The barn swallow is an endangered species, but at CONO dairy farmer Pieter Jan in Middenbeemster they are safe. Every year, around twenty pairs of barn swallows brood in the barns. Insects are the swallows' favourite food, and that is just as well! Cows are irritated by flies and therefore wag their tails all day long. Swallows eat a large part of the flies. Thousands a day! They are so satisfied with their shelter that they come back every spring. And always in the same place: at the top of the sandpit where the cows can roll around.

"The swallows found us immediately when the new farm was built here," says Pieter Jan. "The extra animals are fun, but also very useful. Apart from reducing the number of flies, they protect the cows against an invasion of starlings. Starlings live in large groups of up to ten thousand individuals. They have a nose for good food, such as the maize we give our cows. A swarm of starlings regularly flies into the barn. Two things happen then: they eat the feed and defecate in the feeding troughs. Of course, we don't want that to happen, because there is a risk of disease. Fortunately, the barn swallows are able to chase the starlings away in no time.