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

Abstract

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.

Behavioral flexibility of vervet monkeys in response to climatic and social variability

“…We do know that, at high temperatures, some studies have revealed that animals tend to spend more time resting (Stelzner, 1988;Hill, 2006;Campos and Fedigan, 2009;Korstjens et al, 2010;Sato, 2012;Majolo et al, 2013), and that resting and shade-seeking are critical for thermoregulation (e.g., Campos and Fedigan, 2009): high heat load can cause severe dehydration and potentially fatal hyperthermia (Taylor, 1970). In contrast to the reduced demand for shade-seeking and resting in colder temperatures, the energetic demands of thermoregulation and digestion are higher in cold conditions (Satinoff, 2011), meaning more time needs to be spent feeding (Satinoff, 2011;Majolo et al, 2013).…”

The influence of some ecological factors on drill monkeys Mandrillus leucophaeus (Cuvier) - in Limbe wildlife center (LWC), Southwest Region, Cameroon

“…Direct weather constraints on activity budgets have received little attention. It is known that at high temperatures, some the animals tend to spend more time resting (Hill, 2006;Campos and Fedigan, 2009;Korstjens et al, 2010;Sato, 2012;Majolo et al, 2013), and that resting and shade-seeking which are critical for thermoregulation (Campos and Fedigan, 2009): high heat load can cause severe dehydration and potentially fatal hyperthermia. In contrast to the reduced demand for shade-seeking and resting in colder temperatures, the energetic demands of thermoregulation and digestion are higher in cold conditions, which mean that more time are needed to be spent on feeding (Satinoff, 2011;Majolo et al, 2013).…”

“…Many studies have shown that the activity budgets vary by several environmental factors include diet, distribution and food sources (Passamani, 1998). It has been shown that the activity budgets of the species are influenced by several environmental factors, such as weather season as well as distribution and food sources (Passamani, 1998;Sato, 2012;Oates and Butynski, 2008). Studies of activity budgets in drill monkeys have shown that, the time spent in different activities vary diurnally and seasonally within age sex class groups in the rainforest and shrub land habitats.…”

Proximity association in polygynous western black crested gibbons ( Nomascus concolor jingdongensis ): network structure and seasonality

“…Theropithecus gelada : Dunbar, 1998; Symphalangus syndactylus: Kim et al, 2011; Eulemur fulvus fulvus: Sato, 2012; Nomascus concolor jingdongensis . In our study, we found that temperature significantly influenced group proximity, with individuals spending more time in spatial proximity when the temperature was low.…”