Chick growth and prey quality in the European Bee-eater (Merops apiaster)

1. In each of four replicate experiments we fed three groups of bee-eater chicks for 24 h on different diets: bees, dragonflies, and a mixture of the two. 2. Dry weight assimilation efficiency did not differ between treatments and was in the region of 40-50%. Caloric assimilation efficiency was about 60% and did not differ significantly between diets. 3. Mean Growth efficiency (wt. gain/intake) was highest in all four replicates in chicks fed on the mixed diet. 4. When metabolic requirements are taken into account, growth efficiency on the mixed diet varies less with variation in intake than on the two pure diets. 5. The advantage of feeding chicks on a mixed diet may partly explain why parents do not show exclusive preferences for energy-maximising prey types.