The duckling started swimming out of instinct when she followed the rest of the flock into the lake for the first time.

Do any commas need to be added?

No.

thanks

You're welcome.

In the given sentence, there is no need to add any commas. The sentence is grammatically correct as it is.

To determine whether commas need to be added in a sentence, you can consider a few guidelines:

1. Use a comma to separate items or elements in a list:
Example: "I bought apples, oranges, and bananas."

2. Use a comma to separate two independent clauses (complete sentences) when joined by a coordinating conjunction (such as "and," "but," "or," "so," etc.):
Example: "She loves to read, and he enjoys watching movies."

3. Use a comma after introductory words, phrases, or clauses that come at the beginning of a sentence:
Example: "After finishing her work, she went for a walk."

4. Use a comma to set off nonessential information or clauses:
Example: "John, who is my neighbor, is a talented musician."

5. Use a comma to set off direct quotations:
Example: "She said, 'I will be there soon.'"

By applying these guidelines, you can determine if commas are needed in a particular sentence. However, it's important to note that the rules of comma usage can sometimes be subjective and depend on the specific style guide you are following.