Peak expression of pro-inflammatory cytokines during the light phase or in alignment with the dark-to-light transition (eg. IL-1β in fat) in peripheral tissues, and a parallel reduction in anti-inflammatory cytokines (except in fat) is conceivable due to the increased demand of immunity during light hours when birds have a higher risk of exposure to infections when feeding, exploring, and interacting with other individuals21,52. This evidence concerns the gene IL1B and infection.