Hiding from the Moonlight: Luminosity and Temperature Affect Activity of Asian Nocturnal Primates in a Highly Seasonal Forest

Abstract

The effect of moonlight and temperature on activity of slow lorises was previously little known and this knowledge might be useful for understanding many aspects of their behavioural ecology, and developing strategies to monitor and protect populations. In this study we aimed to determine if the activity of the pygmy loris (Nycticebus pygmaeus) is affected by ambient temperature and/or moonlight in a mixed deciduous forest. We radio-collared five females and five males in the Seima Protection Forest, Cambodia, in February to May, 2008 and January to March, 2009 and recorded their behaviour at 5 minutes intervals, totalling 2736 observations. We classified each observation as either inactive (sleeping or alert) or active behaviour (travel, feeding, grooming, or others). Moon luminosity (bright/dark) and ambient temperature were recorded for each observation. The response variable, activity, was binary (active or inactive), and a logit link function was used. Ambient temperature alone did not significantly affect mean activity. Although mean activity was significantly affected by moonlight, the interaction between moonlight and temperature was also significant: on bright nights, studied animals were increasingly more active with higher temperature; and on dark nights they were consistently active regardless of temperature. The most plausible explanation is that on bright cold nights the combined risk of being seen and attacked by predators and heat loss outweigh the benefit of active behaviours.

A remarkably quick habituation and high use of a rope bridge by an endangered marsupial, the western ringtail possum

“…A higher risk of heat loss could be another reason for possums to cross the bridge less on windy nights (McCafferty et al 2011); however, this is unlikely to be the case given that the number of crossings actually increased on colder nights, contrary to our expectation. It seems that heat loss is not as big problem for P. occidentalis as for other arboreal mammals studied by Laurance (1990), Starr et al (2012), and Rode-Margono and Nekaris (2014). These researchers studied species in tropical regions such as Northern Queensland, Cambodia, and West Java, and their study species might have been more susceptible or less adapted to cold conditions compared to P. occidentalis.…”

“…Other arboreal folivorous species have been observed to be less active on well lit nights with low temperatures, presumably to avoid the risk of predation and heat loss (Laurance 1990, Starr et al 2012, RodeMargono and Nekaris 2014. Greater wind speed also decreased the number of common brushtail possums (Trichosurus vulpecula) observed in open pasture (Paterson 1993).…”

Cathemerality in a small, folivorous primate: proximate control of diel activity in Hapalemur meridionalis

“…lunar luminance or environmental variables) can override endogenous circadian rhythms by inhibiting or enhancing activity (Erkert 1989;Chiesa et al 2010). Decreasing activity with increasing lunar illumination (lunarphobia) is common in many mammals (Penteriani et al 2011;Prugh and Golden 2014), including carnivores (Halle 2000;Packer et al 2011), bats (Erkert 1974(Erkert , 1976Saldaña-Vázquez and Munguía-Rosas 2013), rodents (O'Farrell 1974;Kaufman and Kaufman 1982;Corsini et al 1995;Upham and Hafner 2013), and primates (Bearder et al 2006;Starr et al 2012;Rode-Margono and Nekaris 2014). Conversely, relatively few mammals display lunarphilia, i.e.…”

Densities, distribution and detectability of a small nocturnal primate (Javan slow loris Nycticebus javanicus) in a montane rainforest

“…Trent et al (1977), in a study of captive animals, reported greater slow lorises to be lunar phobic. Starr et al (2012) reported that wild pygmy slow lorises were clearly lunar phobic during the dry cool season, but showed lunar neutrality during the colder wet season. For wild slender lorises Loris tardigradus, Bearder et al (2002) noted that they called more frequently during moonlit nights and that they increased foraging and travelling during full moon, suggesting that slender lorises are lunar philic.…”

“…speed at which surveys are conducted) both strongly influencee detectability, again possibly more so during the night than in the day. As noted by Starr et al (2012) the sensory world of the forest at night has strongly influenced the behaviour and physiology of nocturnal mammals. In the absence of visual sensory cues, the activity patterns of many nocturnal mammals are affected by the intensity of nocturnal illumination.…”