What issue do passage kestrels face that may affect their suitability for apprentices?

Challenges in weight management are a significant issue for passage kestrels that can affect their suitability for apprentices. Managing a bird's weight is critical for successful falconry, as it influences the bird’s hunting ability, responsiveness, and overall health. Passage kestrels, which are young birds captured after migrating, can be particularly sensitive to fluctuations in weight because they are still adjusting to human interaction and the demands of falconry training.

New falconers may struggle with the precise monitoring and adjustment of their bird's weight, which is essential to ensure the bird remains healthy while being fit enough to hunt. If a bird is underweight, it may lack the energy required for effective hunting, whereas an overweight bird can become lethargic and unmotivated. This delicate balance is crucial and can be challenging for apprentices who might not yet have the experience to manage it properly.

In contrast, while the other options may pose challenges in falconry, they are less critical in evaluating a passage kestrel's overall suitability for training. For instance, difficulty in flying, inability to hunt, or aggression towards trainers, while important factors in other contexts, do not encapsulate the essential daily management responsibility that weight management entails, especially for a novice falconer.