Observations éco-éthologiques sur deux lémuriens malgaches nocturnes : Phaner furcifer et Microcebus coquereli

Abstract

A study carried out at three sites in the western coastal forest of Madagascar, especially in the Morondava area, provided the authors with substantial information about the behaviour and ecology of the Fork-Crowned Lemur (Phaner furcifer) and Coque- rel’s Mouse Lemur (Microcebus coquereli). The two nocturnal species, which have roughly the same body-size, are still relatively undocumented. A survey of the collections permitted determination of the geographical distribution of the two species ; they seem to be limited to the more humid zones of the west coast forest. Phaner also occurs on the Montagne d’ Ambre and at least in the North- East region of the eastern coastal forest. In the two latter areas, however, the species in represented by a large form which should probably be regarded as a separate sub-species. The western habitat is characterised by a hot, dry climate with rain concentrated in the period December-March and a period of relatively severe dessication from September to December. At this time, the majority of the trees loose their leaves. In these forest areas, one can find up to 8 lemur species, two of which ( Lepilemur mustelinus and Microcebus murinus) are also nocturnal. Both Phaner and Microcebus coquereli can be found in spherical leaf-nests constructed with intertwined, leafy branches ; but it is apparently only the Microcebus which constructs these nests. Both species have roughly the same activity rhythm, which seems to be closely correlated with the ambient light intensity. Precise measurements of the activity of the animals and the light intensity at onset and cessation of activity permitted detailed exa mination of this correlation. Phaner moves around very rapidly by running and leaping on branches with its body maintained horizontal ; the keeled nails allow the animal to cling to trunks. Microcebus coquereli, which is less rapid, remains relatively close to the ground by preference and maintains its body vertical most of the time, frequently moving by leaps from one trunk to another. The Phaner are among the noisiest of the lemurs. Their vocal activity persists throughout the night, but it is noticeably more intense during the first quarter-of-an-hour. Coquerel’s Mouse Lemur is much more discreet. Phaner possesses a pronounced marking-gland on the ventral side of the neck, and this is used to « mark » certain trunks in the home range. No marking behaviour was seen with Microcebus coquereli. The home range of Phaner covers roughly one hectare (2,5 acres), but this is shared with a dozen others. Usually, the diffe rent individuals move separately from one feeding-placc to ano ther, any encounter normally leading to violent vocalisation, chases and sometimes severe fighting. Microcebus coquereli, which is very rare, is also more difficult to follow at night, and no precise observations could be made to permit estimation of the size of the home range. Phaner occurs at very high population densities, ranging from 650 to 850 individuals per km2, whilst both Microcebus coquereli and Lepilemur can be estimated as occuring in densities of 250 and 300 individuals per km2. The most striking feature of Phaner resides in its diet. At least during the dry season, it is à consumer of resins and insect secretions. This special diet can be correlated with certain notable anatomical features : extensive adaptation of the incisors, premo lars and molars ; adaptation of the digestive tract (relatively well developed) ; adaptation of the tongue, which is long and pointed. Microcebus coquereli adopts a diet partially allied to that of Phaner during the dry season, but it retains a pronounced insec tivorous tendency. The high density of Phaner can be explained through its unu sual diet. From a dietary point of view, it probably undergoes no more than weak interspecific competition during the dry season. This does not apply to Microcebus coquereli, which is in fact competing with Microcebus murinus and numerous insectivorous birds. It is possible that there is competition between Phaner, Micro cebus and Lepilemur for hiding-places. It is interesting to note that there is no obligatory relationship of this kind, in that Lepi lemur is not less numerous in areas where Phaner occurs than in areas where it is absent. The anomalous geographical distribution of the two species studied is probably related to climatic or vegetational peculiari ties ; but it is perhaps necessary to invoke as well influences exerted by interspecific competition and predation (in relationship with the vulnerability and fecundity of the two species).

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