But where is the "is" part in this sentence ? Is the bird bad at "birding"? Or is the "다" used instead of "요", and the "이다" part is omitted? .
From what I gather from an answer in another sentence, 이다 can be contracted to 다 when it comes after a vowel.
EDIT: Found the other sentence discussion. I copy paste Avanade's answer here below.
Yes! :D It is official as long as you use it for proper occasions. I mean it is possible to use this shortened version when concerned noun words end with a vowel such as 바다(=sea), ex) 나는 가수이다 = 나는 가수다 (casual, shortened) 나는 변호사이다 = 나는 변호사다 (casual, shortened) 우리는 살인자이다= 우리는 살인자다 (casual, shortened) 살인자 = murderer In a conversational situation, many Koreans do not strictly distinguish between singular and plural. If you are sitting for a test, you may need to be a little more strict. 우리는 살인자들이다 살인자들 does not end with a vowel so you can not shorten. 우리는 살인자들다 (X) 가수 = singer 변호사 = lawyer However, 그것은 꿈이다(0) 그것은 꿈다 (x) since word 꿈 does not end with a vowel but a consonant (ㅁ) 꿈 = ㄲ + ㅜ + ㅁ 저것은 산이다(O) 저것은 산다(X) since word 산 does not end with a vowel but a consonant (ㄴ) 산 = ㅅ + ㅏ + ㄴ
It sounds unnatural and this course is still in ita beta phase, so you can report it if you want to
Can someone explain why writing: That bird over there is a bad bird, is considered incorrect?
Not all alternative sentences have been added yet, so in cases like this, you would need to report the sentence and request your answer be added.
So I can't translate this as "That bird is bad" when I could translate a similar sentence in this same lesson as "That movie is very bad"?
Not sure about the other sentence, but it'd have to be something like 저 새는 나빠요 to translate it like that. You can still try to flag it to see if they accept this alternate/more free translation.