Good question. The reason that the swans may kill their young is not necessarily the survival of the fittest, but more to either put them out of their misery, keep predators from being attracted and catching up to the rest of the brood, or a means to keep an illness from infecting the rest of the brood.

Unfortunately, we have see in our 10 year research, several instances where the male parent chased an injured or ill cygnet from the fold. When the bird attempted to come back, the male tried to kill the cygnet. We intervened in a couple of instances to see what the problem was with the cygnet and found either a severe injury due to an alligator attack (with surgery the cygnet did survive, but could not be placed back with the family), and in the other situation, the cygnet was dying from egg sac peritonitis which ultimately kill the bird. So, infanticide as rare as it may be, does occur in some instances.

On another note, other swans in the area will also attack and kill cygnets from other families if the cygnets enter a territory that has been established by other swans. We hope that this information is of benefit. The Regal Swan