What is an early warning sign of bumblefoot in raptors?

An early warning sign of bumblefoot in raptors is associated with the condition's impact on a bird's health and overall behavior. While low blood sugar can affect a bird's energy levels and may result in some behavioral changes, bumblefoot specifically often manifests through visible signs of injury or illness, such as swelling on the feet, rather than metabolic issues alone.

In contrast, the other options do not directly relate to the symptoms of bumblefoot. Weight gain would indicate good health and feeding, excessive vocalization could stem from various causes, including stress or breeding behavior, and increased activity usually signifies a healthy bird rather than one that is suffering from bumblefoot. Thus, while low blood sugar can cause seizures or fits, it does not align with the typical early indicator of bumblefoot, which requires careful observation of foot health rather than general behavioral changes.