I know that too well. And I find it very serendipitous that you have read Gerald Durrell, I grew up on his books!So very sorry.
I'm trying to comfort an strengthen myself with the knowledge that animals are not immortal as Gerald Durrell wrote in the first book about his Jersey zoo, but it isn't cutting it for me. You can't keep rabbits from being rabbits, I can't stop cattle from getting old or chickens from being subject to chickenish ills, but doesn't it always feel as if we should be able, if we just never made any mistakes nor had any bad luck, keep everything alive forever?
Went out to check animals, and the dog went after some predator. Turned out to be a loose rabbit - checked rabbitry and can not figure out how it got loose. No, open doors, holes or broken cages. Bizarre. And I can't run after it with the neck brace on. Got to wait til himself gets home and let him catchum!