Sentence:  There are only two ways to remedy the mute-swan situation: Pay people to locate nests and addle their eggs (<WSD>"addling</WSD>" means shaking each egg hard to kill the embryo inside; if you smash the eggs, the birds will lay replacements, but swans will sit on addled eggs and not lay more), or authorized licensed hunters to shoot the birds. <WSD>Addling</WSD> is not only time consuming and expensive, but it's also dangerous because swans regard people who invade their nesting territory as just a larger kind of raccoon. 
Meaning of the word marked with <WSD> tags:  The act of causing fertilised eggs to lose viability, by killing the developing embryo within through shaking, piercing, freezing or oiling, without breaking the shell or other outer layer.