Я люблю наблюдать за птицами в парке.

Because after люблю (I love / I like), Russian normally uses the infinitive to say what someone likes doing.

• люблю наблюдать = I love to watch / I love watching
• not люблю наблюдаю, because наблюдаю is a conjugated form meaning I watch / I am watching

So the structure is:

• Я люблю + infinitive
• I like/love + verb

Examples:

• Я люблю читать. = I love reading.
• Я люблю гулять. = I love walking.

Yes, люблю comes from любить and literally means I love. But in Russian, it is also very commonly used where English might say I like.

So Я люблю наблюдать за птицами в парке can feel like:

• I love watching birds in the park
• or simply I like watching birds in the park

The exact strength depends on context. Russian uses любить quite naturally for hobbies and activities.

Because наблюдать requires the preposition за when you mean to watch / observe something or someone.

So the pattern is:

• наблюдать за кем? за чем?
• to observe / watch whom? what?

Examples:

• наблюдать за детьми = to watch the children
• наблюдать за звёздами = to observe the stars
• наблюдать за птицами = to watch the birds

This is just something you need to learn together with the verb:
наблюдать за + instrumental case

Because after за with наблюдать, the noun goes into the instrumental case.

The basic form is:

• птицы = birds (nominative plural)

But after наблюдать за... it becomes:

• птицами = with/by birds in form, but here it means birds after the verb observe/watch

So:

• наблюдать за птицами = to watch birds

This is a very important pattern:

• за + instrumental

More examples:

• за другом = (after) friend in instrumental singular
• за друзьями = (after) friends in instrumental plural
• за собакой = watching the dog

Because here в парке answers the question where?, not where to?

• в парке = in the park → location
• в парк = into the park / to the park → direction

In this sentence, the person is watching birds in the park, so it is a location. That means Russian uses the prepositional case after в.

• парк → в парке

Compare:

• Я гуляю в парке. = I’m walking in the park.
• Я иду в парк. = I’m going to the park.

Because Russian has no articles like a, an, or the.

So:

• птицами can mean birds / the birds
• в парке can mean in a park / in the park

The exact meaning comes from context.

In this sentence, English naturally says in the park, but Russian simply says в парке.

Yes, very often.

Russian verbs usually show the subject clearly, so люблю already means I love. That means you can say:

• Я люблю наблюдать за птицами в парке.
• Люблю наблюдать за птицами в парке.

Both are correct.

Including Я can:

• make the subject explicit
• add a little emphasis
• sound slightly more complete in isolation

Omitting it often sounds natural in conversation.

Both can relate to watching, but they are not exactly the same.

• смотреть на = to look at
• наблюдать за = to observe / watch carefully, over a period of time

So наблюдать за птицами suggests something like birdwatching or observing birds with attention.

Compare:

• смотреть на птиц = look at the birds
• наблюдать за птицами = watch/observe the birds

In this sentence, наблюдать is especially natural because it suggests calmly observing birds in a park.

Because люблю usually describes a general preference or habitual activity, and Russian normally uses the imperfective infinitive for that.

• наблюдать = imperfective, ongoing/repeated activity
• It fits the idea of I like/love doing this in general

If you used a perfective verb, it would sound more like loving a completed single action, which is usually not what you mean with hobbies or habits.

So:

• Я люблю читать.
• Я люблю плавать.
• Я люблю наблюдать за птицами.

All of these use imperfective verbs because they describe activities in general.

The neutral word order is:

• Я люблю наблюдать за птицами в парке.

This is a standard, natural way to say it.

Russian word order is more flexible than English, so you can move parts around for emphasis. For example:

• В парке я люблю наблюдать за птицами.
  = In the park, I love watching birds.
  (emphasizes the place)

• За птицами я люблю наблюдать в парке.
  = possible, but more marked; it emphasizes birds

Even though Russian allows this, the original version is the most neutral and best for learners to use first.

A helpful stress pattern is:

• Я люблю́ наблюда́ть за пти́цами в па́рке.

Approximate pronunciation:

• ya lyub-LYU na-blyu-DAT' za PTI-tsa-mi v PARK-e

A few useful notes:

• люблю́ has stress on the last syllable
• наблюда́ть has stress on the last syllable
• пти́цами has stress on the first syllable
• па́рке has stress on the first syllable

Also, я is often pronounced quickly in normal speech.

In practice, it describes the whole situation: the watching happens in the park.

English also works this way:

• watching birds in the park

This usually means the activity takes place in the park, and probably the birds are there too. Russian does not need any extra marker here; в парке naturally attaches to the action.

So the sentence is understood as:

• I love watching birds while in the park
• or more naturally, I love watching birds in the park