"Magpies are noisy."
the former is a statement being noisy while the latter is the dictionary form
I don't think i will ever understand when to use 는 vs 가. Would it be fair to say there's no equivalent in English?
look at it like this, 이/가 are used for generic statements and 는/은 are used when comparing something or introducing a new topic. the lack of context duolingo gives is one reason a lot of people get these wrong I think. but there are more rules for when to put 이/가 that don't apply here yet.
It takes some getting used to.