I was recently at Merritt Island in Florida and discovered this Black Skimmer zipping along on the water surface of one of the inland canals.  Their behavior is as unique as  their appearance.  They have scissors-like red bill and their lower bill is much longer than the upper bill.  They skim along the surface, scooping fish into this brightly colored bill.  As I followed this bird in flight, it dove under the surface and tucked it’s head under as it came back up above the surface.  I have no idea what purpose this head tucking  behavior serves.  If you know about this behavior, please share with me!