Least Terns have their enemies. Pilots especially. The birds tend to nest near airports, and on flat spaces near runways. They have no fear of airplanes and often fly right underneath taxiing aircraft. A bird sucked into an aircraft intake can result in a crash.
Lots of different measures have been tried to discourage them, but they are only moderated effective. As a result, sometimes pilots and those associated with aviators resort to more direct methods to keep the populations down.
I can recall one case back in the early 1980s when an ABHC was quietly and quickly retired after it was learned that he had led a group of sailors on an unauthorized mission to reduce the tern population of a NAS.
Not sure if it is the case, but I would bet that something similar to that is at least partially involved.
Move the airports...