Birds can rely on a variety of cues for orientation during migration and homing. Celestial rotation provides the key information for the development of a functioning star and/or sun compass. This celestial compass seems to be the primary reference for calibrating the other orientation systems including the magnetic compass. https://www.chiggate.com/turbo-air-m3f72-3-n-78-wide-m3-series-reach-in-freezer-featuring-three-solid-doors-energy-star-online-now/