Los búhos anidan en el árbol.

In Spanish, the definite article is often used where English uses no article.

So Los búhos can mean:

• the owls if you mean a specific group, or
• owls in a general sense, as a class of animals

This is very common in Spanish:

• Los perros son inteligentes. = Dogs are intelligent.
• Los búhos anidan en el árbol. = Owls nest in the tree / The owls nest in the tree

Spanish usually sounds more natural here with los than with no article.

Búhos is the plural noun owls.

Its singular form is búho = owl.

So:

• el búho = the owl
• los búhos = the owls

It is a masculine noun, so it uses:

• el in the singular
• los in the plural

The accent mark in búhos helps show the correct pronunciation.

Búho and búhos are pronounced with two separate vowel sounds:

• bú-ho
• bú-hos

The h is silent, so the word is not pronounced like one smooth syllable such as buo. The accent on ú shows that the u is stressed and kept separate from the following o.

A rough pronunciation is:

• búho → BOO-oh
• búhos → BOO-ohs

Anidan is the third-person plural present tense of anidar.

The verb anidar means to nest or to make a nest / settle in a nest.

Conjugation in the present:

• yo anido = I nest
• tú anidas = you nest
• él/ella anida = he/she nests
• nosotros anidamos = we nest
• vosotros anidáis = you all nest
• ellos/ellas anidan = they nest

Here, anidan matches los búhos, which is plural.

Because Spanish often leaves out subject pronouns when they are not needed.

The verb ending already tells you who the subject is:

• anidan clearly shows they / the owls are doing the action

So Spanish normally says:

• Los búhos anidan en el árbol.

instead of:

• Ellos anidan en el árbol.

Adding ellos is possible, but usually unnecessary unless you want emphasis or contrast.

Spanish uses en in a broader way than English uses in or on.

En can mean:

• in
• on
• at

With birds or owls and trees, English often says in the tree, while Spanish says en el árbol.

So en el árbol is the normal Spanish expression here, even though English chooses the preposition differently depending on context.

Because Spanish only contracts a + el and de + el.

So:

• a + el = al
• de + el = del

But:

• en + el stays en el

So en el árbol is correct, not a contracted form.

Because the sentence is saying that the owls nest in the tree—one tree.

There is no rule saying a plural subject must have a plural location.

So:

• Los búhos anidan en el árbol. = The owls nest in the tree.
• Los búhos anidan en los árboles. = The owls nest in the trees.

The singular árbol simply means one tree, probably a specific one or the tree being talked about.

Árbol has an accent mark because the stress falls on the first syllable: ÁR-bol.

Without the accent, Spanish stress rules would suggest a different pronunciation. The written accent tells you the word is stressed irregularly.

So:

• árbol is pronounced roughly AR-bol

Its plural is:

• árboles = trees

It can do either, depending on context.

The Spanish present tense often covers both:

• a general truth or habit
• something happening now

So Los búhos anidan en el árbol could mean:

• Owls nest in the tree / Owls nest in trees as a general statement, or
• The owls are nesting in the tree if the context makes that clear

If you specifically want to emphasize right now, Spanish might also use:

• Los búhos están anidando en el árbol.

But the simple present is very common and natural.

Yes, but the meaning changes.

• en el árbol = in the tree / in the specific tree
• en un árbol = in a tree / in some tree

So:

• Los búhos anidan en el árbol. suggests a particular tree
• Los búhos anidan en un árbol. sounds less specific

Both are grammatically correct; they just express different levels of specificity.