Ospreys eat fish as their main source of sustenance and focus on whichever species are abundant in their area, such as flounder, smelt, mullet, bullhead, sucker, and gizzard shad. These birds very rarely eat small mammals, birds, or reptiles (usually only when no fish are available). Ospreys were once endangered by pesticide use, but after DDT was banned in the 1970s, their numbers have improved considerably.