Ultraviolet (UV) plumage is thought to be sexually selected through intra-sexual competition, female choice and differential allocation. Experimental manipulations of plumage UV reflectance are essential to demonstrate that mate choice or intra-sexual competition are causally related to UV coloration. The most widely-used technique for manipulating UV reflectance in wild birds is the application of a mixture of UV-absorbing chemicals and preen gland fat. However, although this UV reduction technique is commonly used, little is known about the persistence of the treatment and the temporal variation in UV reflectance that it causes. We manipulated the UV crown plumage of wild and captive blue tits Parus caeruleus, and took repeated photospectrometric measurements of both UV-reduced and control-treated individuals. Our results show that the UV reduction lasts for at least five days and that the treatment has no negative effects on the survival of wild birds.