Nitrogen and Oxygen are two of essential elements for life. Though Carbons role can’t not be ignored, it is simply a building block upon which these other elements become a part of in straightforward and complex life. Axolotl is very similar to Salamanders which we probably remember from Beryllium. Axelottles choice here as the animal that represents Nitrogen is of particular importance though. Nitrogen in a biological system is essential for a cycle of growth, though occasionally things need rapid change and Nitrogen can do this. Much like Axolotl who can reproduce without undergoing metamorphosis. Nitrogen is also an excellent indicator of the health of a system. Axolotl is also used as an indicator species. Being amphibious they take up toxins, get sick and are easily bred for scientific research into aquatic systems, hearts, neural tube defects and many other embryonic development problems. They much like nitrogen also can comply regenerate without scaring. The Nitrogen cycles are very similar in that the same nitrogen that goes into a system also comes out of it. The last connection is an awful bioscience pun. Which I will save you from unless you wish to guess in the comments.
Ravens are incredibly intelligent birds. I try my best to match the elements that are gases at room temperature with birds, but as you can tell for nitrogen Axolotl made a far better match than any bird I could think of, though the connections get a little less complicated and semi scientific over time. Some only have the connection by their country of discovery or are simply animals that felt right at the time! Raven does like to form groups of two (two ravens are relatively common) though often these are solitary birds who have barely any real connection to the element Oxygen. It just felt right somehow. Maybe you have a theory or a connection I missed? Let me know in the comments.