Chulin 3:3-4

Chulin 3:3

The following injuries render birds treifa: if the esophagus is pierced; the trachea is severed; if a weasel injures its head in a place that would render it treifa; the craw is pierced; the small intestine is pierced. If it fell into fire and burned its internal organs so that they turned green, the bird is a treifa but if they are red, it remains kosher. If a person stepped on it or knocked it into a wall, or if an animal crushed it but it’s still twitching, then if it survives for 24 hours before being slaughtered, it is kosher.

Chulin 3:4

The following birds are kosher: If the trachea is pierced or slit; if a weasel wounded its head in a place that doesn’t render it treifa; the crop is pierced – Rebbi says it is kosher even if the crop is completely gone; if its insides are sticking out but they’re not pierced; if its wings or legs are broken; if its wing feathers have been plucked. Rabbi Yehuda says that if its down (the layer of fine feathers under the exterior feathers) is gone, the bird is a treifa (analogous to an animal whose hide has been removed, in 3:2).