This is a common condition in raptors especially Falcons, several factors are involved however the main causal agents are:
- Pressure sores
In essences bruising or abrasions result in damage to the skin on the underside of the foot.
Bacteria are then able to get into the foot, replicating and setting up an infection, this infection is then able to track up into the deeper tissue.
If allowed to extend into joints or around tendons these areas /tissues then become improvably damaged, resulting in significant permanent damage to the digit/foot.
As with all diseases and conditions affecting Birds early detection is the key.
Daily checks of your Birds are essential, especially of all the underside of digits and Feet.
Good hygiene of perches, and the provision of a variety of perch types and different dimeters are key in preventing this issue.