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Human chronotypes (differences in preference for early or late rising each day) have been extensively studied in recent years, but no attempt has been made to compare human chronotypes with the chronotypes of other animal species. We evaluated behavioral chronotypes in 16 mammalian species along a body size gradient of five orders of magnitude (from mice to cattle). Individuals of all species were studied under a 12L:12D photoperiod in a thermoneutral environment with food and water available at all times. Rhythms of locomotor activity were analyzed for onset time, acrophase, and robustness. Neither of these rhythmic parameters was significantly related to body size, but onset time and acrophase varied considerably from species to species, thus characterizing diurnal and nocturnal species. Chronotype spreads ranged from less than an hour in sheep to almost 24 hours in cats, thus extending both below and above the human chronotype spread of 6 hours. The variability of chronotype (as quantified by the standard deviation of group means) was much larger between species than within species and also larger between individuals of a species than within individuals on consecutive days. These results help situate the matter of human chronotypes within the broader context of variability in the phase angle of entrainment of circadian rhythms in animals.


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This is an author-produced, peer-reviewed version of this article. © 2016, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-No Derivatives 4.0 License. Details regarding the use of this work can be found at: . The final, definitive version of this document can be found online at Physiology & Behavior, doi: 10.1016/j.physbeh.2016.04.019