Golub kljuca mrvice kruha na pločniku.

Golub is the nominative singular form, which is the form used for the subject of the sentence.

Here, golub = pigeon, and it is the one doing the action of pecking, so nominative is the correct case.

• golub = a pigeon / the pigeon
• subject of the sentence = golub

Croatian does not use articles like a or the, so golub can mean either a pigeon or the pigeon, depending on context.

Kljuca means pecks.

Its dictionary form, or infinitive, is kljucati = to peck.

So:

• kljucati = to peck
• golub kljuca = the pigeon pecks / is pecking

In Croatian, the present tense often covers both English simple present and present continuous, depending on context. So golub kljuca can mean:

• the pigeon pecks
• the pigeon is pecking

Mrvice means crumbs.

It is the direct object of the verb, because those are the things the pigeon is pecking.

The singular noun is:

• mrvica = crumb

Its plural is:

• mrvice = crumbs

In this sentence, mrvice is in the accusative plural, which for this noun looks the same as the nominative plural.

So the learner may notice that mrvice could look like either:

• nominative plural: crumbs
• accusative plural: crumbs as the object

Here it is accusative because it receives the action of the verb.

Mrvice kruha literally means crumbs of bread.

Croatian often expresses this kind of idea with:

• a noun
• followed by another noun in the genitive

So:

• mrvice = crumbs
• kruha = of bread

The base form is:

• kruh = bread
• kruha = of bread / bread's / some bread, depending on context

So mrvice kruha is a very natural Croatian way to say bread crumbs.

Because after mrvice, Croatian uses the genitive to show what the crumbs are made of or come from.

So:

• kruh = bread
• kruha = of bread

This is similar to English bread crumbs, but Croatian builds it more like crumbs of bread.

This pattern is very common in Croatian:

• čaša vode = a glass of water
• boca vina = a bottle of wine
• komad kruha = a piece of bread
• mrvice kruha = bread crumbs / crumbs of bread

Because na here means on, and it is expressing a location: where the pigeon is pecking.

When na shows location, it usually takes the locative case.

So:

• pločnik = sidewalk / pavement
• na pločniku = on the sidewalk / on the pavement

This is an important pattern:

• na + locative = on/at a place, with no movement
• na + accusative = onto a place, with movement toward it

Compare:

• Golub je na pločniku. = The pigeon is on the sidewalk.
• Golub leti na pločnik. = The pigeon is flying onto the sidewalk.

Pločniku is in the locative singular.

The base form is:

• pločnik = sidewalk / pavement

After na meaning on in a static location, Croatian uses the locative:

• na pločniku = on the sidewalk

So this form answers the question Where?

Croatian normally does not use articles.

So a noun like golub can mean:

• a pigeon
• the pigeon

And na pločniku can mean:

• on a sidewalk
• on the sidewalk

The exact meaning depends on context. This is very normal in Croatian, and learners have to get used to understanding definiteness from the situation rather than from articles.

Yes. Croatian word order is fairly flexible, because cases show the grammatical role of each noun.

The neutral order here is:

• Golub kljuca mrvice kruha na pločniku.

But other orders are possible, for example:

• Na pločniku golub kljuca mrvice kruha.
  Emphasizes the location first: On the sidewalk, a pigeon is pecking bread crumbs.

• Mrvice kruha golub kljuca na pločniku.
  Emphasizes the crumbs.

Even though word order can move around, the most natural basic order is often subject + verb + object + place, which is what this sentence uses.

A few sounds may stand out to an English speaker:

• lj in kljuca is a single Croatian sound, similar to the lli in some pronunciations of million, though not exactly the same.
• č in pločniku sounds like ch in church.

A rough guide:

• golub ≈ GO-lub
• kljuca ≈ KLYOO-tsa
• mrvice ≈ MR-vee-tse
• kruha ≈ KROO-ha
• na pločniku ≈ na PLOCH-nee-koo

These are only approximations. Croatian pronunciation is generally quite regular, so once you learn the sound of each letter or letter combination, reading gets much easier.

Kljucati is imperfective.

That fits well here, because the sentence describes an ongoing or repeated action:

• the pigeon is pecking
• the pigeon pecks

Imperfective verbs are commonly used for:

• actions in progress
• habitual actions
• repeated actions

That is why kljuca sounds natural in this sentence.

Yes. That is a very good translation.

Croatian present tense often matches both:

• The pigeon pecks bread crumbs on the sidewalk
• The pigeon is pecking at bread crumbs on the sidewalk

In natural English, is pecking at bread crumbs may sound more idiomatic in this context, but the Croatian sentence itself is straightforward present tense.

Here is the breakdown:

• Golub — subject; nominative singular; pigeon
• kljuca — verb; 3rd person singular present; pecks / is pecking
• mrvice — direct object; accusative plural; crumbs
• kruha — genitive singular; of bread
• na pločniku — prepositional phrase showing location; on the sidewalk

So the structure is:

subject + verb + object + location

It depends on the variety of English.

• In American English, pločnik is usually sidewalk.
• In British English, it is usually pavement.

So both are correct:

• on the sidewalk
• on the pavement

The Croatian word pločnik refers to the pedestrian path along a street.