Supporting information S1 Table. Method of diet analysis of diets retrieved from the literature. The column labelled "Code" is used in S2 Table. (DOCX) S2 Table. Diet **data** as retrieved from the literature. Including information pertaining to the species studied, the study reference, the location in which the study took place, the number of individuals sampled, the study method (See S1 Table), and the diet data. See S2 Table. (CSV) S3 Table. Criterion used in categorizing guano particle size (a) and colour (b).