Addling

The familiar hatchery practice of agitating the eggs after they are eyed, called shocking or addling, ruptures the yolk membranes of the ever-tender sterile eggs. The result is a precipitation of the globulin and a whitening of the egg.

Egg addling was important in several species, but it was not recorded what proportion of the unhatched eggs were fertile. Compared with the amount of egg addling in some other birds, the amount among raptors is often high. In part this addling is linked with food conditions, as mentioned, and perhaps with the nutritional state of the female.

There are only two ways to remedy the mute-swan situation: Pay people to locate nests and addle their eggs (addling 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. Addling 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.

[I]n 1999, we issued regulations for a special Canada goose permit to provide state wildlife agencies the ability to manage and control resident population Canada geese. These permits can authorize addling of eggs from March 11 through August 31.

Addling accounted for 1% of clutches laid, 1% of all nests, and 2% of all complete failures. […] In most addled clutches all the eggs remained intact, but in some, one or more eggs were broken during incubation. […] [W]hile some egg addling was due to pollutants, other addling was probably due to natural factors.

Physical methods are sometimes used to reduce or eliminate fertility. Methods include physical addling and surgical sterilization. Meaning "loss of development," addling in the strictest sense is destruction of eggs by shaking. Addling has come to mean destroying eggs by any physical or chemical means – puncturing, freezing, or coating with vegetable oil.