Altitudinal gradients constitute a powerful test system for understanding the distribution of species around the world. In this book which is based on my Ph.D thesis I strive to untangle basic ecological mechanisms potentially behind avian distribution patterns on Mt. Cameroon. The book focuses on two interrelated themes: avian assemblage structures and selection pressures on life histories. It shows that the avian assemblage on Mt. Cameroon has evolved in relative isolation leading to highly specific avian host- blood parasite interactions and low sexual dimorphism in a monochromatic frugivorous species distributed along the entire gradient probably due to similar ecological space use between males and females in this species. It also shows that the abundance-range size relationship is distorted at higher elevations toward the montane forest because restricted-range species are very abundant. This book shows the influence of the environment on the ecology of birds, and opens thepath for more stringent investigations on Afrotropical Mountains.