Small desert birds are typically diurnal and highly mobile (hence conspicuous) whereas small non-volant mammals are generally nocturnal and less mobile (hence inconspicuous). Birds are more mobile than terrestrial mammals on a local and geographic scale, and most desert birds are not endemic but simply move to avoid the extremes of desert conditions. Many small desert mammals are relatively sedentary and regularly use physiological adjustments to cope with their desert environment (e.g., aestivation or hibernation). It seems likely that prey activity patterns and reduced conspicuousness to predators have reinforced nocturnality in small desert mammals. Differences such as nocturnality and mobility simply reflect differing life-history traits of birds and mammals rather than being a direct result of their differences in physiological capacity for tolerating daytime desert conditions.