Spray application of fluorescent particles is a widely used and very valuable technique for marking birds. This remains one of the few practical means to mark large numbers of birds for monitoring movement, despite recent availability of a variety of more technologically advanced options. We monitored the longevity of the DayGlo fluorescent particle marker on red-winged blackbirds under simulated field conditions in a flight pen, and in an observational field experiment. In the pen study we banded 52 red-winged blackbirds with individually numbered leg bands, and sprayed them with DayGlo fluorescent particle marker from a distance of ~50 cm, on 1 December 2004. These birds were recaptured and DayGlo fluorescent particle marks assessed 11 times until 10 August 2005. All 31 surviving birds at the conclusion of the study (i.e. after 254 days) retained at least some DayGlo fluorescent particle marker on one or more body regions. Wings retained DayGlo fluorescent particle marks longer than other body regions and thus could be used to identify marks in large-scale collections. Roosting wild blackbirds aerially marked in September and October 2005 retained marks through June 2006, 263 days after marking. The formulation used is inexpensive (US$4.00 L^-1), easy-to-apply at many scales and practical for many species (e.g. starlings, blackbirds, sparrows, gulls and shorebirds).