Patterns of elevational distribution of birds and small mammals in the humid forests of Montagne d'Ambre, Madagascar

Abstract

Results are presented of an elevational transect of the slopes of Montagne d'Ambre (summit at 1475 m), extreme northern Madagascar. The forest is classified as humid on the higher slopes above about 600 m and as transitional or dry deciduous below 600 m. Insectivores, rodents, and birds were surveyed at three sites (340, 1000, and 1350 m) along the northeastern slope. Mammals and birds had relatively low species richness when compared to other humid forest sites on Madagascar. Several possible reasons are presented for these differences. The humid forests on Montagne d'Ambre, a geologically recent formation, are currently isolated from similar habitats to the south. During the Late Pleistocene and Holocene Montagne d'Ambre was connected to areas further south by corridors of humid forest. As a result of climatic shifts there has been a drastic change in the lowland habitats of this region.The remaining lowland forests on the moist side of the mountain are transitional between dry deciduous and humid forest. Further.Quaternary volcanic eruptions may have greatly altered the habitat on the upper portion of the mountain. Finally, Rattus rattus has colonized the humid forest en masse and through competitive exclusion or direct predation may be displacing some of the native fauna.