It's Not a Bug, It's a Feature
I had never seen skimmers before finding a small group feeding at Huntington Beach State Park while visiting South Carolina. In most birds, such a disparity between the length of the upper and lower bill would be a defect, but in skimmers it’s there by design.
Skimmers feed by flying just above the water and skimming the surface with their bills. As the skimmers were feeding that day, you could see little fish jump out of the water to evade the hungry birds.