The White-faced Ibis in the United States breeds west of the Mississippi River and south of the 45th parallel (A.O.U. 1983), with the majority nesting in the Great Basin states (Ryder 1967). Historically in Idaho, it has been considered a casual summer visitor and irregular breeder (Larrison et al. 1967, Ryder 1967, Burleigh 1972). In this paper we show that while there were very few records of the White-faced Ibis for the state until the early 1960s, numerous active nesting colonies in Idaho are now known. We also document and describe the foraging of thousands of postbreeding ibises on the extensive mudflats of American Falls Reservoir, which, unlike sites described elsewhere (Bray and Klebenow 1988), were used daily throughout late summer.