This study aims to select piscivorous bird species to be used as indicators to monitor changes in fish diversity at the Banc d'Arguin, Mauritania. Such species should have a high diet diversity, low dietary overlap and data should be easy to collect. We compared the diets of five colony nesting bird species at the Banc d'Arguin: the Slender-billed Gull Chroicocephalus genei, Caspian Tern Hydroprognecaspia and Royal Tern Thalasseus maximus albididorsalis, which are part of an ongoing monitoring program, and the White-breasted Cormorant Phalacrocorax carbo lucidus and Mauritanian Spoonbill Platalea leucorodiabalsaci as potential new additions. All species considerably differed in prey species composition, prey species diversity and prey size. Diet overlap indices varied between 0.05 and 0.69 with the highest overlap values between Mauritanian Spoonbill and Slender-billed Gull. There are major differences between the species in ecological and behavioural mechanisms promoting diet segregation, such as foraging habitat use, foraging ranges and prey-catching techniques. We conclude that the species investigated serve our monitoring goal well. Practical recommendations for the implementation of a monitoring program are given.