In total, we identified 80 published studies, many of which used different methods of determining diet (described in S1 Table), this resulted in a **dataset** of 212 diets spread across 17 species. For more information regarding the diets, including country of sample collection, references, the study method, and the collated literature data, please see (S2 Table). For the purpose of this study, the **data** are expressed in number of diets rather than number of studies, as each study may present more than one diet. Each individual reference may present the diets of different species, present the diets of one species measured in different ways, or diets of one species from different sampling locations or seasons. Prey taxa were grouped by order (where possible), class, phylum, or kingdom (where necessary). The mean of all of the diets for each species was calculated. When directly comparing with guano morphology M. alcathoe was dropped from the **dataset** as there was no guano samples available with which to compare. Once a count of the taxa identified by each study had been recorded for each study, the results of each publication were collapsed to order level to allow comparison of the studies (S2 Table).