kutibasi ga nagai.

It follows the very common pattern:

noun + が + い-adjective

So here:

• くちばし = beak
• が = marks what is being described
• 長い = long

So the sentence is structurally Beak + is long.

This is a complete sentence in Japanese, even though it may feel short in English.

が marks the thing that has the property long.

So くちばしが長い means something like:

• The beak is long
• It has a long beak (depending on context)

If you used は instead:

• くちばしは長い

that would sound more like As for the beak, it is long or The beak is long (as opposed to something else).

A simple way to think about it:

• が = focuses on the thing being described
• は = introduces the topic or contrast

In isolated example sentences, が is very natural.

No. 長い is an い-adjective.

In Japanese, い-adjectives can act like the main predicate of a sentence without needing a separate word for is in plain style.

So:

• くちばしが長い。 = The beak is long.

There is no hidden verb here. 長い itself is doing the job of is long.

Because this is in plain style.

Japanese often uses plain style in:

• dictionary entries
• captions
• casual writing
• simple example sentences
• statements in textbooks

You could make it polite by saying:

• くちばしが長いです。

That means the same thing, just more polite.

No. Japanese often leaves out information that is obvious from context.

So if you were looking at a bird, くちばしが長い。 could naturally mean:

• Its beak is long.
• This one has a long beak.

Japanese does this all the time. The listener is expected to understand the omitted subject from context.

Yes, but the structure changes.

If you want to say a long beak, you say:

• 長いくちばし

Here, 長い directly modifies the noun.

But in くちばしが長い, 長い is the predicate of the sentence:

• The beak is long

So compare:

• 長いくちばし = a long beak
• くちばしが長い = the beak is long / has a long beak

Yes, very often.

There are kanji forms, such as 嘴, but in everyday Japanese this word is commonly written in hiragana as くちばし.

This is normal for some animal- or body-related words, especially when:

• the kanji is uncommon
• the kanji is considered hard to read
• the text is aimed at a broad audience

So seeing くちばし in hiragana is completely natural.

長い is pronounced ながい.

Even though the kanji 長 can appear in other words with readings like ちょう, kanji often have multiple readings.

Here the word is the adjective 長い, whose normal reading is:

• ながい

This is just something you learn as part of the word.

Yes. In natural English, that is often the best translation depending on context.

Japanese literally says:

• The beak is long

But when describing an animal, English often prefers:

• It has a long beak

So both can match the Japanese idea. The exact English phrasing depends on what sounds natural in context.

Not by itself. くちばしの長い is usually a phrase that needs a noun after it.

For example:

• くちばしの長い鳥 = a bird with a long beak

Here, くちばしの長い modifies 鳥.

So compare:

• くちばしが長い。 = The beak is long. / It has a long beak.
• くちばしの長い鳥 = a bird with a long beak

This is a very useful pattern in Japanese.