You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Bird_migration

Context:
Many, if not most, birds migrate in flocks. For larger birds, flying in flocks reduces the energy cost. Geese in a V-formation may conserve 12–20% of the energy they would need to fly alone. Red knots Calidris canutus and dunlins Calidris alpina were found in radar studies to fly 5 km/h (3.1 mph) faster in flocks than when they were flying alone.

Question:
How much energy do geese conserve flying in a flock?

12–20%