There may be something wrong with the swan and if it has a wing problem and cannot fly, you are correct in that the bird could be easy prey for a predator.

You need to check your state's wildlife laws regarding Mute Swans. Many states will kill the bird or threaten wildlife rehabilitation facilities/rehabbers and even veterinarians with loss of permits if they treat a Mute Swan. If this is not the case in your state, we would suggest that you discretely call a wildlife rehabilitation facility/rehabber to see if they can help capture, exam and treat the bird. If there is a significant wing injury that the bird cannot fly, then they can possibly help find a home for the swan so that it can live in a protected secure forever home.

If the swan can fly even a little, capture may be impossible, so you will need the added support of someone who has captured swans and has the proper equipment so that the swan or the rescuers do not get hurt by the wings. Please let us know how this situation progresses. Thank you for caring for the swan and wanting to intervene to save it. The Regal Swan