Keywords: black skimmers seabird bill shape animal behavior mandible structure douglas barnum/usgs barnumusgs outdoor No fishing net required! Black skimmers have an uncommonly long lower mandible, which they use to skim the water. When they hit a fish, their bill snaps shut immediately to grab the fish. These seabirds can be found in national marine sanctuaries throughout the southeast United States. Have you spotted one? Photo Credit: Douglas Barnum/USGS No fishing net required! Black skimmers have an uncommonly long lower mandible, which they use to skim the water. When they hit a fish, their bill snaps shut immediately to grab the fish. These seabirds can be found in national marine sanctuaries throughout the southeast United States. Have you spotted one? Photo Credit: Douglas Barnum/USGS |