Torn webbing could indicated turtle or other predator attack. Is there any indication of pellets or lead shot? This would indicate a swan that has been shot. The swollen bones could mean a bone infection and the bird would need to be placed on an antibiotic, which would not be a bad idea anyway.

If the bird was sitting somewhere by itself and not moving, it would indicate that something is wrong with the foot. The swan is probably in pain, so have your veterinarian not only do a blood test to see if there is an infection, but also provide Medicam to provide it relief from pain.

In about a week, or when the antibiotic regimen ceases, re-check the blood to ensure that the infection has been fully treated and another antibiotic not needed.

There is also the possibility that something stepped on the bird, it ran into something, snakebite, or yes, just a birth defect. As long as blood tests have been conducted, a round of antibiotics and pain killer provided and the bird looks like it can place weight on the foot, then it should be okay. The major issue is to make sure there is no other infection or something else wrong with the bird. Make sure it is eating, if not, supportive care such a tube feeding 2-3 times a day along with one shot (one dosage of B12) provided to keep its appetite. The Regal Swan