The five year study of species use at the Great Salt Lake allows for a break out of five significant categories of use as birds move through the season (Table 6). These classifications are based on data displayed in the species count charts (see Species Accounts). These categories are departing and arriving winter residents (April and September), migrants to breeding grounds  (April-May), local breeders (April-September), early migrants to wintering grounds (July-August), and later migrants to wintering grounds (August-September). Some species fit within more than one of the categories. A weighted line through the appropriate time periods shows species presence. Line designations are a subjective measurement of the portion of a species population known to be at Great Salt Lake at its peak time. Relative numbers of species by survey period are charted in the Species Accounts.