Unfortunately, the cygnet is not going to survive. The parents may try to kill it as they know something is wrong. We have seen this time and time again. The parents know when something is wrong and even if you were to intervene by capturing the cygnet and calling Swan Lifeline in Eton, there are no guarantees that the young bird will survive. If the young cygnet cannot keep up due to its being ill or being the runt, the parents will not sacrifice the rest of the family to an illness/disease or picked off by a predator. The smallest and sickest will be dispatched with no bonding attachments like in humans. This is nature and is how specific animals and other species survive. If you still want to intervene and the cygnet is alive tomorrow, we would suggest that you contact Wendy Hermon at Swan Lifeline to see if someone can try to affect a rescue. The Regal Swan