For me it is more a matter of scale and circumstance than principle.
I kill mosquitoes and flies, but safe bees and spiders. Why? I don't know.
I eat meat, and somebody said that that means that in total 1 or 2 cows will die just for me. And I hope to one day have the chance to kill and butcher one of them myself. Not for the fun of it, but because of the awareness of the consequences of my choice.
One of the reasons I entered druidry was because of the unnecesary slaughter of lifestock during the plagues. Foot and mouth, pig plague, bird flu.
Piles of burning corpses, foul smelling trucks on the highway on their way to crematoria, the forests off limits, farmers fighting off the police who came to bring the killers. I was disgusted to be a human, not because we kill animals, but because for the economic reasons behind this slaughter.
Another reason was that I had to kill a possum in New Zealand.
Humans introduced the animal in NZ, but it got out of hand, they multiplied and started to eat kiwi eggs. So, they introduced predators to eat the possums, but instead they started to eat the kiwi's. Now they are trying to eradicate all of that again, trying to kill milions and millons of animals by spraying poison over the rainforests and planting traps. They even have a slogan at the national parks, "be a good kiwi, kill a possum". I was disgusted by what they are doing there.
Then I ran into a trapped possum (an animal the size of a small dog), legs broken, full of sh*t and flies, eyes the size of saucers with shock. I felt trapped myself, because I felt the moral obligation to kill it to end its suffering, but I didn't agree with possums being slaughtered.
I took a big rock and was ready to slam its head in. But the possum did something very strange then. It spread all fours wide, fully exposing his body, looking me straight in the eyes, starting to squeek. It realised exactly what I was about to do and seemed to be surrendering in some way, it was certainly trying to tell me something. I've never heard of animals doing that.
This really shocked me and I backed off, and the possum rolled up in a ball again. But I still felt that I had to do it, so I lifted the rock again, and again the same scene, spreading all fours, looking me straigt in the eyes. But this time I hit, as hard as I could. Blood, brains and a very strong musk scent of mortal terror (I think). But damnit, it wasn't dead yet, so I kept hitting until it stopped moving. I was crying from frustration, anger and shame at that point. I was so ashamed to be human that I didn't want to see any humans and retreated into the woods for a few days. I couldn't get the musk smell of me, even when I scrubbed with water and soap. It stayed on me as a reminder of this shame, and I was glad of it. In that way I somehow honoured that animal.
A few days later I came to a small hiking cabin. There was a large deer hanging from a wooden frame, upside down, throat cut, tongue out of its mouth. When I entered the cabin there was a guy cleaning a rifle. And then something strange happened. He started apologizing to me. And he explained how he had been there for a week already, leaving the cabin before day break to stalk the herd of deer every morning. He spend a week just observing them, filming them (he showed me the film), to decide which animal to shoot. And the last day, he would shoot 1 animal, butcher it at the cabin, and load his backback full of meat to eat from it for the entire year. This man was going out of his way to prove to me that he had acted with honour. And he succeeded, and with that he washed away some of the shame of what had happened with the possum. I wasn't shocked by his story at all, nor by the sight of the dead deer, who was treated with this honour. And I gladly accepted a piece of that superb fresh deer steak that he cut from the animal there and then. And it was the best meat I ever tasted.
Long story, but I told it in this detailed blood and gore intensity to show two sides of the same medal. These experiences are closely linked, both strenghten each other in their contrast. Mystically speaking they are the two pillars of a gateway. One of the gateways that brought me to druidry. And it shows how for me it really depends on the circumstances, intentions and context how I feel (strongly) about killing animals. Or humans for that matter.
In the 'damaged bird' case. I would kill it without feeling very dramatic about it. Some sadness perhaps, and I would indeed try to honour it in some small way, but not really a big deal.
Extraordinary claims require extraordinary evidence