Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Figure 1. Variation in mean monthly nocturnal and diurnal activity (± SE) in E. mongoz at Anjamena, northwest Madagascar (16°03'S; 45°55'E) during a 10-month field study in 1994-1995 (Curtis et al., 1999) and annual changes in the light/dark ratio (Thomas and Curtis, 2001). Nocturnal activity is maximal and diurnal activity minimal around the austral winter solstice (AWS) when daylength is shortest. The austral autumnal equinox (AAE) occurs just prior to the shift from predominantly diurnal activity to predominantly nocturnal activity and the austral spring equinox (ASE) just before the shift back to mainly diurnal activity. The peak in nocturnal activity in November may be connected to predator avoidance, as this coincides with part of the raptors nesting period at Anjamena, low canopy cover, and the onset of infant mongoose lemurs' independent movements (Curtis et al., 1999).

Mode A describes the alternation of day (austral summer) and night activity (austral winter) and has only been observed in E. mongoz in the seasonally dry forests of western Madagascar (Figure 2a,b) (Tattersall and Sussman, 1975; Sussman and Tattersall, 1976; Harrington, 1978; Andriatsarafara, 1988; Curtis et al., 1999; Rasmussen, 1999, 2005). The pattern of activity peaks changes from bimodal during austral summer to trimodal during austral winter.

Mode B describes the shift from diurnal activity during the austral summer to 24-hr activity during the austral winter (Figure 2c,d) and is observed in E. f. ful-vus and E. f. rufus in seasonally dry forest (Donati et al., 1999; Rasmussen, 1999; Kappeler and Erkert, 2003), E. f. collaris in non-seasonal littoral rainforest (Donati and Borgognini-Tarli, 2006) in Madagascar, and E. f. mayottensis in seasonally dry forest on Mayotte (Tarnaud, 2006). Depending on the species and study area, the activity pattern is bimodal or trimodal during the austral summer and trimodal or quadrimodal during the austral winter.

Mode C describes 24-hr activity all year round, with trimodal and/or quadri-modal activity patterns during both the austral summer and winter (Figure 2e,f). This mode is observed in E. macaco macaco, E. rubriventer, E. f. rufus in coastal

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