultimate and proximate determinants responsible for this behaviour remain unclear. In this study, in a dry and deciduous forest on Mayotte (Comoro Archipelago), activities of 4 female brown lemurs (Eulemur fulvus fulvus) were recorded by focal animal sampling during the daylight period and by scan sampling on their respective groups during the night. Horizontal distances travelled by females and groups were measured using GPS. During the daylight period, food intakes were estimated in grams by extrapolation of counting of mouthfuls after weighing a large sample of plant parts eaten. Crude protein, crude lipid, soluble sugar and crude fibre were analyzed for each seasonal reconstituted diet. Records of temperature and rainfall were supplied by a local meteorological station. Observations confirmed cathemerality in the Mayotte brown lemur as reported by Tattersall in 1977. During the dry season, the animals increased their nocturnal activity--substantially increasing the time devoted to feeding and moving overall, but especially at night--and were less active during the daylight period. The quality of their diet in the dry season was poorer than that in the wet season, with soluble sugar content and protein content decreasing and fibre content increasing slightly. As a result, Mayotte brown lemurs may need to extend their foraging activity over the 24-hour cycle to balance nutritional requirements.     

Diurnal resting in brown lemurs in a dry deciduous forest, northwestern Madagascar: implications for seasonal thermoregulation

Decreased activity has been reported in both nocturnal and diurnal primates during the prolonged dry season in western Madagascar, and this has been interpreted as a reaction to the severe environment, with its food scarcity and/or thermal stress. Several day-active lemurs rest more as trees defoliate, although the reason for this is unclear. To understand the mechanism underpinning the diurnal resting of lemurs in seasonal deciduous forests, I observed common brown lemurs (Eulemur fulvus fulvus) for one year in Ankarafantsika National Park, northwestern Madagascar. In Ankarafantsika, despite high fruit availability during the dry season, brown lemurs are known to engage in diurnal resting. To examine the effects of thermal factors and defoliation on lemur inactivity, I recorded the activity of a troop at 1 min intervals, hourly ambient temperature, daily rainfall, and weather during observations (06:00-18:00). I quantified the amount of leaves biweekly for 680 trees. I tested correlations between percentages of resting time and each factor across hours during the day and across seasons. During the rainy season, resting time did not differ between sunny and cloudy days, and lemurs were active throughout the daytime. At the hourly level during the dry season, lemurs rested exclusively at midday, apparently at peak sunlight intensity rather than at peak ambient temperature. At seasonal level, percentages of total resting time from 08:00 to 16:00 were greater during dry season (81.9%) than during rainy season (62.6%), and percentages increased as ambient temperatures increased. Defoliation was related to seasonal decrease in weekly rainfall, which served as an index of water retained in the forest. Defoliation probably reflected aridification as well as the penetration of sunlight into the forest. Diurnal resting increased as both the amount of leaves and weekly rainfall decreased seasonally. These results suggest that heat stress under dry conditions may promote resting. Diurnal resting may function as behavioral thermoregulation to avoid overheating and to minimize water loss via excessive evaporative respiration.