Thank you. I have dispatched enough animals/birds over my lifetime that I feel comfortable sharing my knowledge if it can help someone. Most people do not wish to dispatch an animal and I have always taken over because I don't want any creature to suffer, especially once it's clear all avenues have been exhausted. I was the grim reaper for my section of the hog barn and have been the grim reaper for decades on this farm. Now I live trap poultry predators. I take pride in being able to end life in one shot, as quickly and painlessly as humanly possible rather than leaving them to suffer. It is a depressing subject, but one necessary to discuss.
The pellet gun I use fires a .177 pellet and uses a spring piston.
The gun is rated at 450 FPS, which is more than adequate to dispatch a full-sized bird when shot at the back of the head at the base of the skull, which is my preference. The gun would be about 8-10 years old I believe.
The following is my guidelines.
Blunt force trauma: Most small animals/birds that's a baby, small lambs, piglets, rats
.177 pellet gun: full-sized poultry; chickens, small ducks, guineas, mice, rats, baby bunnies (if something's wrong)
(Blunt force trauma can work for most of these as well.)
22 rifle: for anything larger; dogs, cats, foxes, skunks, raccoons, sheep, calves
Full-sized cattle: .243 rifle