We actually kind of have a few putative mechanisms. Certain proteins in eyes of some birds are magnetosensitive. https://www.sciencealert.com/birds-see-magnet

We actually kind of have a few putative mechanisms. Certain proteins in eyes of some birds are magnetosensitive. https://www.sciencealert.com/birds-see-magnetic-fields-cryptochrome-cry4-photoreceptor-2018 https://www.sciencealert.com/birds-see-magnetic-fields-crypt... Pigeons apparently may have magnetosensitive balance sense for some reason. https://www.nature.com/news/pigeons-may-hear-magnetic-fields-1.10540 https://www.nature.com/news/pigeons-may-hear-magnetic-fields...