La gallina sale del gallinero al amanecer.

Because sale is the conjugated verb, while salir is the infinitive.

In this sentence, the subject is la gallina, which is third-person singular, so salir becomes sale in the present tense.

Present tense of salir:

• yo salgo
• tú sales
• él/ella sale
• nosotros/nosotras salimos
• vosotros/vosotras salís
• ellos/ellas salen

So La gallina sale... = The hen comes out / leaves...

Spanish often leaves out subject pronouns because the verb ending already shows who is doing the action.

So instead of saying Ella sale del gallinero, Spanish usually just says La gallina sale del gallinero.

You would only add ella if you wanted extra emphasis or contrast, for example:

• Ella sale, pero el gallo no.
  = She comes out, but the rooster doesn’t.

Because de + el contracts to del in Spanish.

So:

• de + el gallinero → del gallinero

This is mandatory in normal Spanish. You do not usually say de el gallinero.

Spanish has only two common mandatory contractions:

• a + el = al
• de + el = del

For the same reason as del: a + el becomes al.

So:

• a + el amanecer → al amanecer

This expression means at dawn or at daybreak.

Here, amanecer is functioning as a noun.

As a verb, amanecer means to dawn or to get light.
But in the expression al amanecer, it means dawn/daybreak.

So:

• amanecer as a verb: Amanece temprano.
• amanecer as a noun-like expression: al amanecer = at dawn

This is very common in Spanish with words like:

• al amanecer = at dawn
• al anochecer = at nightfall
• al atardecer = at dusk

Because salir normally uses de to show the place something comes out of or leaves from.

So:

• salir de un lugar = to leave / come out of a place

Examples:

• Sale de casa. = She leaves the house.
• Sale del coche. = He gets out of the car.
• La gallina sale del gallinero. = The hen comes out of the coop.

Without de, the sentence would be incomplete here.

It can mean any of those, depending on context.

With del gallinero, the most natural idea is comes out of the henhouse / coop.

So salir is a flexible verb:

• leave
• go out
• come out

English chooses differently depending on perspective, but Spanish uses the same basic verb.

Spanish uses articles more often than English does.

Here, la gallina can mean:

• a specific hen already known in the context, or
• a general, natural subject in a descriptive sentence

Leaving out the article would usually sound incomplete in a normal sentence like this.

So Spanish prefers:

• La gallina sale...

rather than:

• Gallina sale... ✘

Because gallinero is a masculine noun, so it takes el:

• el gallinero

Even though it is related to gallina, the noun itself has its own gender.

Also, nouns ending in -ero are very often masculine:

• el granero
• el sombrero
• el gallinero

So:

• la gallina = the hen
• el gallinero = the henhouse / coop

It is built from gallina + the suffix -ero.

The suffix -ero often refers to a place associated with something. So gallinero is literally a place for hens.

That is why it means:

• henhouse
• chicken coop

It can be either, depending on context.

The Spanish present tense often covers both meanings:

1. Habitual

   • La gallina sale del gallinero al amanecer.
   • The hen comes out of the coop at dawn.
     = something it regularly does

2. Narrative / vivid present

   • It can also describe an event as if you are watching it happen.

If there is no extra context, many learners would understand it first as a habitual action.

Yes, but the original order is the most neutral and natural.

Neutral order:

• La gallina sale del gallinero al amanecer.

If you want to emphasize the time, you could say:

• Al amanecer, la gallina sale del gallinero.

Both are correct. The difference is mainly emphasis, not basic meaning.

These words are related but not the same:

• gallina = hen
• gallo = rooster
• pollo = chicken

Depending on context, pollo can mean:

• a young chicken
• chicken as food
• sometimes just chicken in a general sense

So in this sentence, gallina is used because it specifically means a female chicken, a hen.