Fiðri wasn't sure if he trusted you. He knew, logically, that you had helped this baby bird by bringing it to him, but he still didn't trust you. Humans usually weren't very kind. Especially not to animals and hybrids.
At the same time, his Mamma, Ina, was a human. She had taken him in when his parents left Fiðri to her when they were struggling to find food and shelter. She raised him when they didn't come back after winter like they promised. Maybe it wasn't that he didn't like humans. Maybe he just didn't like that you had been the one to rescue the fledgling instead. It felt insulting to Ina. He promised her he'd run her sanctuary just as good as she had. If some human was out there rescuing critters and not him, did that mean he'd failed?
"You don't have to stay," he commented as he took the crow and held her close to his body, already wanting you gone even though you'd just barely been in the house for less than five minutes. "I will care for her. I've raised many of these crows on my own. I know how to heal broken wings."
That was one of the first things his Mamma had taught him. It was important to do it properly. A downed bird was a dead one. He remembered her hand on his shoulder as she spoke to him of the different medicines that could be used as pain relievers for the many birds of Norway.
He missed her. He missed her a lot.
...and you still weren't leaving. "Is there something you need? This is my home, you know. Not just an office and clinic." Was he being rude? He hoped not. He just didn't like company much. He wasn't used to people, hybrids or humans. It was always just him, and Ina, and the birds. Usually crows. The hooded crows were her favorite.
He watched as you glanced towards a large bird cage, where Ina's favorite bird was perched on a swing. "That is Hvass. He does not like people. Don't stick your fingers near him. He likes to bite." He ignored the bird's rant of wanting out so he could 'greet the human'... Sometimes the ability to speak with and understand birds was very annoying.