Learn Spanish (Latin America): El pájaro tiene un año.

In Spanish, you don't "be" an age; you "have" years. To express age, you always use the verb tener (to have). So, El pájaro tiene un año literally translates to "The bird has one year."

Why is it un año and not uno año?

The number one is usually uno. However, when it comes directly before a masculine noun like año (year), it drops the final "o" and shortens to un.

What does the wavy line over the "n" in año do?

That wavy line is called a tilde, and it changes the letter into an ñ (pronounced like the "ny" in the English word "canyon"). In Spanish, ñ is a completely different letter from a regular n. Leaving it off changes the meaning of the word entirely, so it is very important to include it!

Why does pájaro have an accent mark on the first "a"?

The accent mark tells you exactly where to put the spoken stress or emphasis. By default, words ending in a vowel usually have the stress on the second-to-last syllable (which would sound like pa-JA-ro). The written accent breaks that rule, telling you to stress the first syllable instead: PA-ja-ro.