 because that is what they shout. Then they surround the swans and lift them up, hence the title, assessing their health and weighing them. The swan marker takes all the swan notes, and then they put the swans down and row off and pick more swans up, all the while doing their best not to get concussed by these exquisite, elegant, furious, violent, brutal, deranged, homicidal birds. See? It is normal.