Sometimes writers omit a word in a compound structure. They succeed with such an elliptical construction when the word omitted later in the compound is exactly the same as the word earlier in the compound.

That bell belonged to the figure of Miss Duling as though it grew directly out of her right arm, as wings grew out of an angel or a tail [grew] out of the devil.

—EUDORA WELTY, One Writer’s Beginnings

The omitted word, grew, is exactly the same verb that follows it and wings in the earlier parts of the compound. You should not omit a word that does not exactly match the word used in the other part(s) of the compound.

The verb is does not match the verb in the other part of the compound (are), so the writer needs to include it.