Translation:My favorite animals are birds.
[Edit: The English has been corrected since this comment was first posted.]
The problem is that we can tolerate "birds are my favorite animal", even if it's incongruous. But it doesn't work with "are" if we put the singular noun first. The verb has to accord with the subject, not the with the complement.
"My favorite animals are birds" is definitely correct. And people will probably disagree as to its correctness, but "my favorite animal is birds" is also a way that native speakers sometimes put this kind of statement, and I dare say it's idiomatic (natural and accepted). It's just the reverse of "birds are my favorite animal", but since now there's a singular subject, we get a singular verb.
But as for your first sentence, I think "my favorite animal is the bird" is more correct as a general statement, as "a bird" suggests a particular bird, i.e. "一只鸟" (or perhaps "一种鸟", i.e. a particular kind of bird).
Those are both correct English but they reverse the order of the subject and complement relative to the Chinese.
The reversal is also possible in Chinese, and Duo tends to require the translation to follow the order of the original in such cases, so you can try reporting your suggestions as acceptable alternatives, but you might not achieve any satisfaction.
I disgaree with 'the bird'. 'The bird' suggests a particular bird, hence a definite article, while 'a bird' suggests a bird in general, hence the indefinite article. Though I see the logic behind your argument, I don't see a reason for using a definite article. If we talk about birds as a species in general, I would definitely use an indefinite article.
It depends. If you're talking about a particular species of bird, "a bird" works, as an elliptical rendering of "a kind of bird" (but then it's "一种鸟"). But if you're talking about all birds in general, I don't think "a bird" works in this construction. The king of the jungle is the lion, not a lion. (We're not talking about an individual lion. We're talking about the lion as an archetype.)
And see the butterfly example in the definite-article section of Wikipedia's article article:
The cabbage white butterfly lays its eggs on members of the Brassica genus.
And here's a British Council article that explains that "the wolf" is equivalent to "wolves in general":
You could say "... is a bird called the magpie", which corresponds to my assertion about "a kind of bird" – and then the definite article comes back in, in the naming of the kind.
For those interested in the nuances of the Chinese, "a bird" would be "一只鸟" or "一种鸟", depending on whether you meant a specific individual bird ("一只鸟") or a kind of bird ("一种鸟").
The Chinese sentence presented in this exercise, on the other hand, most likely refers to birds in general, which can be expressed by "birds" or "the bird" in English. It's not about nitpicking; it's about accuracy for the sake of proper learning.
In other words, it's about the most likely meaning of the Chinese, and how to translate it correctly to capture the right nuance, so we learn that meaning properly, and aren't misled by an inaccurate English rendering.
That is, it's precisely for the purpose of accurately learning the Chinese that we should care about the details of the English.
I'd say it's a stretch, and I personally wouldn't give full marks to a student who provided that translation on a test. In my opinion it would be misleading for Duolingo to allow it, because people wouldn't have cause to think about the correct nuance of the Chinese.
Marc, do you need my permission not to learn this nuance? You have my permission.
For anyone who feels differently and wants to learn it, I've put significant effort into explaining and finding resources. I appreciate it when others do the same for me.
I don't know what "a sinology level" means, but good luck learning Chinese and English to exactly the right level for you.
Please consider the average and desired level of DuoLingo students. Anybody who wants to study Chinese at a sinology level should and probably will go to university. With all due respect to anybody who wants to learn another language, I don't think this is the DuoLingo target audience... Also, you probably are a native English speaker? I myself speak five languages and I am not at all interested in British Council articles, yet I have never been told by any of my British or US colleagues that my English was not good enough, to the contrary. I could also ask my Chinese colleagues how they feel about the 'the bird or 'a bird'. They will very likely not care, they will know what I am saying.
That's right. Either that, or "I like birds, for most part, but not kingfishers." Anything of that sort, really.
I think you wrote about 我主要喜欢鸟 in another comment, that would be in the sense of "I mainly like birds, (but my interest extends to cats, as well as the occasional dolphin)."
Excellent, thanks again. Here's a link to that comment:
That seems unlikely. It usually accepts that sort of British (Canadian, Australian, etc.) spelling difference, and even if it didn't in this case, one extra letter would typically be marked as a typo.
You can always try reporting your answer, but it's likely that there was something else in it that Duo objected to.
For "I mostly like birds", I would imagine it depends on the precise nuance you're trying to convey. One option is "我比较喜欢鸟", and I think "我主要喜欢鸟" is also possible, but I defer to native Chinese speakers.
Here's a link to anther chain you started, which has more on this point from user KX3.:
Essentially the Chinese is saying "my most-liked animal" ("I-most-like 的 animal", i.e. "the animal that I most like"), which is equivalent to "my favorite animal".
Maybe it's elliptical without a "的" after "我", but often you can just save it for the end of the phrase.