A COMPARATIVE-STUDY OF THE RANGING BEHAVIOR, ACTIVITY RHYTHMS AND SOCIALITY OF LEPILEMUR-EDWARDSI (PRIMATES, LEPILEMURIDAE) AND AVAHI-OCCIDENTALIS (PRIMATES, INDRIIDAE) AT AMPIJOROA, MADAGASCAR

Lepilemur edwardsi and Avahi occidentalis are both small, nocturnal fo livores, but live sympatrically over a large part of their range, sugg esting that niche differentiation has occurred. In order to establish whether ranging behaviour and activity patterns have contributed to ni che differentiation, a field-study was carried out at Ampijoroa, Madag ascar, within the area of range overlap. Four individuals of each spec ies were fitted with radiocollars and tracked, dusk to dawn, over 18 m onths. Data were collected on home-range size, travel distances, activ ity and social behaviour. Neither showed the markedly biphasic activit y patterns which have often been described for nocturnal prosimians; t his might be explained by the combination of folivory and small body s ize. L. edwardsi spent long periods inactive, but engaged in considera ble social interaction during the night, including extensive long-rang e calling. The mean home range was 1.09 ha, and ranges were rather eve nly used. Home ranges of females overlapped extensively, and the range of the single adult male which could be caught overlapped with the ra nges of several females, as is common in nocturnal prosimians. The mea n nightly travel distance was very low, only 343 metres. On the other hand social interactions in A. occidentalis were primarily within a st able monogamous family unit, and long-range calling was very limited. Home ranges were rather larger than in L. edwardsi, but less evenly us ed, and mean nightly travel distances were much greater, 1175 m. Diffe rences in range-use patterns may be explained by the contrast between Avahi's selective feeding on relatively high-quality young leaves and flowers, versus Lepilemur edwardsi's unselective feeding on relatively low-quality, but ubiquitous and evenly-distributed, mature and old le aves. Similarly, while overlapping female ranges may be adequate when food resources are evenly distributed, monogamy in Avahi may be a resp onse to selective feeding on a patchy food resource.