Do they preen each other? Hang out together? Mate?
What sex was the injured bird? And the sex of the other?
I´m wondering a few things...
Are they really bonded? And are they actually fighting?
If the birds are bonded, it´s unlikely they are fighting, but not impossible. That happens when hormones are involved usually.
Have you checked the cage to be sure they didn´t injure themself on something in there?
Spend as much time near the cage to observe and figure out what is going on.
If you see an attack (not to be confused with bickering), then separate the birds.
Jeff - dna tested (female)
Nate - not dna tested (sex unknown)
Jeff is super sweet and innocent. Nate can get moody and territorial sometimes. While they are in the cage they can get into little fights. Nate will lunge at Jeff and chase her around the cage. It doesn't usually last more than a minute or two. They usually fight when Jeff is trying to eat, even though they have multiple bowls and shouldn't have to eat at the same one. sometimes they fight for no reason. However when they are taking naps or getting sleepy, they will cuddle on the same perch and preen each other.
Outside of the cage they don't fight at all. They follow each other around, eat from the same bowl, and get along well. They clearly love each other very much
A few weeks ago was when their behavior changed a bit. They were trying to mate pretty regularly for a few days. Then a week later Jeff gained a few grams, so I assumed she was going to lay eggs. I put some extra calcium in their food, I was better about weighing her every morning. I put a box in the cage to give her a spot to make a nest if she was going to lay eggs. Nate started to get territorial over the box. A week later a decided to take the box out because I came to the conclusion that she wasn't really going to lay eggs. A few days ago I notice that Jeff has blood on her leg when I uncover the cage. Since then, I haven't noticed fresh blood. I had been checking on her whenever I got the chance to see if it got worse, which it hadn't. This morning I wake up to some blood on her neck. All I could see was a tiny bit on the feathers on her neck. I haven't inspected it because they aren't comfortable with me petting or holding them. I have since put her in a travel cage while Nate is still in their normal cage. Even through all of this, they are perfect angels outside of the cage.
I have no proof that the injury was from a fight, other than the fact that Nate can be territorial at times.
I attached a picture of her leg. I took this pic yesterday.