I know it is not easy to understand but If you want to say 'Animal is a bird' you can say 'Zwierzę jest ptakiem' or 'zwierzę to ptak'. 'To' is equal to 'jest' but you do not have to change the word 'ptak'. ;)
This is different funny example: 'Jestem tobą' and 'Ja to ty'. These both short sentenses mean 'I am you'. ;)
That would be 'Którym zwierzęciem jest ten ptak?'. The current translation is correct.
"jak"? that's "how"...
Oh, you mean "jakie" (a form of "jaki")? Well, but that's "What animal", so the answer could be absolutely any bird, while here, it suggests that we have a closed set of animals (let's say... 7. or 32. still closed) and one of them is a bird.