Natural ultraviolet-b exposure of the Texas Horned Lizard (Phrynosoma cornutum) at a North Texas Wildlife Refuge

Abstract

Abstract We monitored daily patterns of natural ultraviolet-B (UVB) exposure (measured using the ultraviolet index [UVI]) of the Texas horned lizard (Phrynosoma cornutum) in North Central Texas. The animals were active on unpaved road surfaces on warm sunny days in May and June in the morning (0800–1200 h) and in late afternoon and early evening (1800–2100 h). The UVI was high during the morning and was positively correlated with hour of the day and body temperature. The UVI was lower during the late afternoon and early evening and was negatively correlated with hour of the day. Body temperatures of the animals were higher than air temperature during both periods of road activity. On warm sunny days between the two periods of high road activity, lizards remained active in shaded off-road areas and received variable amounts of UVB exposure. Two lizards that were followed most hours on warm sunny days had similar UVB exposure doses (irradiance × time) for the day but showed different patterns of UVI irradia...