Seasonal variation in stomach contents and diet composition in the large girdled lizard, Cordylus giganteus (Reptilia: Cordylidae) in the Highveld grasslands of the northeastern Free State, South Africa
Cordylus giganteus is endemic to the Highveld grasslands of South Africa. Owing to limited distribution and extensive habitat destruction, it may be regarded as an endangered species. C. giganteus individuals fed during eight months of the year. The mass of food in the stomachs and remains in the hind guts indicated that a high degree of foraging success occurred during the warm spring and summer months in association with seasonal variation in resource abundance. Analysis of the contents of 480 stomachs revealed that the diet of C. giganteus in the study area consisted almost exclusively of arthropods, with six of the major taxa (Coleoptera, Diplopoda, Hemiptera, Hymenoptera, Orthoptera and Lepidoptera) accounting for 80 % of the total number and 90 % of the gravimetric contribution of ingested food by the different age and sex groups. Coleoptera dominated as prey category throughout the seasons. The consistency of the main food categories in spring, summer and autumn suggest that prey selection took place, and that C. giganteus is opportunistic only in the sense of taking other prey taxa when they are present in greater abundance. All the major prey types in the diet showed negative relationships between relative abundance and selectivity, indicating that C. giganteus preferred a prey type more when it was relatively less abundant in the environment. Measurement of dietary overlap for prey taxa indicated a high degree of dietary similarity for all age and sex classes.