Black-headed Gulls Chroicocephalus ridibundus capturing chironomids in flight: have flight costs been overestimated?

Abstract

The diurnal and seasonal occurrence of flight foraging for midges (Chironomidae) by Black-headed Gulls Chroicocephalus ridibundus was studied at a shallow semi-eutrophic lake in South Sweden and their capture rates were recorded. The gulls captured 0.28 chiromids s(-1) (1,012 h(-1)). With a dry mass of 2.08 mg ind(-1) and an energy content of 22.7 kJ g(-1), they achieved an energy intake of c.47 kJ h(-1). It seems that estimates of flight costs may have been over-estimated, and it is concluded that aerial feeding on chironomids by Black-headed Gulls results in a positive energy balance.