The prey displayed to mates and delivered to chicks by nesting Gull-billed Tern (Sterna nilotica) was studied in a colony on a coastal lagoon in eastern Spain during 2003. During 31 hours of observations, 1,091 prey items were observed. The trophic resources exploited by the species and seasonal differences in prey composition within the same breeding season were examined. Red Swamp Crayfish (Procambarus clarkii) was the main prey species (64% of prey items), followed by insects (17%) and fish (6%). The proportion of terrestrial prey taken was low. Proportionately more aquatic prey was brought to the colony during courtship-period and chicks were fed proportionately more aquatic prey earlier in the season. The proportion of vertebrate and invertebrate prey did not change significantly during the season. The prey observed in the study suggests that the Gull-billed Terns foraged mostly in rice fields.