How to recognise *when* to use a passive construction?

Question

While I was reading articles about nature, I noticed that a lot of the descriptions are in the passive voice, i.e, they use werden instead of sein. If I were the author writing in English, I would have used to be, however this has not been the case in the following examples and it is confusing for me in regards to recognising exactly when I should then use the passive voice in German.

Der X ist keine bedrohte Tierart, aber er wird wegen seines Aussehens gefangen

Die Y sind zwar gesetzlich geschützt, aber in manchen Gegenden wird dieses Gesetz nicht streng gehandhabt.

In Z werden diese Katzen geschützt, in anderen Staaten sind sie eine beliebte Jagdbeute.

My confusion arises because in English for the first sentence, I would have said

The X is not a threatened species, however is caught because of its looks.

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1. How does one recognize when one should use the passive voice?

2. Would the above sentences sound strange to a German if sein was used instead? For example:

   In Z sind diese Katzen geschützt, in anderen Staaten sind sie eine beliebte Jagdbeute.

Answer 1

I'll start with an answer to number 2. Yes, the sentence would sound strange. There is a blurry line between a passive construction and a simple adjective assignment.

The house is large.

This is clearly not a passive.

The house is sold.

This is the same structure but it sounds passive because "sold" is derived from a verb. So the sentence implies that at some point the bike "was being sold".

German has two forms of passive. One is talking about the result. That's basically what the English passive does.

Das Haus ist verkauft.
The house is sold.

The other German passive, the werden-passive, focuses on the ongoing process. In English this would be done by using the progressive aspect.

Das Haus wird verkauft.
The house is being sold/The house is for sale.

This progressive form in English might is rather complicated so you'll often find different phrasings there instead. The German werden-passive is a little more handy.

Now, since German has two passives, the sein-passive is really only about the final result, while for ongoing processes you need the werden-passive. That is why "ist gefangen" would sound as if the hunt is over. But it's an ongoing hunt so we need the werden-passive. Technically, it would translate to

is being caught

in English, but the English sein-passive is more open to context than the German one.

EDIT:

In your last example you could use either version. Both sound idiomatic since "protection" makes sense both as a result and as a process.

Answer 2

As an addition to the already given answer:

In your example, the passive is favored because the focus should be the specified animal / subject. If using active, the author would have to specify the "Who" i.e. Who hunts the cat ?

Die Katzen werden wegen ihres Aussehens gefangen.

-> passive, focus only on the actual subject, i.e. Katzen;

Wilderer fangen Katzen wegen ihres Aussehens.

-> active, yet the subject is Wilderer, Katzen is only object here.

I think that makes clear, why passive is used throughout your texts. When reading texts, you instinctively focus on the subject, as its place inside the sentence is more prominent and we learned that the subject is usually the "important" thing inside the sentence. In your texts, it would draw attention from the actual animal towards the poachers / hunters, which is not what the author wants.