Which animals need hemoglobin that is good at binding to oxygen?

Animals that live in environments with low oxygen levels need hemoglobin that is good at binding to oxygen. This includes animals that live at high altitudes, such as yaks and mountain goats, as well as animals that live in water, such as fish and whales. Hemoglobin is a protein that carries oxygen in the blood, and it is essential for these animals to be able to survive in their environments.