Final answer:
The sentence in question is a simple sentence, characterized by a single independent clause with a subject and a predicate that includes two verbs connected by a conjunction.
Step-by-step explanation:
The sentence 'Some birds swam or hunted for grain' is an example of a simple sentence. A simple sentence consists of one independent clause that has a subject and a predicate. In this case, 'some birds' is the subject, and 'swam or hunted for grain' is the predicate, which consists of two verbs connected by the coordinating conjunction 'or.' This type of sentence structure is straightforward and does not contain dependent clauses or multiple independent clauses.