The flood plain of the Medveditsa River in the middle current is characterised by various fauna of birds. Nowadays significant transformations of local fauna, influenced by climatic conditions and anthropogenous loadings, are observed. In the valley of the river the most significant factor influencing communities of birds is the flood mode. The purpose of the work is the birds faunogenetic structure analysis of the Mededitsa river flood plain, and also it`s dynamics under the conditions of degradation of an inundated hydrological cycle. Collecting field data was carried out on the territory of the Medveditsa River valley between the Uritsky village (55.43 ° EL of 44.93 °N) and Atayevka village (51.17 ° EL 44.50 °N) of Lysogorsky district of the Saratov region in May-July, 2013–2016. The methods of research included the birds quantitative accounting, mapping of nesting sites, selection the faunogenetic complexes, determination of the birds residence status in habitats. Assessment of statistical similarity of species quantity in various ecological groups of birds under the conditions of the changing water content of a flood plain was carried out by means of Mann-Whitney nonparametric U-criterion. During the observations period the manifolding of 117 bird species which are falling into nine faunogenetic complexes was confirmed. According to their ecological adaptations birds fall into dendrofila, limnofila, sklerofila, types of open spaces, evritopa and sinantropa. The species having relationship with the European broad-leaved woods, Palearktik's woods, as well as widespread azonal palearkta, prevail among them. Representatives shares of the Mediterranean, Manchurian, steppe and desert and taiga fauna are small. The Arctic and hypoarctic birds meet in the Medveditsa River valley during seasonal migrations. Degradation tendency of the annual Medveditsa River hydrological cycle was identified: a frequency of anomalously low floods is ascending and abundantly high waters occur once in seven-ten years. As a result, we observe Essential structural change of habitats the limnophilic of the birds dated for reservoirs of the central flood plain and a priterrasye. The analysis of the U-criterion calculated by quantity of the nesting in different years limnofila, dendrofila types and birds of open spaces, showed that water content of a flood plain does not influence significantly the structure of birds communities (U emp > U0.05). We identified a certain difference (U emp< U0.01) in quantity of breeding individuals of the limnofila birds in the years with the maximum and minimum levels of the priterrasny Lebyazje lake on the model platform.