Final answer:
A blood feather can be identified by its dark, semi-transparent shaft and feather sheath. To differentiate between a blood feather and a mature feather, gently touching the feather can determine if it bleeds or causes any discomfort or pain for the bird.
Step-by-step explanation:
A blood feather is a new feather that is still growing and has a blood supply running through it. It appears as a dark, semi-transparent shaft with a feather sheath covering it. In contrast, a mature feather is fully grown and does not have a blood supply running through it. It appears as a solid, rigid structure with no sheath.
To further differentiate between a blood feather and a mature feather, you can gently touch the feather. If the feather bleeds or there is any discomfort or pain for the bird, it is a blood feather. This is why it is important not to trim a blood feather unless absolutely necessary, as it can cause bleeding and pain for the bird.