While studying nesting Tree Swallows (Iridoprocne bicolor) at the University of Michigan Biological Station in the summer of 1952, I found evidence that the adult birds were feeding their young on fresh-water snails and clams. A number of snail shells and one clam shell were found among the fecal sacs which accumulated in the nests during the last few days before the young left the nest. Each snail shell showed signs of chemical action on the surface and was filled almost to the tip of the spire with fecal matter. To test the assumption that snail shells would be recovered in this form after passing through the digestive tract of a swallow, a young Purple Martin (Progne subis)–the only species then available–was fed eight snail shells of the size of those found i the Tree Swallow nests. Within 16 hours four of these snails had passed through the digestive tract of the Purple Martin to be deposited separately from the fecal sacs. They were nearly identical in appearance to the shells found in the Tree Swallow nests. Seven of the 26 Tree Swallow nests studied at the Station contained these shell remains. The shells were identified by Dr. Frank E. Eggleton, of the University of Michigan, as Physa sayi, P. gyrina, Helisoma antrosa percarinatum, and Sphaerium sp. These species were all abundant within a half mile of the nesting boxes, inhabiting shallow water areas and occasionally emerging on the vegetation or wet sandy beaches. The swallows may have picked up the mollusks from the beach, from vegetation, or from the surface of quiet water. Dr. A. L. Nelson, Director of the Patuxent Research Refuge at Laurel, Maryland, has kindly notified me that there are a few unpublished records of unidentified mollusks eaten by several species of swallows.