The reduction of wetlands is an important cause of conservation concern since some specialist, vulnerable and rare species live in these habitats. Although several investigations on bird communities of fragmented wetland have been carried out, studies on the effects of specific disturbance factors on bird populations and communities of wetland are scarce. In this study the effects of water level oscillation on bird populations of a wetland were investigated. Bird communities were monitored by means of mapping census method in the wetland and surrounding open habitats of a Central Italy study area for two consecutive breeding seasons (2001 and 2002 springs). In the second year the reduction of rainfall dramatically lowered the water level. Species richness, diversity, abundance, and biomass values decreased from 2001 to 2002. This was related to the significant reduction of density of the bird species associated to the reedbed and wet habitats. Except for Anas platyrhynchos and Acrocephalus scirpaceus, all species of reedbed and aquatic habitats were absent in the spring 2002. Change in richness and in relative frequency of the species in two years, due to disturbance induced by the water level oscillations, were highlighted by diversity/dominance diagram. The results suggest that conservation actions for remnant wetlands should take into account the problems related to the water cycles at multiple scales.