Фермер говорит, что ночью там можно услышать волка, хотя медведь приходит реже.

Because волка is the accusative singular form of волк.

In Russian, masculine animate nouns take an accusative form that looks like the genitive:

• nominative: волк = wolf
• accusative: волка = a/the wolf

Since услышать means to hear and the wolf is the direct object, Russian uses волка.

Compare:

• Я вижу стол. = I see a table.
• Я вижу волка. = I see a wolf.

The second one changes because волк is animate.

Because медведь is the subject of приходит, so it stays in the nominative case.

In this part:

медведь приходит реже

the bear is the one doing the action of coming, so nominative is required.

You would only get медведя if the bear were an object, for example:

• Я вижу медведя. = I see a bear.

But here it is:

• Медведь приходит. = A/The bear comes.

Ночью is a very common Russian way to say at night. It is the instrumental singular form of ночь.

Russian often uses the instrumental case for certain time expressions:

• утром = in the morning
• днём = during the day / in the daytime
• вечером = in the evening
• ночью = at night

So even though it may not look logical from an English point of view, this is just a standard idiomatic pattern.

This is an impersonal construction meaning something like:

• it is possible to hear
• one can hear
• you can hear

So:

там можно услышать волка
literally = there it is possible to hear a wolf

There is no personal subject like you or someone. Russian often uses можно + infinitive to express general possibility.

Examples:

• Здесь можно курить. = You can smoke here.
• Отсюда можно увидеть море. = You can see the sea from here.

They are being used for different ideas.

• услышать is perfective, focusing on a complete event: to hear / to catch the sound of
• приходит is imperfective, describing something that happens habitually or repeatedly: comes

In this sentence:

• можно услышать волка = it is possible to hear a wolf (a complete hearing event)
• медведь приходит реже = the bear comes less often (repeated behavior)

So the aspect choice fits the meaning very naturally.

Yes, but it would feel a bit different.

• услышать stresses the event of hearing something, often as a distinct occurrence
• слышать is more like to hear in a general or ongoing sense

So:

• можно услышать волка = you may hear a wolf / it is possible to hear a wolf
• можно слышать волка would sound less natural here in standard usage

With можно, Russian often prefers a perfective infinitive when talking about a possible single occurrence.

Что introduces a subordinate clause after говорит.

So:

Фермер говорит, что...
= The farmer says that...

This is very common in Russian:

• Он знает, что это правда. = He knows that it is true.
• Она сказала, что придёт. = She said that she would come.

English sometimes drops that, but Russian usually keeps что in this kind of sentence.

Хотя means although, though, or even though.

It introduces a contrast:

• you can hear a wolf there at night
• although the bear comes less often

So the second part gives additional information that partly contrasts with what came before.

Examples:

• Хотя было поздно, мы не ушли. = Although it was late, we didn’t leave.
• Хотя он устал, он работал дальше. = Although he was tired, he kept working.

Реже means less often or more rarely.

It is the comparative form of редко = rarely.

So:

• редко = rarely
• реже = less often / more rarely

In natural English, less often is usually the best translation here.

Example:

• Летом он приходит редко. = In summer he comes rarely.
• Зимой он приходит реже. = In winter he comes less often.

That is a normal and natural word order, but Russian word order is flexible.

Here:

ночью там можно услышать волка

the speaker first sets the scene:

1. ночью = at night
2. там = there
3. можно услышать волка = one can hear a wolf

Russian often places time and location information early in the clause.

Other orders are possible, but they may shift emphasis:

• Там ночью можно услышать волка.
• Волка там можно услышать ночью.

These all express roughly the same basic meaning, but the focus changes slightly.

It can mean either, depending on context.

Russian has no articles, so волка does not itself tell you whether it is:

• a wolf
• the wolf

You understand that from the situation and the wider context.

In this sentence, English would most naturally say a wolf, because it sounds like a general statement about what can be heard there at night.

Grammatically, приходит is present tense, but with an imperfective verb it often expresses a habitual action.

So here it does not mean the bear is coming right now. It means something more like:

• the bear comes
• the bear tends to come
• the bear shows up

And because of реже, the meaning is clearly habitual:

медведь приходит реже
= the bear comes less often

Because Russian often leaves that idea unspoken in impersonal constructions.

English might say:

• you can hear a wolf there at night
• one can hear a wolf there at night

Russian simply says:

• там можно услышать волка

The idea of a general person is built into можно + infinitive. This is very common and very natural in Russian.

Not exactly, because the Russian says медведь in the singular, not медведи in the plural.

So the Russian more literally means:

• although the bear comes less often
• or possibly although a bear comes less often

Russian singular nouns are often used in a general sense, especially when talking about animals as a kind or typical visitor. English sometimes prefers a plural in such cases, but the Russian sentence itself is singular.