A flock of feathered fliers

The term "a flock of birds" is a noun phrase, a group of Words based on a noun that functions as a noun in a sentence.

The noun "flock" is functioning as a collective noun for the group of birds.

The noun phrase "a flock of birds" also contains the prepositional phrase "of birds".

Example functions of the noun phrase:

• A flock of birds is roosting in the trees along the road. (subject of the sentence)
• The direction that a flock of birds takesin the fall is usually southbound. (subject of the relative clause)
• We watched a flock of birds as it disappeared over the horizon. (direct object of the verb 'watched')
• The lady sits in the park with a bag of crusts for aflock of birds. (object of the preposition 'for')