El niu és petit, però l'ocell torna sempre a la mateixa branca.

Because Catalan usually shortens el or la before a word that begins with a vowel or silent h.

• el ocell → l'ocell
• la amiga → l'amiga
• el home → l'home

This is called elision, and it works much like l' in French. So l'ocell simply means the bird.

És is the 3rd person singular of ser: is.

The accent is important because és and es are different words:

• és = is
• es = a reflexive or unstressed pronoun, like himself/herself/itself in some contexts

So in El niu és petit, the accent tells you this is the verb is.

Because petit agrees with niu, and niu is masculine singular.

In Catalan, adjectives usually agree in gender and number with the noun they describe:

• el niu petit = the small nest
• la branca petita = the small branch
• els nius petits = the small nests
• les branques petites = the small branches

So petit is the correct form for niu.

Because mateix also has to agree with the noun it modifies.

The base idea is same, but the form changes:

• mateix = masculine singular
• mateixa = feminine singular
• mateixos = masculine plural
• mateixes = feminine plural

Since branca is feminine singular, you need la mateixa branca = the same branch.

Because tornar often takes a before the place someone or something returns to.

So:

• tornar a casa = to return home
• tornar al niu = to return to the nest
• tornar a la branca = to return to the branch

In this sentence, a la mateixa branca means to the same branch.

Because al is the contraction of a + el only.

• a + el = al
• a + la = a la (no contraction)

So:

• al niu = to the nest
• a la branca = to the branch

Since branca is feminine and uses la, the sentence has a la mateixa branca.

Torna is the 3rd person singular present tense of tornar.

Basic present-tense forms:

• jo torno = I return
• tu tornes = you return
• ell/ella torna = he/she/it returns
• nosaltres tornem = we return
• vosaltres torneu = you all return
• ells/elles tornen = they return

Here, the subject is l'ocell, which is singular, so torna is the correct form.

Yes, Catalan word order is somewhat flexible, and sempre can appear in different positions.

This sentence uses a very natural order:

• l'ocell torna sempre a la mateixa branca

But you could also hear:

• l'ocell sempre torna a la mateixa branca

Both are correct. The version with torna sempre is very neutral and common. In general, adverbs like sempre often go near the verb, but exact placement can shift depending on emphasis and style.

Però means but.

The accent is part of the standard spelling. It also shows the stressed vowel is ò.

So:

• El niu és petit, però l'ocell torna...
• The nest is small, but the bird returns...

The comma before però is also normal, just like before but in English when it links two clauses.

Because Catalan often does not need subject pronouns.

The verb ending usually tells you the person, so pronouns like jo, tu, ell, ella are often omitted unless they are needed for emphasis or contrast.

Here, the subject is already clearly stated as l'ocell, so adding ell would be unnecessary in normal speech.

You could even omit the noun in context:

• Torna sempre a la mateixa branca.
• It always returns to the same branch.

That works if everyone already knows you are talking about the bird.

In this sentence, it simply means the same branch.

But mateix / mateixa can sometimes add emphasis in other contexts, especially when it comes after a noun or pronoun. Here, though, la mateixa branca is the normal, straightforward way to say the same branch.

So the phrase is not especially dramatic here; it just identifies that the bird keeps returning to one specific branch.