 This study examined the temporal organization of circadian and ultradian rhythms in four different species. It was found that all four species exhibited similar patterns of rhythm with a branching appearance at 12 hours, 8 hours, and below in mammals and birds, and at 4 hours and below in yeast. These rhythms were characterized by scale-free fluctuations with long-range correlations below 4 hours. Additionally, synthetic time series models supported the idea that both circadian and ultradian rhythms are present within these species, with the circadian rhythm being at the center of the emerging pattern. This article was authored by J. M. Kembro, A. G. Flesher, P. S. Nieto, and others.