Before the items that are complete sentences, write S. Before those that contain fragments, write F. Before a run on sentence, write RS.

1. We often walk through the woods, picking berries and listening to the birds.
Is this a run on sentence?

No. It's a correct complete sentence.

http://grammar.ccc.commnet.edu/grammar/runons.htm

To determine whether the given sentence is a run-on sentence, we should first understand the definition of a run-on sentence. A run-on sentence occurs when two or more independent clauses (complete thoughts) are combined without appropriate punctuation or conjunctions.

Let's break down the sentence provided: "We often walk through the woods, picking berries and listening to the birds."

This sentence consists of one subject, "we," and two independent clauses:
1. "We often walk through the woods."
2. "Picking berries and listening to the birds."

Since the independent clauses are separated by a comma without a coordinating conjunction (such as "and," "but," "or"), this sentence is categorized as a run-on sentence. Therefore, the label for this sentence would be RS (Run-on Sentence).