It comes back to is my life more important than someone else life / the life of another specie.
It is a question for wich there is still debate.
It is today widely reconised that a man should give his life to save a woman or a child, the application being of course another problem lol,
but the sole idea of applying ethics to animals is kinda new, well not really new but at least new on this scale.
If you wanna read on the subject, there should be books in your bookshop, at least they are in the big ones and in the specialised ones like those on ethics, the university ones, and the alternatives ones like anarchists. You can also order.
It is also a problem of intrinsic value.
You can read Peter Singer and Gary Francione among others, from there there should be references to find easelly more books.
Personally i say no top the first because i don t think that my life has nore value than that of a chicken, and since i ve been in such situation and survived in extremis, i can safely say that i know what i m saying. I wouldn t kill a human in this situation neither btw. The Ethics being what they are, i would say that i comes down to a personal choice and personal beliefs, with some will to it and consciousness to it.
To the second question again i say no, just because in the abscence of need it is clearly against ethics to kill intentionally without need or without accident.