When swallows scratch the surface

FOR years, I’ve watched swallows flying over water and dipping the ends of their beaks into the surface. I assumed they were getting a drink on the wing.

House martins and sand martins do it, too. All three species are related and the speed and precision with which they fly puts them in the top ranks of avian aviators. These hirundines (their scientific name), are supposed to feed exclusively on flying insects they catch on the wing. I’ve been watching them more closely this summer, and I think ‘exclusively’ is incorrect.

I don’t think they are drinking when they dip their lower beaks into water, I think they’re feeding. I first suspected this from the frequency with which they do it. This was not consistent with slaking a thirst. I got out the binoculars to have a closer look and went out in a boat to examine the water surface. I found large numbers of chironomids floating on the surface. Chironomids are non-biting midges and their life cycle involves a larval stage that is spent under water; before they pupate, rise to the surface, and hatch into winged insects.