In resent years, the numbers of several waders (Charadriiformes) have decreased in Estonia and elsewhere. The reasons of the decline are indistinct and. probably the causes may be different in different areas. We presume that one of the reasons could be the diminishing (and declined availability) of food resource that may be connected with impoverished soil biota caused by ceased economical management and overgrowing with brushwood of abandoned meadows. As the wader species feed predominately on soil invertebrates, especially earthworms and insects, the investigation will be focused on these communities. As one of the main objectives of the project, the relationship between soil biota and the numbers, territorial distribution and population density of waders will be investigated. According to the working hypothesis, the number, population density and distribution of waders of coastal and floodplain meadows are closely related with the species constitution, abundance and biomass of soil invertebrates communities. At the same time, we assume that the abundance and structure of the earthworm and microbial communities are greatly influenced by water salinity of overfloods. . The study will be carried on the western coast of Estonia, mainly on the coastal and floodplain meadows of the Matsalu Nature Reserve, where the meadows are well represented. In addition to previous counting data on the Matsalu area, additional countings by the standard transect and recurring mapping methods, will also be carried out. Soil invertebrates and microbial communities will be studied by standard and widely known sampling and analysing methods, including certain methods that allow to take into account the spatial parameters and variability. The study will be conducted mainly by the researchers of the Environmental Protection Institute, but several other top specialists from Estonia and abroad will also be involved. The main value of the study relies on better understanding of the relations between the numbers of endangered wader species and their food recourses that will give the basis for better conservation management of the species.