Even though captive individuals of H. g. griseus are known to exhibit nighttime activities (Pollock, 1986; Santini-Palka, 1994), field investigations carried out during daylight hours and nocturnal surveys all suggest that the animals are diurnal (Grassi, 2001; Overdorff et al., 1997; Pollock, 1986; Tan, 2000; Wright, 1986). Except in the degraded forest of Maroantsetra, H. g. griseus individuals have been observed to travel after dusk (16:00-21:00) (Petter et al., 1977). In Talatakely, RNP, a recent study involving 24-hour observations lends further support that the animals are strictly diurnal in the southeast (C. Tan, unpublished data). Daytime activity budget shows that H. g. griseus spends about 41% resting, 48% feeding, and 9% traveling (Figure 1) (Tan, 2000).
H. g. alaotrensis demonstrates cathemerality, or day and night activities (Mutschler, 2002; Mutschler et al., 1998). Although the animals are active mainly during the day, they exhibit significant activity at night that does not seem to be
Figure 1. Activity budget of three sympatric Hapalemur species in Talatakely, Ranomafana National Park.
affected by moonlight conditions. Additionally, year-round nocturnal surveys indicate that they have at least one activity bout per night and each bout lasts ^30 minutes (Mutschler et al., 1998; Mutschler and Tan, 2003).
The activity pattern of H. g. meridionalis and H. g. occidentalis is poorly known. Opportunistic sightings suggest that H. g. meridionalis may be diurnal (Mutschler and Tan, 2003). In Bemaraha and Sambirano, H. g. occidentalis individuals were found to be active primarily at night during the dry season (July-September) (Mutschler and Tan, 2003).
In Talatakely, RNP, H. aureus is diurnal as indicated by 24-hour observations (C. Tan, unpublished data). The activity pattern shows a distinct midday rest period between 09:00 and 13:00. H. aureus spends approximately 54% of the daytime resting, 37% feeding, and 8% traveling (Figure 1) (Tan, 2000).
Petter et al. (1977) suggest H. simus individuals are active only in the daytime. However, in Talatakely, RNP, the animals exhibit a cathemeral activity pattern throughout the year (Tan, 2000 and unpublished data). Diurnal time budget data show that H. simus spends 50% of the time resting, 41% feeding, and 6% traveling (Figure 1) (Tan, 2000).
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